Dell Compellent’s Storage Array

Speeds and Scalability

Interview with Alan Atkinson VP & GM of Dell Storage

Optimal Membrane Switch Design

Reducing BOM in LED Designs

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eeweb.com/registerSince the early 1900s, PID compensators have

been one of the most widely used closed loop controllers in industrial applications. However,

the tuning of such controllers is widely considered a difficult art. Talking with anyone who is familiar with tuning often quickly leads to a very distressing discussion about poles, zeros, and margins which makes the casually inclined engineer either stop or, if they are feeling brave (i.e., deadlines closing in), tune the loop intuitively.

{Part 1}

PIDCONTROLLERS

MIXING SIGNALS:An Introduction to

by Michael Lyons, NXP Semiconductor

In designs that use LEDs, shifter registers can be very useful. For instance, if the system includes a seven-segment display, a single indicator, or an array of LEDs that form a grid or

panel, a standard 8-bit shift register can be used to allow a low pin-count microcontroller to drive multiple LEDs.

Using

in LED Designsto Reduce Size and BOM

SHIFT REGISTERS

Those are some of the trends in the traditional data center, but I think the more dynamic part of data centers—which is still relatively small but growing very rapidly—is what software defined for a data center. For example, private clouds that could be implemented as a private cloud or just more of a traditional type of on-demand service. That side of the world is very interesting. They tend to like very uniform footprints; they typically deploy things as pods so they become these sorts of building blocks and have dynamic workload changes applied with them. That’s an area we’re pretty excited about because we have a strong presence in server, storage, and networking—all three as well as services and software. We think that gives us a pretty unique advantage.

We try to put together solutions because in that part of the storage world, you don’t have to buy the traditional big storage array, top of the rack switch, a core switch, and so on. It’s a different type of architecture and we think we’re very well positioned there. It’s also an emerging technology, so if you were to compare dollars, you’re going to have a relatively small expenditure in that area. We spend a lot of time thinking about that space and we’re pretty excited about it.

As far as talking to the data centers and getting a feel for the things they’re looking for, how do environmentally friendly solutions come into play with data centers?

Well it’s not just storage; it’s our whole power and cooling footprint. In those cases, I think the trends that we’ve seen lately have been around what flash does for the storage environment. In regards to convergence—if you look at our VRTX product, for example—it has been a real game changer in the economics with power and cooling as well. But on the flash side, where we’ve really seen it, it’s not unusual that we can take 6U—ten times more worth of spindles—and collapse them down into 2U of flash. This is because people aren’t actually using all the data on those spindles and all they really care about is the performance characteristics. As soon as you go to solid state you change that discussion. Again, this is one of those cases where because we got to the current price point, we can now take a lot more spindles out than other vendors can. You can get pretty good rack compression and that obviously comes with a pretty good power and cooling state as well. It’s a lot cheaper not to have to run those motors. We’ve seen that be a pretty interesting benefit of the whole solid-state discussion.

What types of customers are using Compellent solutions?

We are still early on in the game, but I’m seeing deals go down with financials. Financials are very keen on this, which makes sense. They’re probably among the most data center constrained and some of the most performance hungry out there for their applications, so that’s not really surprising. We’re also seeing a lot of interested service providers.

Surprisingly, if we were to cross the other side, we’re getting a lot of general-purpose interest—the kind of customer that is putting out 3 terabytes of storage. If you look at how our customers buy, they buy a combination of performance and capacity. Just the fact that we’re basically at the price point that we were in May for capacity disks you can now buy, as far as performance disks, you can get 15k if you need. They can now buy flash—it’s just a real differentiator in that general-purpose market. It’s the same people that may have kicked the tires before but now they’re going to buy flash instead of disks.

Offering a product is only a portion of the solution here—the rest of it is providing support to your customers around these releases. What types of services does Dell offer to support its data storage products?

We have full professional services, which are one of the service leaders dating back from the Perot acquisition forward. As far as regular support, I think our copilot, which is the compellent support for our organization, is generally recognized as the best in the class support product. We don’t metric our folks on how many cases they close a day or by quantity. They really will stay on the phone with the customer as long as it takes—they’re

“If you look at how our customers buy, they buy a combination of

performance and capacity.”

Dell Compellent SC8000

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Featured ProductsThis week’s latest products from EEWeb.

1626

An Intro to PID ControllersThe first part of the series aims to demystify

the mathematical tunings involved in using PID controllers.

3426

1034

Mounted LED ConcernsSheer stress, vibration, or shock can take a toll on another part of the screen printed membrane keypad. Many membrane keypads incorporate surface mounted LEDs within the membrane sandwich. Printed silver circuits and polyester cannot tolerate soldering temperatures. LEDs are attached to the printed silver circuits with a small amount of silver-filled conductive epoxy.

In a perfect world, attaching and connecting LEDs to printed silver circuits with conductive epoxy sounds like a good idea. However, one of the inherent problems with polyester film used in flexible membrane switches is that the peel strength adhesion of hard coat texture inks, graphic ink, or silver-filled ink for circuit conductors is less than desired.

LED failures can occur when stress fractures transpire between the silver ink and the polyester at the LED location or along the silver ink conductor next to the LED. The failure starts to occur as a stress crack which may not cause an open circuit right away. When additional stresses are applied during temperature excursion, shock, vibration, intermittent, open circuits can develop causing the LED to be inoperative. Unfortunately there is no practical repair option.

These LED failures can occur even when the flexible membrane is mounted to a metal support plate. Imagine the reliability problems that can be initiated when LEDs are mounted in unsupported

Figure 2: Standard membrane switch stack-up.

flexible membrane keypads. Unsupported keypads are easily stressed during handling when removed from the shipping box, inspected, inventoried, and kitted for an Original Equipment Manufacturer (OEM) assembly line. Applied stresses may not cause any immediate problems. Most stress related LED problems do not show up until the product is in the customer’s hands. The later the failure is detected, the higher the total cost is to repair or replace.

Flexible membrane keypads include a flex tail that is part of the same polyester sheet that contains the circuit conductors in the polyester/adhesive keypad sandwich. Creasing, tearing, abrasion or vibration can easily damage the flex tail or the termination point at the end of the tail. The total length of the keypad flex tail plus the size of the keypad itself is constrained by the maximum size of the printed polyester sheet that can be printed.

Identifying the ProblemThe intent of discussing these problems is to identify the cause of the failures and find a solution. Without knowing the cause of the problem, finding a permanent solution is more difficult. If a part does not stick well to another part, the solution may not be more adhesive. This is a classic engineering materials problem looking for a better solution.

Solution: Transition to Rigid PCBThe best solution involves replacing the parts of the keypad design that caused the problems instead of working around the problems. Epec Engineered Technologies has decades of design and assembly experience with replacing the layered flexible printed membrane with a very thin printed circuit board usually about 0.5 mm (0.020 inches) thick (see figure 3).

Figure 3: High reliability membrane switch with backed rigid printed circuit board.

The printed circuit board is mounted to the metal support plate with high performance acrylic adhesive, similar to a layered flexible membrane keypad. The thermal coefficient of expansion of the printed circuit board laminate is a better match to the metal support plate compared to the polyester/adhesive sandwich. Temperature excursion, shock, and vibration do not cause delamination with the printed circuit board keypad.

The printed circuit keypad assembly can be completed with a graphic overlay, molded rubber keytops, or molded plastic keytops the same as with a printed membrane keypad. The total thickness of the assembly is unaffected as the thin printed circuit board is almost the same thickness as the layered polyester/adhesive.

“Most stress related LED problems do not show up until the product is in the customer’s hands.”

16

Optimal Membrane Switch Design

An overview of some conventional flexible membrane keypads and some unique ways of

implementing them in your application.

41

Alan AtkinsonVP of Dell Storage

A conversation about Dell Compellent's groundbreaking solution and how it will

revolutionize data centers.

RTZReturn to Zero Comic

Using Shift Registers in LED Designs

How shift registers can be used in LED designs to drive multiple LEDs and reduce the size and BOM

of your project.

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Fast Curing Epoxy SystemThe Supreme 3HTND-2GT is a one part, high performance epoxy system that features fast curing perfect for glob top and die attach applications as well as bonding and sealing. It is a multifunctional epoxy system that has a large array of remarkably suitable features such as no mixing, a convenient viscosity, sterling physical proper-ties and very fast cures. It can be applied immediately and effectively to a specific area. This epoxy combines excellent electrical insulation properties and thermal conductivity with top-notch dimensional stability and the capability of withstanding rigorous thermal cycling and shocks...Read More

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Full-featured 802.11 b/g Wi-Fi ModuleThe RN131 is an 802.11 b/g wireless LAN module with ultra-low power design suitable for battery powered applications. With its small form factor and extremely low power consumption, the RN-131 is perfect for mobile wireless applications such as asset monitoring, GPS tracking, and battery sensors. The device has a complete ultra low power embedded TCP/IP solution. The combination of ultra-low power and the abil-ity to wake up, connect to a wireless network, send data, and return to sleep mode in less than 100 milliseconds...Read More

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Since the early 1900s, PID compensators have been one of the most widely used closed loop controllers in industrial applications. However,

the tuning of such controllers is widely considered a difficult art. Talking with anyone who is familiar with tuning often quickly leads to a very distressing discussion about poles, zeros, and margins which makes the casually inclined engineer either stop or, if they are feeling brave (i.e., deadlines closing in), tune the loop intuitively.

{Part 1}

PIDCONTROLLERS

MIXING SIGNALS:An Introduction to

11Visit: eeweb.com

TECH ARTICLE

Since the early 1900s, PID compensators have been one of the most widely used closed loop controllers in industrial applications. However,

the tuning of such controllers is widely considered a difficult art. Talking with anyone who is familiar with tuning often quickly leads to a very distressing discussion about poles, zeros, and margins which makes the casually inclined engineer either stop or, if they are feeling brave (i.e., deadlines closing in), tune the loop intuitively.

{Part 1}

PIDCONTROLLERS

MIXING SIGNALS:An Introduction to

by Sree HarshaCypress Technologies

12 Visit: eeweb.com

PULSE

“In short, we need a mathematical model which can accurately describe the plant characteristic to be able to design a controller which can meet our criteria of overshoot, speed of rejection, and so on.”

Figure 1. A generic plant

But, in a real world, where do we need them? For example, consider a simple room temperature controller. It can either switch ON to heat the room or switch OFF. The regulator in this case is a simple ON-OFF or Hysteric controller. Since we aren’t too picky about the temperature being a few degrees off, this type of controller works quite well (Figure 2).

Now, say we want a more consistent temperature and have a heating element which can control the amount of heating smoothly; i.e., we have more than just an OFF and ON state. This might be a PWM or some other form of input whose magnitude dictates how much heating is produced by the element.

Figure 3 shows a very simple set of rules which can be coded into any generic microcontroller to get this done. We can even throw in a small tolerance band to make the controller smooth around the desired temperature.

Upon close examination, this flow chart is pretty vague and ‘Increment Control Signal’ can mean either increment by 1% or 10%. Additionally, we know that just because we switch ON the heating element, the temperature doesn’t change instantaneously. In essence, our room has an associated ‘Plant Characteristic’ to it. Trying to change the temperature very fast will just lead us to overshoot or undershoot the required room temperature.

With a little trial and error, however, we will be able to arrive at a point where we can trade-off between how fast the temperature reacts with the amount of overshoot we can tolerate. This works out great for simple systems but sometimes plant characteristics can be nasty.

Figure 3. Basic Increment/Decrement Rule

Figure 2. A simple hysteric controller

Figure 4. Fast Increment vs Slow Increment

Why PID?To begin with, why do we need PID controllers? Yes, yes the textbooks all say that you need them and then give a rather generic diagram similar to the one below:

Most of the time, tuning the loop directly on the real system will give favorable results if done carefully and, very happily, a whole lot of math can be ignored. This is almost exclusively the reason why mathematical tuning still remains a less popular method among engineers. This will be a series of articles which I hope will demystify most of the math without being too dry.

A lot of this material is heavily based off of my discussions with Ross Fosler, who I owe most of my practical knowledge in control theory.

13Visit: eeweb.com

TECH ARTICLE

“In short, we need a mathematical model which can accurately describe the plant characteristic to be able to design a controller which can meet our criteria of overshoot, speed of rejection, and so on.”

Figure 1. A generic plant

But, in a real world, where do we need them? For example, consider a simple room temperature controller. It can either switch ON to heat the room or switch OFF. The regulator in this case is a simple ON-OFF or Hysteric controller. Since we aren’t too picky about the temperature being a few degrees off, this type of controller works quite well (Figure 2).

Now, say we want a more consistent temperature and have a heating element which can control the amount of heating smoothly; i.e., we have more than just an OFF and ON state. This might be a PWM or some other form of input whose magnitude dictates how much heating is produced by the element.

Figure 3 shows a very simple set of rules which can be coded into any generic microcontroller to get this done. We can even throw in a small tolerance band to make the controller smooth around the desired temperature.

Upon close examination, this flow chart is pretty vague and ‘Increment Control Signal’ can mean either increment by 1% or 10%. Additionally, we know that just because we switch ON the heating element, the temperature doesn’t change instantaneously. In essence, our room has an associated ‘Plant Characteristic’ to it. Trying to change the temperature very fast will just lead us to overshoot or undershoot the required room temperature.

With a little trial and error, however, we will be able to arrive at a point where we can trade-off between how fast the temperature reacts with the amount of overshoot we can tolerate. This works out great for simple systems but sometimes plant characteristics can be nasty.

Figure 3. Basic Increment/Decrement Rule

Figure 2. A simple hysteric controller

Figure 4. Fast Increment vs Slow Increment

Why PID?To begin with, why do we need PID controllers? Yes, yes the textbooks all say that you need them and then give a rather generic diagram similar to the one below:

Most of the time, tuning the loop directly on the real system will give favorable results if done carefully and, very happily, a whole lot of math can be ignored. This is almost exclusively the reason why mathematical tuning still remains a less popular method among engineers. This will be a series of articles which I hope will demystify most of the math without being too dry.

A lot of this material is heavily based off of my discussions with Ross Fosler, who I owe most of my practical knowledge in control theory.

14 Visit: eeweb.com

PULSE

Figure 5: Some typical Plant Characteristics

For example in Figure 5, the last case is a particularly interesting one, where the plant initially swings in the reverse direction you want to control! Trying to control such systems with a simple rule set can turn into a nightmare for the engineer dealing with it.

In theory, the generic rules associated with the simple increment/decrement rule can work with any system as long as your desired setpoint is a DC value. Only, that the speed at which you reach the desired settling point might be much slower than what you actually need. This is a key point given that rejecting disturbances is fundamental to all closed loop systems. For example, a voltage spike due to a sudden variation in the input voltage or a sudden drop in load can be unacceptable beyond a short period for the devices powered by it.

In short, we need a mathematical model which can accurately describe the plant characteristic to be able to design a controller which can meet our criteria of overshoot, speed of rejection, and so on. Specifically, the above two terms are more formally called as Phase Margin and Bandwidth.

In addition, being able to design a controller on paper will provide an excellent starting point on what the control parameters and will save a whole lot of time spent on tweaking the PID loop.

In part two, I’ll show how to understand plant characteristics using Bode Plots and specifically how to associate a plot with its time response.

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Membrane Switch Design

By Paul KnupkeEpec Engineered Technologies

One style of low-profile keypad

assembly is the conventional

flexible membrane keypad

where the switch circuitry is screen-

printed. Silver conductive polymer inks

are printed onto 1.25 mm (0.005 inches)

polyester sheets. Two opposing polyester

circuit layers are separated by a thin

adhesive/polyester layer with a hole at

the switch location. Finger pressure at

the switch location deforms the front

circuit layer through the spacer hole and

completes the circuit to the bottom circuit

layer. Tactile feel is provided by a metal

snap dome or an embossed dome formed

in a polyester sheet, sometimes called

poly-domes.

For High Reliability Applications

Optimal

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TECH ARTICLE

Membrane Switch Design

By Paul KnupkeEpec Engineered Technologies

One style of low-profile keypad

assembly is the conventional

flexible membrane keypad

where the switch circuitry is screen-

printed. Silver conductive polymer inks

are printed onto 1.25 mm (0.005 inches)

polyester sheets. Two opposing polyester

circuit layers are separated by a thin

adhesive/polyester layer with a hole at

the switch location. Finger pressure at

the switch location deforms the front

circuit layer through the spacer hole and

completes the circuit to the bottom circuit

layer. Tactile feel is provided by a metal

snap dome or an embossed dome formed

in a polyester sheet, sometimes called

poly-domes.

For High Reliability Applications

Optimal

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Since the flexible printed membrane switch assembly is a polyester sheet and layered adhesive, the

switch assembly is not self-supporting and must be mounted to a rigid support. A common support is a flat metal plate such as aluminum. Large dimension flexible printed membrane switch keypads mounted to metal plates are common in the industry. Larger membrane switches with metal plates can suffer performance and construction integrity problems when used in less than ideal environments.

Performance and Construction Integrity ProblemsThese problems are generally related to engineering materials selection. Flexible screen printed membrane keypads are all based on polyester sheets with printed silver conductors (See figure 1). Polyester is the only common plastic film that has the physical memory to

return to its natural position after finger pressure is applied, released to close, and open the switch contact surfaces. Other than polyester, common plastic films will permanently deform after repeated operation and will not return to the normal open switch position when finger pressure is removed. Polyester is universally used for screen printed flexible membrane switches because it is the only material that works correctly. The pressure sensitive adhesive used in membrane keypads is acrylic adhesive but there are different acrylic adhesives that can be used. Each acrylic adhesive group has its own characteristics based on performance and cost usually aligns with performance. The lower cost acrylic adhesives are used only for the least expensive. The lowest performance keypads used in “throw-away” applications where life and environmental performance are traded for lower cost.

Figure 1: Screen printed polyester membrane switch with silver conductive ink.

Even the best designed and manufactured flexible screen printed membrane keypads can have problems when mounted to metal support plates where the keypads and metal plates have large dimensions.

The culprit is the difference in the thermal coefficient of expansion between the plastic/adhesive membrane keypad sandwich and the metal support plate. With higher or lower temperature excursions from room temperature the difference in expansion rates causes sheer stress at the interface between the membrane keypad’s rear mounting acrylic adhesive and the metal plate. Acrylic adhesive has better peel strength performance than sheer strength. Repeated stress cycles can cause delamination between the membrane keypad and the metal support plate. Once the delamination starts, there is no practical solution or repair.

“Other than polyester, common plastic films will permanently deform after repeated operation and will not return to the normal open switch position when finger pressure is removed.”

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TECH ARTICLE

Since the flexible printed membrane switch assembly is a polyester sheet and layered adhesive, the

switch assembly is not self-supporting and must be mounted to a rigid support. A common support is a flat metal plate such as aluminum. Large dimension flexible printed membrane switch keypads mounted to metal plates are common in the industry. Larger membrane switches with metal plates can suffer performance and construction integrity problems when used in less than ideal environments.

Performance and Construction Integrity ProblemsThese problems are generally related to engineering materials selection. Flexible screen printed membrane keypads are all based on polyester sheets with printed silver conductors (See figure 1). Polyester is the only common plastic film that has the physical memory to

return to its natural position after finger pressure is applied, released to close, and open the switch contact surfaces. Other than polyester, common plastic films will permanently deform after repeated operation and will not return to the normal open switch position when finger pressure is removed. Polyester is universally used for screen printed flexible membrane switches because it is the only material that works correctly. The pressure sensitive adhesive used in membrane keypads is acrylic adhesive but there are different acrylic adhesives that can be used. Each acrylic adhesive group has its own characteristics based on performance and cost usually aligns with performance. The lower cost acrylic adhesives are used only for the least expensive. The lowest performance keypads used in “throw-away” applications where life and environmental performance are traded for lower cost.

Figure 1: Screen printed polyester membrane switch with silver conductive ink.

Even the best designed and manufactured flexible screen printed membrane keypads can have problems when mounted to metal support plates where the keypads and metal plates have large dimensions.

The culprit is the difference in the thermal coefficient of expansion between the plastic/adhesive membrane keypad sandwich and the metal support plate. With higher or lower temperature excursions from room temperature the difference in expansion rates causes sheer stress at the interface between the membrane keypad’s rear mounting acrylic adhesive and the metal plate. Acrylic adhesive has better peel strength performance than sheer strength. Repeated stress cycles can cause delamination between the membrane keypad and the metal support plate. Once the delamination starts, there is no practical solution or repair.

“Other than polyester, common plastic films will permanently deform after repeated operation and will not return to the normal open switch position when finger pressure is removed.”

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Mounted LED ConcernsSheer stress, vibration, or shock can take a toll on another part of the screen printed membrane keypad. Many membrane keypads incorporate surface mounted LEDs within the membrane sandwich. Printed silver circuits and polyester cannot tolerate soldering temperatures. LEDs are attached to the printed silver circuits with a small amount of silver-filled conductive epoxy.

In a perfect world, attaching and connecting LEDs to printed silver circuits with conductive epoxy sounds like a good idea. However, one of the inherent problems with polyester film used in flexible membrane switches is that the peel strength adhesion of hard coat texture inks, graphic ink, or silver-filled ink for circuit conductors is less than desired.

LED failures can occur when stress fractures transpire between the silver ink and the polyester at the LED location or along the silver ink conductor next to the LED. The failure starts to occur as a stress crack which may not cause an open circuit right away. When additional stresses are applied during temperature excursion, shock, vibration, intermittent, open circuits can develop causing the LED to be inoperative. Unfortunately there is no practical repair option.

These LED failures can occur even when the flexible membrane is mounted to a metal support plate. Imagine the reliability problems that can be initiated when LEDs are mounted in unsupported

Figure 2: Standard membrane switch stack-up.

flexible membrane keypads. Unsupported keypads are easily stressed during handling when removed from the shipping box, inspected, inventoried, and kitted for an Original Equipment Manufacturer (OEM) assembly line. Applied stresses may not cause any immediate problems. Most stress related LED problems do not show up until the product is in the customer’s hands. The later the failure is detected, the higher the total cost is to repair or replace.

Flexible membrane keypads include a flex tail that is part of the same polyester sheet that contains the circuit conductors in the polyester/adhesive keypad sandwich. Creasing, tearing, abrasion or vibration can easily damage the flex tail or the termination point at the end of the tail. The total length of the keypad flex tail plus the size of the keypad itself is constrained by the maximum size of the printed polyester sheet that can be printed.

Identifying the ProblemThe intent of discussing these problems is to identify the cause of the failures and find a solution. Without knowing the cause of the problem, finding a permanent solution is more difficult. If a part does not stick well to another part, the solution may not be more adhesive. This is a classic engineering materials problem looking for a better solution.

Solution: Transition to Rigid PCBThe best solution involves replacing the parts of the keypad design that caused the problems instead of working around the problems. Epec Engineered Technologies has decades of design and assembly experience with replacing the layered flexible printed membrane with a very thin printed circuit board usually about 0.5 mm (0.020 inches) thick (see figure 3).

Figure 3: High reliability membrane switch with backed rigid printed circuit board.

The printed circuit board is mounted to the metal support plate with high performance acrylic adhesive, similar to a layered flexible membrane keypad. The thermal coefficient of expansion of the printed circuit board laminate is a better match to the metal support plate compared to the polyester/adhesive sandwich. Temperature excursion, shock, and vibration do not cause delamination with the printed circuit board keypad.

The printed circuit keypad assembly can be completed with a graphic overlay, molded rubber keytops, or molded plastic keytops the same as with a printed membrane keypad. The total thickness of the assembly is unaffected as the thin printed circuit board is almost the same thickness as the layered polyester/adhesive.

“Most stress related LED problems do not show up until the product is in the customer’s hands.”

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TECH ARTICLE

Mounted LED ConcernsSheer stress, vibration, or shock can take a toll on another part of the screen printed membrane keypad. Many membrane keypads incorporate surface mounted LEDs within the membrane sandwich. Printed silver circuits and polyester cannot tolerate soldering temperatures. LEDs are attached to the printed silver circuits with a small amount of silver-filled conductive epoxy.

In a perfect world, attaching and connecting LEDs to printed silver circuits with conductive epoxy sounds like a good idea. However, one of the inherent problems with polyester film used in flexible membrane switches is that the peel strength adhesion of hard coat texture inks, graphic ink, or silver-filled ink for circuit conductors is less than desired.

LED failures can occur when stress fractures transpire between the silver ink and the polyester at the LED location or along the silver ink conductor next to the LED. The failure starts to occur as a stress crack which may not cause an open circuit right away. When additional stresses are applied during temperature excursion, shock, vibration, intermittent, open circuits can develop causing the LED to be inoperative. Unfortunately there is no practical repair option.

These LED failures can occur even when the flexible membrane is mounted to a metal support plate. Imagine the reliability problems that can be initiated when LEDs are mounted in unsupported

Figure 2: Standard membrane switch stack-up.

flexible membrane keypads. Unsupported keypads are easily stressed during handling when removed from the shipping box, inspected, inventoried, and kitted for an Original Equipment Manufacturer (OEM) assembly line. Applied stresses may not cause any immediate problems. Most stress related LED problems do not show up until the product is in the customer’s hands. The later the failure is detected, the higher the total cost is to repair or replace.

Flexible membrane keypads include a flex tail that is part of the same polyester sheet that contains the circuit conductors in the polyester/adhesive keypad sandwich. Creasing, tearing, abrasion or vibration can easily damage the flex tail or the termination point at the end of the tail. The total length of the keypad flex tail plus the size of the keypad itself is constrained by the maximum size of the printed polyester sheet that can be printed.

Identifying the ProblemThe intent of discussing these problems is to identify the cause of the failures and find a solution. Without knowing the cause of the problem, finding a permanent solution is more difficult. If a part does not stick well to another part, the solution may not be more adhesive. This is a classic engineering materials problem looking for a better solution.

Solution: Transition to Rigid PCBThe best solution involves replacing the parts of the keypad design that caused the problems instead of working around the problems. Epec Engineered Technologies has decades of design and assembly experience with replacing the layered flexible printed membrane with a very thin printed circuit board usually about 0.5 mm (0.020 inches) thick (see figure 3).

Figure 3: High reliability membrane switch with backed rigid printed circuit board.

The printed circuit board is mounted to the metal support plate with high performance acrylic adhesive, similar to a layered flexible membrane keypad. The thermal coefficient of expansion of the printed circuit board laminate is a better match to the metal support plate compared to the polyester/adhesive sandwich. Temperature excursion, shock, and vibration do not cause delamination with the printed circuit board keypad.

The printed circuit keypad assembly can be completed with a graphic overlay, molded rubber keytops, or molded plastic keytops the same as with a printed membrane keypad. The total thickness of the assembly is unaffected as the thin printed circuit board is almost the same thickness as the layered polyester/adhesive.

“Most stress related LED problems do not show up until the product is in the customer’s hands.”

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Figure 4: Membrane switch with rigid printed circuit board stack-up.

Additional Benefits of Using a Rigid Circuit Board in Your Design1. Additional electronic parts can be

incorporated into the keypad assembly.

2. Surface mounted LEDs can be directly soldered to the printed circuit board, thereby eliminating potential intermittent or open LED circuits caused by stress.

3. Keypad interconnections to the application’s electronics are greatly expanded as a wide variety of connectors can be soldered on the rear surface of the printed circuit board through cutouts in the metal support plate.

4. Connectors can be high density, through-hole, surface-mounted, polarized, latching, or shielded.

5. Electronic components such as resistors, capacitors, diodes, and even integrated circuits can also be mounted to the rear side of the printed circuit.

Determining CostNow that doors of keypad design latitude have been open with expanded selection of electronic components offering reliable soldered electrical joints and much greater reliability, we can look at the last major benefit—cost.

A single printed circuit board replaces several labor intensive manufacturing steps in manufacturing flexible printed membrane keypads. Each of the polyester layers require at least one screen printing operation for the conductive silver ink and generally another printing operation for UV dielectric on the flex tail.

Each polyester printed sheet requires profiling the shape of the keypad and flex tail by steel rule die cutting, knife cutting, or laser cutting. The spacer layer between the polyester circuit layers also requires cutting. Finally, the polyester circuit layers and the spacer layer need to be assembled and laminated together.

Compared to the material and labor needed to fabricate the layered polyester/adhesive membrane, the printed circuit board is no more expensive and usually less expensive.

SummaryIn summary, the causes of poor reliability in conventional flexible silver printed membrane keypads have been identified and a good solution has been advanced.

Along with solving the initial reliability problem of flexible printed membrane keypads in mundane environments, using a thin printed circuit board in place of the layered printed polyester/adhesive provides vastly improved interconnection choices.

Incorporating other electronic components in the keypad is also comparable or lower total cost. The improved reliability using a thin printed circuit board in keypads allows the improved user interface keypad to be used in high reliability and harsh environments with improved overall system design, without increasing the cost.

“A single printed circuit board replaces several labor intensive manufacturing steps in manufacturing flexible printed membrane keypads.”

“The improved reliability using a thin printed circuit board in keypads allows the improved user interface keypad to be used in high reliability and harsh environments with improved overall system design, without increasing the cost.”

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TECH ARTICLE

Figure 4: Membrane switch with rigid printed circuit board stack-up.

Additional Benefits of Using a Rigid Circuit Board in Your Design1. Additional electronic parts can be

incorporated into the keypad assembly.

2. Surface mounted LEDs can be directly soldered to the printed circuit board, thereby eliminating potential intermittent or open LED circuits caused by stress.

3. Keypad interconnections to the application’s electronics are greatly expanded as a wide variety of connectors can be soldered on the rear surface of the printed circuit board through cutouts in the metal support plate.

4. Connectors can be high density, through-hole, surface-mounted, polarized, latching, or shielded.

5. Electronic components such as resistors, capacitors, diodes, and even integrated circuits can also be mounted to the rear side of the printed circuit.

Determining CostNow that doors of keypad design latitude have been open with expanded selection of electronic components offering reliable soldered electrical joints and much greater reliability, we can look at the last major benefit—cost.

A single printed circuit board replaces several labor intensive manufacturing steps in manufacturing flexible printed membrane keypads. Each of the polyester layers require at least one screen printing operation for the conductive silver ink and generally another printing operation for UV dielectric on the flex tail.

Each polyester printed sheet requires profiling the shape of the keypad and flex tail by steel rule die cutting, knife cutting, or laser cutting. The spacer layer between the polyester circuit layers also requires cutting. Finally, the polyester circuit layers and the spacer layer need to be assembled and laminated together.

Compared to the material and labor needed to fabricate the layered polyester/adhesive membrane, the printed circuit board is no more expensive and usually less expensive.

SummaryIn summary, the causes of poor reliability in conventional flexible silver printed membrane keypads have been identified and a good solution has been advanced.

Along with solving the initial reliability problem of flexible printed membrane keypads in mundane environments, using a thin printed circuit board in place of the layered printed polyester/adhesive provides vastly improved interconnection choices.

Incorporating other electronic components in the keypad is also comparable or lower total cost. The improved reliability using a thin printed circuit board in keypads allows the improved user interface keypad to be used in high reliability and harsh environments with improved overall system design, without increasing the cost.

“A single printed circuit board replaces several labor intensive manufacturing steps in manufacturing flexible printed membrane keypads.”

“The improved reliability using a thin printed circuit board in keypads allows the improved user interface keypad to be used in high reliability and harsh environments with improved overall system design, without increasing the cost.”

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Dhigh-performance, low-latency, flash storage solutions for

virtually any demanding application.

price advantage over traditional solutions

and performance at the enterprise level. With technologies evolving at a rapid rate, Dell Compellent’s storage solutions have simplified scalability to adapt to the ever-changing demands of the industry.

EEWeb spoke with Alan Atkinson, Vice President and General Manager of Dell Storage, about their unique approach to product development, how the changing demands of data centers will influence product design, and how Cloud computing will revolutionize the storage industry.

Interview with

Alan Atkinson VP & GM of Dell Storage

Dell Compellent

Enterprise-class Performance at the Price of Disk

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INTERVIEW

Dhigh-performance, low-latency, flash storage solutions for

virtually any demanding application.

price advantage over traditional solutions

and performance at the enterprise level. With technologies evolving at a rapid rate, Dell Compellent’s storage solutions have simplified scalability to adapt to the ever-changing demands of the industry.

EEWeb spoke with Alan Atkinson, Vice President and General Manager of Dell Storage, about their unique approach to product development, how the changing demands of data centers will influence product design, and how Cloud computing will revolutionize the storage industry.

Interview with

Alan Atkinson VP & GM of Dell Storage

Dell Compellent

Enterprise-class Performance at the Price of Disk

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“We came up with what I think is a very

clever software implementation that allowed us to utilize

types of flash that had previously not been used for enterprise

storage. ”

type of things; which are all fine, but they come at a tradeoff of either performance or CPU horsepower to do that. We came up with what I think is a very clever software implementation that allowed us to utilize types of flash that had previously not been used for enterprise storage. In doing so, we were able to get to the price performance level that we wanted, and to date, no one has been able to match us.

Data centers are very dynamic in that they have needs that change all the time from the customers. How are you staying in sync with these trends?

It’s interesting—the data center is probably more dynamic than anything I’ve seen since the migration away from the mainframe in the early ‘90s. On one hand you have your traditional IP, and that discussion hasn’t changed all that much. I would say there’s more focus on power and cooling, but it’s not a radically different conversation. Of course, the advent of virtualization has really driven realization much higher than it’s traditionally been. You start to see bottlenecks move to places like storage. Then you start to see a lot of interest in efficiencies with the virtualization of networking and storage and you start putting PCIe and NAND together, which brought networking and storage closer together.

What is Dell’s approach to providing flash storage products to customers?

We really went at it a different way. We asked ourselves; what if you were able to offer flash at a price where you could take all of your data and put it on flash because that’s what a majority of our customers say they want? The problem is they can’t afford it, so we just couldn’t justify the economics of it. The end goal for our new product was to break the price barrier in the industry—that doesn’t necessarily mean that we would be the fastest, but we definitely had performance targets that we wanted to hit. We ended up with a way to let the user put 100% of their data on flash. That’s a very different approach than I’ve seen other vendors take and I think that’s a unique thing for Dell.

If you think about Dell’s pedigree, disrupting the economics of the data center is kind of our sweet spot. Our latest data center disruption is called Fluid Cache. This will essentially be a PCIe NAND offering that’s pretty

differentiated, but that will actually target high-end applications—however, this won’t be the majority of what it will be used for. What we want to do is let you get there if you need to get there, but we also want to be able to offer a usage for flash that’s much broader than what is out there now.

How is this solution unique in the industry?

We saw other vendors coming out with technologically uninteresting products; they essentially do what you would expect them to do—but what most of the other vendors have gone after is speed. We have also seen some vendors go after some specialized workloads, like cloud and QLS—and that’s all fine. But what we really wanted to do was leverage the technology that we had with the Compellent and EqualLogic install base and really go after that larger market. I have yet to meet a customer that wouldn’t like to have flash instead of disk if they could afford it. We saw that as a market opportunity because nobody was going after that area and mostly because to date, the only way to deal with the cost of better flash was to apply technology you need to for compression or those

“What if you were able to offer flash at a price where you could take all of your data and put it

on flash because that’s what a majority of our customers say they want?”

Dell Compellent SC2000

29Visit: eeweb.com

INTERVIEW

“We came up with what I think is a very

clever software implementation that allowed us to utilize

types of flash that had previously not been used for enterprise

storage. ”

type of things; which are all fine, but they come at a tradeoff of either performance or CPU horsepower to do that. We came up with what I think is a very clever software implementation that allowed us to utilize types of flash that had previously not been used for enterprise storage. In doing so, we were able to get to the price performance level that we wanted, and to date, no one has been able to match us.

Data centers are very dynamic in that they have needs that change all the time from the customers. How are you staying in sync with these trends?

It’s interesting—the data center is probably more dynamic than anything I’ve seen since the migration away from the mainframe in the early ‘90s. On one hand you have your traditional IP, and that discussion hasn’t changed all that much. I would say there’s more focus on power and cooling, but it’s not a radically different conversation. Of course, the advent of virtualization has really driven realization much higher than it’s traditionally been. You start to see bottlenecks move to places like storage. Then you start to see a lot of interest in efficiencies with the virtualization of networking and storage and you start putting PCIe and NAND together, which brought networking and storage closer together.

What is Dell’s approach to providing flash storage products to customers?

We really went at it a different way. We asked ourselves; what if you were able to offer flash at a price where you could take all of your data and put it on flash because that’s what a majority of our customers say they want? The problem is they can’t afford it, so we just couldn’t justify the economics of it. The end goal for our new product was to break the price barrier in the industry—that doesn’t necessarily mean that we would be the fastest, but we definitely had performance targets that we wanted to hit. We ended up with a way to let the user put 100% of their data on flash. That’s a very different approach than I’ve seen other vendors take and I think that’s a unique thing for Dell.

If you think about Dell’s pedigree, disrupting the economics of the data center is kind of our sweet spot. Our latest data center disruption is called Fluid Cache. This will essentially be a PCIe NAND offering that’s pretty

differentiated, but that will actually target high-end applications—however, this won’t be the majority of what it will be used for. What we want to do is let you get there if you need to get there, but we also want to be able to offer a usage for flash that’s much broader than what is out there now.

How is this solution unique in the industry?

We saw other vendors coming out with technologically uninteresting products; they essentially do what you would expect them to do—but what most of the other vendors have gone after is speed. We have also seen some vendors go after some specialized workloads, like cloud and QLS—and that’s all fine. But what we really wanted to do was leverage the technology that we had with the Compellent and EqualLogic install base and really go after that larger market. I have yet to meet a customer that wouldn’t like to have flash instead of disk if they could afford it. We saw that as a market opportunity because nobody was going after that area and mostly because to date, the only way to deal with the cost of better flash was to apply technology you need to for compression or those

“What if you were able to offer flash at a price where you could take all of your data and put it

on flash because that’s what a majority of our customers say they want?”

Dell Compellent SC2000

30 Visit: eeweb.com

PULSE

Those are some of the trends in the traditional data center, but I think the more dynamic part of data centers—which is still relatively small but growing very rapidly—is what software defined for a data center. For example, private clouds that could be implemented as a private cloud or just more of a traditional type of on-demand service. That side of the world is very interesting. They tend to like very uniform footprints; they typically deploy things as pods so they become these sorts of building blocks and have dynamic workload changes applied with them. That’s an area we’re pretty excited about because we have a strong presence in server, storage, and networking—all three as well as services and software. We think that gives us a pretty unique advantage.

We try to put together solutions because in that part of the storage world, you don’t have to buy the traditional big storage array, top of the rack switch, a core switch, and so on. It’s a different type of architecture and we think we’re very well positioned there. It’s also an emerging technology, so if you were to compare dollars, you’re going to have a relatively small expenditure in that area. We spend a lot of time thinking about that space and we’re pretty excited about it.

As far as talking to the data centers and getting a feel for the things they’re looking for, how do environmentally friendly solutions come into play with data centers?

Well it’s not just storage; it’s our whole power and cooling footprint. In those cases, I think the trends that we’ve seen lately have been around what flash does for the storage environment. In regards to convergence—if you look at our VRTX product, for example—it has been a real game changer in the economics with power and cooling as well. But on the flash side, where we’ve really seen it, it’s not unusual that we can take 6U—ten times more worth of spindles—and collapse them down into 2U of flash. This is because people aren’t actually using all the data on those spindles and all they really care about is the performance characteristics. As soon as you go to solid state you change that discussion. Again, this is one of those cases where because we got to the current price point, we can now take a lot more spindles out than other vendors can. You can get pretty good rack compression and that obviously comes with a pretty good power and cooling state as well. It’s a lot cheaper not to have to run those motors. We’ve seen that be a pretty interesting benefit of the whole solid-state discussion.

What types of customers are using Compellent solutions?

We are still early on in the game, but I’m seeing deals go down with financials. Financials are very keen on this, which makes sense. They’re probably among the most data center constrained and some of the most performance hungry out there for their applications, so that’s not really surprising. We’re also seeing a lot of interested service providers.

Surprisingly, if we were to cross the other side, we’re getting a lot of general-purpose interest—the kind of customer that is putting out 3 terabytes of storage. If you look at how our customers buy, they buy a combination of performance and capacity. Just the fact that we’re basically at the price point that we were in May for capacity disks you can now buy, as far as performance disks, you can get 15k if you need. They can now buy flash—it’s just a real differentiator in that general-purpose market. It’s the same people that may have kicked the tires before but now they’re going to buy flash instead of disks.

Offering a product is only a portion of the solution here—the rest of it is providing support to your customers around these releases. What types of services does Dell offer to support its data storage products?

We have full professional services, which are one of the service leaders dating back from the Perot acquisition forward. As far as regular support, I think our copilot, which is the compellent support for our organization, is generally recognized as the best in the class support product. We don’t metric our folks on how many cases they close a day or by quantity. They really will stay on the phone with the customer as long as it takes—they’re

“If you look at how our customers buy, they buy a combination of

performance and capacity.”

Dell Compellent SC8000

31Visit: eeweb.com

INTERVIEW

Those are some of the trends in the traditional data center, but I think the more dynamic part of data centers—which is still relatively small but growing very rapidly—is what software defined for a data center. For example, private clouds that could be implemented as a private cloud or just more of a traditional type of on-demand service. That side of the world is very interesting. They tend to like very uniform footprints; they typically deploy things as pods so they become these sorts of building blocks and have dynamic workload changes applied with them. That’s an area we’re pretty excited about because we have a strong presence in server, storage, and networking—all three as well as services and software. We think that gives us a pretty unique advantage.

We try to put together solutions because in that part of the storage world, you don’t have to buy the traditional big storage array, top of the rack switch, a core switch, and so on. It’s a different type of architecture and we think we’re very well positioned there. It’s also an emerging technology, so if you were to compare dollars, you’re going to have a relatively small expenditure in that area. We spend a lot of time thinking about that space and we’re pretty excited about it.

As far as talking to the data centers and getting a feel for the things they’re looking for, how do environmentally friendly solutions come into play with data centers?

Well it’s not just storage; it’s our whole power and cooling footprint. In those cases, I think the trends that we’ve seen lately have been around what flash does for the storage environment. In regards to convergence—if you look at our VRTX product, for example—it has been a real game changer in the economics with power and cooling as well. But on the flash side, where we’ve really seen it, it’s not unusual that we can take 6U—ten times more worth of spindles—and collapse them down into 2U of flash. This is because people aren’t actually using all the data on those spindles and all they really care about is the performance characteristics. As soon as you go to solid state you change that discussion. Again, this is one of those cases where because we got to the current price point, we can now take a lot more spindles out than other vendors can. You can get pretty good rack compression and that obviously comes with a pretty good power and cooling state as well. It’s a lot cheaper not to have to run those motors. We’ve seen that be a pretty interesting benefit of the whole solid-state discussion.

What types of customers are using Compellent solutions?

We are still early on in the game, but I’m seeing deals go down with financials. Financials are very keen on this, which makes sense. They’re probably among the most data center constrained and some of the most performance hungry out there for their applications, so that’s not really surprising. We’re also seeing a lot of interested service providers.

Surprisingly, if we were to cross the other side, we’re getting a lot of general-purpose interest—the kind of customer that is putting out 3 terabytes of storage. If you look at how our customers buy, they buy a combination of performance and capacity. Just the fact that we’re basically at the price point that we were in May for capacity disks you can now buy, as far as performance disks, you can get 15k if you need. They can now buy flash—it’s just a real differentiator in that general-purpose market. It’s the same people that may have kicked the tires before but now they’re going to buy flash instead of disks.

Offering a product is only a portion of the solution here—the rest of it is providing support to your customers around these releases. What types of services does Dell offer to support its data storage products?

We have full professional services, which are one of the service leaders dating back from the Perot acquisition forward. As far as regular support, I think our copilot, which is the compellent support for our organization, is generally recognized as the best in the class support product. We don’t metric our folks on how many cases they close a day or by quantity. They really will stay on the phone with the customer as long as it takes—they’re

“If you look at how our customers buy, they buy a combination of

performance and capacity.”

Dell Compellent SC8000

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proactive either in a box or they’ll perform firmware upgrades, which is an area where we consistently get kudos. That’s been well before my time at Dell, so that goes back to where Compellent was an independent company. We’ve been taking some of the software that powers that and building them EqualLogic as well. Again we’re spending a lot of time talking about family values, if you will, trying to get sort of the best features of all of our product lines across all of our product lines because why not. We own that IP, so why wouldn’t we do that? That’s an area where we really excel.

How would describe the leadership and culture behind Dell’s flash storage solution?

I think it’s a culture of innovation that goes way back. Tiering was basically invented by a few people at Compellent. I know that’s been copied a lot and there’s multiple versions of vendors who would still argue they’re best in class, but because of the way we get virtualization tiering, We really took a step back and said what if we rewrote these tiering algorithms specifically for flash—what could we accomplish and how can we really be disruptive? To us, the design goal that really goes after that market was not specialized. We could have done something like: we just want to make the fastest thing out there and we could have probably pulled it off and I think actually on the PCIE NAND side we’re going to make some pretty exciting announcements in that area.

I think we’ve got we really set out to look at a problem that no on else was really going after and figured out a way to do it. I think that’s a really good team effort between marketing guys and the engineers researched it really well. We know people want flash, we don’t know how to get it to them other than selling it at a loss, which isn’t a great business generally so this is something we’re really excited about. So far it’s been going really well for us.

Flash being the price of disk is really one example of disruptive design. We’re in the midst of a really exciting time in Dell storage. Between August of this year to March 2014, we have 9 product introductions, which is a really remarkable clip of getting products out. They’re all sort of done with that disrupting the data center economic kind of philosophies. That’s not just flash, but that’s also things like the Fluid Cache and also things like data placement at the low end when you really want to optimize capacity size and all through the lens of how can we be disrupting by offering more for less. I think that is the general design philosophy that we have.

“Flash being the price of disk is really

one example of disruptive design.

We’re in the midst of a really exciting time

in Dell storage.”

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by Michael Lyons, NXP Semiconductor

In designs that use LEDs, shifter registers can be very useful. For instance, if the system includes a seven-segment display, a single indicator, or an array of LEDs that form a grid or

panel, a standard 8-bit shift register can be used to allow a low pin-count microcontroller to drive multiple LEDs.

Using

in LED Designsto Reduce Size and BOM

SHIFT REGISTERS

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TECH ARTICLE

by Michael Lyons, NXP Semiconductor

In designs that use LEDs, shifter registers can be very useful. For instance, if the system includes a seven-segment display, a single indicator, or an array of LEDs that form a grid or

panel, a standard 8-bit shift register can be used to allow a low pin-count microcontroller to drive multiple LEDs.

Using

in LED Designsto Reduce Size and BOM

SHIFT REGISTERS

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Figure 1 gives an example. A single 5V 74HC595 shift register, with serial inputs and serial or parallel outputs, provides I/O expansion for the microcontroller. Serial data is applied to the serial input of the 74HC595 and clocked in via the input clock. Once the 74HC595 is loaded, the output clock applies the data to the storage register and to the parallel and serial outputs. External drivers, controlled by the 74HC595, then activate the corresponding LEDs.

Using the 74HC595 for I/O expansion means that it takes only three MCU control pins to drive up to eight LEDs. Reducing the number of control pins makes it possible to use an MCU with a lower pin count, and that can yield a smaller, more cost-effective design.

Also, because the 74HC595 includes a serial output, several devices can be cascaded together. Figure 2 gives the layout.

Figure 1. An 8-bit 74HC595 shift register driving multiple LEDs

Now, with the cascading, the same three pins on the microcontroller can be used to control up to 16 or 24 LEDs instead of just eight. The ability to cascade shift registers can reduce the total number of microcontrollers needed in the design, and that can help lower costs and reduce size, too.

In some cases, a 5 V, 8-bit register like the 74HC595 can be used to drive LEDs directly. This works best when the LEDs are specified for relatively low voltage and forward current. LEDs that operate with voltages higher than 6 V or require forward current that exceeds 70 mA will typically require an external driver.

Open-drain OutputsAdding open-drain outputs to the shift register creates a single-chip solution that eliminates the need for an external driver. This can yield significant reductions in the bill of materials, since each output of the shift register can drive the LEDs directly.

Figure 3. Output schematic for shift register with open-drain outputs

Figure 4. Output schematic for shift register with open-drain outputsFigure 2. Cascading 74HC595 devices to drive more LEDs

Figure 3 gives the output schematic for one such device, the NPIC6C596A LED driver from NXP, which combines shift register functions similar to a 74HC595 with a high-voltage (HV) MOSFET driver.

Replacing the 74HC595 with the NPIC6C596A eliminates the need for external drivers, creating a design that is more compact and has a lower bill of materials.

NPIC6C devices have open-drain outputs that are tolerant to 33 V. Each output is designed to sink 100 mA and there is no limit on ground current. All the outputs can actively sink 100 mA simultaneously. The outputs include current-limiting circuitry, which sets a 250 mA maximum on the sinkable current, and each output also includes thermal protection. Having

The ability to cascade shift registers can reduce the total number of microcontrollers

needed in the design, and that can help lower costs and reduce size, too.

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TECH ARTICLE

Figure 1 gives an example. A single 5V 74HC595 shift register, with serial inputs and serial or parallel outputs, provides I/O expansion for the microcontroller. Serial data is applied to the serial input of the 74HC595 and clocked in via the input clock. Once the 74HC595 is loaded, the output clock applies the data to the storage register and to the parallel and serial outputs. External drivers, controlled by the 74HC595, then activate the corresponding LEDs.

Using the 74HC595 for I/O expansion means that it takes only three MCU control pins to drive up to eight LEDs. Reducing the number of control pins makes it possible to use an MCU with a lower pin count, and that can yield a smaller, more cost-effective design.

Also, because the 74HC595 includes a serial output, several devices can be cascaded together. Figure 2 gives the layout.

Figure 1. An 8-bit 74HC595 shift register driving multiple LEDs

Now, with the cascading, the same three pins on the microcontroller can be used to control up to 16 or 24 LEDs instead of just eight. The ability to cascade shift registers can reduce the total number of microcontrollers needed in the design, and that can help lower costs and reduce size, too.

In some cases, a 5 V, 8-bit register like the 74HC595 can be used to drive LEDs directly. This works best when the LEDs are specified for relatively low voltage and forward current. LEDs that operate with voltages higher than 6 V or require forward current that exceeds 70 mA will typically require an external driver.

Open-drain OutputsAdding open-drain outputs to the shift register creates a single-chip solution that eliminates the need for an external driver. This can yield significant reductions in the bill of materials, since each output of the shift register can drive the LEDs directly.

Figure 3. Output schematic for shift register with open-drain outputs

Figure 4. Output schematic for shift register with open-drain outputsFigure 2. Cascading 74HC595 devices to drive more LEDs

Figure 3 gives the output schematic for one such device, the NPIC6C596A LED driver from NXP, which combines shift register functions similar to a 74HC595 with a high-voltage (HV) MOSFET driver.

Replacing the 74HC595 with the NPIC6C596A eliminates the need for external drivers, creating a design that is more compact and has a lower bill of materials.

NPIC6C devices have open-drain outputs that are tolerant to 33 V. Each output is designed to sink 100 mA and there is no limit on ground current. All the outputs can actively sink 100 mA simultaneously. The outputs include current-limiting circuitry, which sets a 250 mA maximum on the sinkable current, and each output also includes thermal protection. Having

The ability to cascade shift registers can reduce the total number of microcontrollers

needed in the design, and that can help lower costs and reduce size, too.

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these protections means the NPIC6C596A device can be used to drive a wider range of LEDs than the 74HC595, including LEDs that operate at higher voltages and with higher forward current.

Protection featuresFigure 5 shows the behavior of the current-limiting circuitry on the open-drain outputs of the NPIC6596A. The circuitry limits the maximum current each output can sink. As the drain voltage increases, the drain source current decreases. This protects the outputs and the components they are driving. At 25 °C, the output clamp is typically activated when the drain source current is 250 mA.

Figure 6 shows how the open-drain outputs of the NPIC6C596A provide thermal protection. The clamp current is inversely proportional to temperature. As the temperature increases, the output resistance increases, thus limiting the drain source current and preventing damage to the output and the components it drives. At 25 °C, the output typically limits the drain source current to 120 mA.

Figure 5. Current-limiting behavior in NPIC6C596A

Figure 6. Thermal protection in NPIC6C596A

Multiple OptionsTable 1 shows the NPIC6C LED drivers available from NXP. The NPIC6C596 and the NPIC6C596A are 8-bit solutions, while the NPIC6C4894 is a 12-bit solution. All include a serial output for cascading. Data is propagated through the shift register on the rising edge of the input clock. With the NPIC6C595 and the NPIC6C4894, the same rising edge is used to clock data to the serial output QS. The NPIC6C596 and NPIC6C596A delay the serial output to the next falling edge of the input clock. The delay provides a longer data hold time, which improves timing margin and makes it easier to cascade many shift registers.

As the temperature increases, the output resistance increases, thus limiting the drain

source current and preventing damage to the output and the components it drives.

Type number Format Supply voltage (V)

fmax (MHz) Tamb (°C) QS clock Packages

NPIC6C595 8-bit 4.5 to 5.5 10 -40 to +125 Rise SO16, TSSOP16, DQFN16

NPIC6C596 8-bit 4.5 to 5.5 10 -40 to +125 Fall SO16, TSSOP16, DQFN16

NPIC6C596A 8-bit 2.3 to 5.5 10 -40 to +125 Rise SO16, TSSOP16, DQFN16

NPIC6C4894 12-bit 4.5 to 5.5 10 -40 to +125 Rise SO20, TSSOP20, DQFN20

NPIC6C LED drivers from NXP

The NPIC6C596 and NPIC6C4894 can be used between 4.5 and 5.5 V, making them suitable for 5.0 V control logic interfaces. The NPIC6C596A can be used from 2.3 to 5.5 V, so it can be used with 5.0, 3.3, and 2.5 V control logic interfaces. All NPIC6C devices operate from -40 to +125 °C and with an input clock frequency of at least 10 MHz.

Table 1. NPIC6C LED drivers from NXP

The delay provides a longer data hold time, which improves timing

margin and makes it easier to cascade many shift registers.

39Visit: eeweb.com

TECH ARTICLE

these protections means the NPIC6C596A device can be used to drive a wider range of LEDs than the 74HC595, including LEDs that operate at higher voltages and with higher forward current.

Protection featuresFigure 5 shows the behavior of the current-limiting circuitry on the open-drain outputs of the NPIC6596A. The circuitry limits the maximum current each output can sink. As the drain voltage increases, the drain source current decreases. This protects the outputs and the components they are driving. At 25 °C, the output clamp is typically activated when the drain source current is 250 mA.

Figure 6 shows how the open-drain outputs of the NPIC6C596A provide thermal protection. The clamp current is inversely proportional to temperature. As the temperature increases, the output resistance increases, thus limiting the drain source current and preventing damage to the output and the components it drives. At 25 °C, the output typically limits the drain source current to 120 mA.

Figure 5. Current-limiting behavior in NPIC6C596A

Figure 6. Thermal protection in NPIC6C596A

Multiple OptionsTable 1 shows the NPIC6C LED drivers available from NXP. The NPIC6C596 and the NPIC6C596A are 8-bit solutions, while the NPIC6C4894 is a 12-bit solution. All include a serial output for cascading. Data is propagated through the shift register on the rising edge of the input clock. With the NPIC6C595 and the NPIC6C4894, the same rising edge is used to clock data to the serial output QS. The NPIC6C596 and NPIC6C596A delay the serial output to the next falling edge of the input clock. The delay provides a longer data hold time, which improves timing margin and makes it easier to cascade many shift registers.

As the temperature increases, the output resistance increases, thus limiting the drain

source current and preventing damage to the output and the components it drives.

Type number Format Supply voltage (V)

fmax (MHz) Tamb (°C) QS clock Packages

NPIC6C595 8-bit 4.5 to 5.5 10 -40 to +125 Rise SO16, TSSOP16, DQFN16

NPIC6C596 8-bit 4.5 to 5.5 10 -40 to +125 Fall SO16, TSSOP16, DQFN16

NPIC6C596A 8-bit 2.3 to 5.5 10 -40 to +125 Rise SO16, TSSOP16, DQFN16

NPIC6C4894 12-bit 4.5 to 5.5 10 -40 to +125 Rise SO20, TSSOP20, DQFN20

NPIC6C LED drivers from NXP

The NPIC6C596 and NPIC6C4894 can be used between 4.5 and 5.5 V, making them suitable for 5.0 V control logic interfaces. The NPIC6C596A can be used from 2.3 to 5.5 V, so it can be used with 5.0, 3.3, and 2.5 V control logic interfaces. All NPIC6C devices operate from -40 to +125 °C and with an input clock frequency of at least 10 MHz.

Table 1. NPIC6C LED drivers from NXP

The delay provides a longer data hold time, which improves timing

margin and makes it easier to cascade many shift registers.

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Package Suffix D PW EQ D PW16-pin 16-pin 16-pin 20-pin 20-pin

Package SOTI109-1 SOT403-1 SOT763-1 SOT163-1 SOT-360-1

Width (mm) 6.00 6.40 2.50 10.30 6.4

Length (mm) 9.90 5.00 3.50 12.80 6.50

Height (mm) 1.75 1.10 1.00 2.65 1.10

Pitch (mm) 1.27 0.65 0.50 1.27 0.65

NPIC6C LED drivers are available in industry-standard SO and TSSOP packages, as well as the space-saving DQFN leadless package, which is up to 76 percent smaller than a TSSOP and 40 percent smaller than a QFN. DQFN packages also include a heat sink and are the packages of choice for space-constrained applications that use higher currents. Automotive variants are also available.

Table 2. Package options for NPIC6C LED drivers

ConclusionWhen LEDs are part of the design, shift registers make it possible to use a smaller, less expensive microcontroller. Standard 8-bit shift registers like the 74HC595 are available from a number of suppliers, including NXP. Shift registers that are equipped with open-drain outputs, like the NPIC6C series from NXP, go a step further, because they eliminate the need for external LED drivers. More about the NPIC6C series can be found at http://www.nxp.com/products/logic/family/NPIC/#overview.

When LEDs are part of the design, shift registers make it possible to use a smaller, less expensive microcontroller.

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Package Suffix D PW EQ D PW16-pin 16-pin 16-pin 20-pin 20-pin

Package SOTI109-1 SOT403-1 SOT763-1 SOT163-1 SOT-360-1

Width (mm) 6.00 6.40 2.50 10.30 6.4

Length (mm) 9.90 5.00 3.50 12.80 6.50

Height (mm) 1.75 1.10 1.00 2.65 1.10

Pitch (mm) 1.27 0.65 0.50 1.27 0.65

NPIC6C LED drivers are available in industry-standard SO and TSSOP packages, as well as the space-saving DQFN leadless package, which is up to 76 percent smaller than a TSSOP and 40 percent smaller than a QFN. DQFN packages also include a heat sink and are the packages of choice for space-constrained applications that use higher currents. Automotive variants are also available.

Table 2. Package options for NPIC6C LED drivers

ConclusionWhen LEDs are part of the design, shift registers make it possible to use a smaller, less expensive microcontroller. Standard 8-bit shift registers like the 74HC595 are available from a number of suppliers, including NXP. Shift registers that are equipped with open-drain outputs, like the NPIC6C series from NXP, go a step further, because they eliminate the need for external LED drivers. More about the NPIC6C series can be found at http://www.nxp.com/products/logic/family/NPIC/#overview.

When LEDs are part of the design, shift registers make it possible to use a smaller, less expensive microcontroller.

Radar Regret

On to the Next - Pt. 5

Curious Competition - Pt. 4