page 1 designing small, simple and efficient dc to dc converters andy cowell applications manager...

Designing Small, Simple and Efficient DC to DC Converters Andy Cowell Applications Manager Asia Feb 2004

MICRELS DC to DC Converters u SMALL SIMPLE and EFFICIENENT u Small l Any DC to DC converter must be as small as possible for the given application u Simple l The DC to DC converter must use as few external components as possible, without sacrificing performance u Efficient l The DC to DC converter must be highest efficiency to minimize any losses

The Issues making a DC-DC Small u The biggest component of a DC to DC converter are the Inductor L, and the Capacitance C u Increasing the switching frequency decreases the size of L and C, but decreases the Efficiency. u The DC to DC converter must have high speed loop response to keep the output voltage stable under all conditions with a small value of L and C

The Issues Making a DC-DC Simple u To make a DC to DC converter simple all the stability components need to be inside the Integrated Circuit u The DC to DC converter needs to have high loop speeds without any external components to keep the L and C small

u The DC to DC converter needs to have a high switching frequency to keep the L and the C small u As the switching Frequency increases the switching losses increase, making it less efficient l Note Switching Power Loss in a MOSFET device used in most DC to DC converters, Is proportional to Mosfet gate charge,Q, x Gate Voltage, Vgs, x Frequency, f u A new drive scheme is needed to minimize switching losses The Issues Making a DC-DC Efficient

Introducing MIC2202

2.3V to 5.5V Input Output down to 0.5V 600mA l Industrys Smallest Output Components l Ultra-fast transient response l Over 95% efficient l Tiny MSOP-10 and 3mm x 3mm MLF-10L 2.2 H 1F1F 2.2 F PWM Regulator with Worlds Smallest LC 2MHz PWM Synchronous Buck Regulator

MIC2202 Benefits u Small Tiny 2.2 H inductor and 1 F capacitor (or visa-versa, 1 H inductor and 2.2 F capacitor!! ) l Few external components l 3mm x 3mm MLF package has same pcb area as SOT23 n 4x better thermal performance than SOT23 u Low Noise l No variable frequency modes of operation n MIC2202 always operates in fixed frequency PWM mode l Ideal for noise sensitive applications n RF and high speed communications systems

MIC2202 Benefits u FAST! l Up to 500KHz closed loop band width n Fast transient response allows smaller C OUT l Ideal for applications that need fastest response n DAC-controlled V OUT applications such as CDMA RF Power u Efficient l >95% efficient l Proprietary gate drive minimizes shoot-through current

How the MIC2202 can use small values of L and C u The 2Mhz switching frequency keeps the L and C Low. u To Reduce the L and C to Only 2.2uH and 1uF output Capacitor, a very high loop bandwidth was required. u Traditionally a tantalum output capacitor is required to add an extra zero into the loop to help stabilize. u The MIC2202 uses a 1uF ceramic output capacitor to reduce size A new compensation scheme is needed to achieve high stable bandwidths

MIC2202 Ultra high Bandwidth loop compensation ULTRA HIGH BW

MIC2202 Performance: L = 2.2 H, C OUT = 1 F Excellent Load Transient Response Switching Waveforms

High Efficiency with MIC2204 High Efficient drive scheme reduces switching losses

MIC2202 Efficiency

MIC2202 Inductor Selection versus Efficiency 2.2 H is optimal inductor value for small size and high efficiency MIC2202 works with as low as 1 H inductor for the smallest size Up to 4.7 H inductor for reduced ripple current and higher light load efficiency.

MIC2202 Eval Boards u 2 evaluation boards are available: l MIC2202BMM EV (MSOP-10 package) l MIC2202BML EV (3x3 MLF package) V IN V OU T 1cm x 1.3cm pcb area

MIC2202 Applications u 802.11 WLAN power supply u Camera / video chip power l Cellular phones l PDAs l Digital cameras u CDMA Dynamic V OUT RF Power Amp power supply u Wireless and DSL modems u Storage drives u CD/DVD ROM power u PHY core and I/O power supply u ASIC / FPGA / DSP / CPU power supply u Portable applications

A High Power Guide to the World of Low Power DC to DC Converters Andy Cowell Applications Manager Asia Email [email protected]@micrel.com Tel +64 6 378 9799 WWW.MICREL.COM

Technical Sheet Buck Converter Buck - Technical Sheet

Selector Guides Micrel Part number. Feature Synchrous Buck? External Switch(es) required Switching Frequency Input Voltage (Volts DC) Output Current Min Output voltage MIC2202/4 ** Ultra small L and C for up to 600mA out YESNo2 MHz2.7 to 5.5V50mA- 600mA 0.5V MIC2168/9 ** Small size Buck controller YES 1Mhz/500k Hz 3 to 14V500mA-20A0.8V MIC4680/4 ** Small SimpleNO 200kHz4.5-34V1-1.5A1.25V MIC4685 Small SimpleNO 200kHz4.5V-32V3A1.25V MIC2193/4 Low voltage SO-8 controller YES 400Khz2.9V-14V500mA-10A1.25V MIC2183/4 Flexable SO-16 Controller Ics YES 200/400KHz2.9V-14V500mA-10A1.25V MIC2198/9 Utra small High voltage Buck YES 200/400Khz4.5-32V500mA-20A1V MIC2182 Controller with light load mode YES 200Khz4.5V to 32V500mA to 20A 1.25V ** Most popular

MIC2168/9 Small, Simple DC/DC Controllers

u 3V IN to 14.5V IN u V OUT down to 0.8V u 500KHz fixed frequency PWM (MIC2169) u 1MHz fixed frequency PWM (MIC2168) u Up to 97% efficiency u No sense resistor u Output over-voltage protection u Adaptive gate drive MIC2168/9 Simple Synchronous Buck Controllers V IN V OU T R SET

u Wide 3V to 14.5 operating range l Works from 3.3V, 5V, and 12V power busses l Internal bootstrap allows single supply operation l Other solutions require split supply operation u V OUT range 0.8V to 12V; I OUT up to 20A l Powers the latest ICs u Adaptive gate drive l Allows up to 97% efficiency l Prevents shoot-through current u High-side n-channel MOSFET current sensing l No current-sense resistor saves cost and efficiency MIC2168/9 Features

u Dual mode current limit allows fastest recovery time l Hard current limit until V OUT drops ~16% l Hiccup current limit after V OUT drops below 16% (output short-circuit protection) u Output over-voltage protection l Protects system downstream in fault conditions u Hysteretic transient recovery mode l Allows ultra-fast transient response u Internal soft-start l Reduces in-rush current u Dual function COMP / EN pin l Pull this pin to ground for low power shutdown mode u Flexible architecture l Tantalum capacitor capable for most applications l All-ceramic capacitor capable for smallest size l Electrolytic capacitor capable for lowest cost MIC2168/9 Features

u Point-of-Load DC/DC Conversion u Telecom/Networking/Datacom systems u DSP / CPU / FPGA / ASIC power supplies u Set top boxes u Graphics Cards u LCD Power Supplies u Cable modems u HDD and tape drives u DC/DC SIP modules MIC2168/9 Applications

u MIC2168 (1MHz) l Use for smallest size applications l 1MHz operation allows smaller external inductor l The trade off with higher frequency is slightly less efficiency (up to ~3- 5%) and lower output current l MIC2168 is optimal for < ~5A applications u MIC2169 (500KHz) l Use for highest current applications that require the most efficiency MIC2168 versus MIC2169

u Typical dc/dc controllers sacrifice efficiency by having a long fixed dead time between the high- and low-side MOSFET drivers to prevent shoot-through current. The dead time needs to account for maximum MOSFET gate capacitance. Though it prevents shoot-through, efficiency is lost during the low-side MOSFET parasitic diode or external Schottky diode conduction time. u The MIC2168/9 self-adjusts the dead-time from 30ns to 100ns to maximize efficiency and prevent shoot-through MIC2169 Proprietary Adaptive Gate Drive V IN V OUT No Shoot-Through!

u Turn on characteristic, V OUT rise time: MIC2169 Internal Soft Start 2ms rise time Reduces in- rush current

u Output OVP protects load in fault conditions l eg: solder-bridge in assembly, or if high-side NFET fails short u Low-side NFET turns on during output OVP conditions l Blows input fuse to protect the expensive downstream load MIC2169 Output Over-Voltage Protection OVP Test Inductor Current sinking 1A OVP Test Circuit: Switch High Voltage to MIC2169 Output (1A current limited for benign test)

MIC2169 All Ceramic Capacitor Circuit V IN 5V V OUT 3.3V 4A

MIC2169 All Ceramic Circuit Performance

MIC2169 Ceramic Circuit Bode Plot STABLE! 54 Phase Margin 29kHz cross-over frequency

MIC2169 7A Eval Board TOP BOTTOM MIC2169 V OUT selector jumpers N-Channel MOSFETs V OUT V IN C IN C OUT Inductor u Available on on-line sample order system 1.75 4.5c m 2 5cm

MIC2169 7A General Purpose Eval Board * Light snubbing is required for super low duty cycle applications to maintain accurate current limiting (ex: 12V IN to 1V OUT applications). These components can be removed for applications with higher duty cycle. V IN 5V to 12V V OUT (Jumper Adjustable ) * * Shut Down (optional )

u Eval Board Efficiency MIC2169 Eval Board Performance Eval Board supports 10A with airflow, 7A without. Current is limited by the PCB thermals

MIC2169 Eval Board Bode Plot (12V IN to 3.3V OUT ) STABLE! 64 Phase Margin 26kHz cross-over frequency

Technical Sheet Boost Converter Boost - Technical Sheet

Selector guide- Boost Micrel Part number. Feature Synchrono us Boost? External Switch(es) required Switching Frequency Input Voltage (Volts DC) Output Current Max Output voltage MIC2288 ** Small SOT23 Package, high output power NO 1.2 MHz2.5- 10VUp to 500mA 34V MIC2290 ** 2288 with internal schottky diode YESNO1.2MHz2.5V- 10VUp to 300mA 34V MIC2196 ** Small Simple in SO-8 NOYES400kHz2.9V-14V5A+>50V MIC2171 High power Boost with internal switch NO 100Khz3.0V-40V3A60V MIC2185/6 Flexable SO-16 Controller Ics YES 200/400K Hz 2.9V-14V5A+>50V MIC2145 High Power MSOP- 8 NO 450Khz2.2V-14VUp to 700mA 18V MIC3171/2 High voltage simple SO-8 NO 100Khz3V - 40V500mA60V MIC2141/2 Small SOT23NO 330kHz2.7-16Vto 100mA18V ** Most popular

MIC2288 Boost Regulator OEL Driver u 2.5V to 10V IN u 1.2MHz fixed frequency PWM u >1A switch current u Up to 34V OUT u Tiny 2x2mm MLF-8L and Thin SOT23-5L package options

MIC2288 Boost Regulator L = 10 H C OUT = 10 F

MIC2288 Boost Regulator V OUT

page 1 designing small, simple and efficient dc to dc converters andy cowell applications manager...

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