max17515 5a 2.v to 5.5v inpt higefficienc power...

General DescriptionThe MAX17515 is a fixed-frequency, step-down power module in a thermally efficient system-in-package (SIP) package that operates from a 2.4V to 5.5V input supply voltage and supports output currents up to 5A. The device includes switch-mode power-supply controller, dual n-channel MOSFET power switches, a fully shielded inductor, as well as compensation components. The device supports 0.75V to 3.6V programmable output voltage. The high level of integration significantly reduces design complexity, manu-facturing risks, and offers a true “plug-and-play” power-supply solution, reducing the time to market.The device operates at a fixed 1MHz that requires smaller input and output capacitor size. The internal fixed con-stant gain at the error-amplifier output results in output-voltage positioning with respect to the load current. The fixed internal digital soft-start limits the input inrush cur-rent at startup. The device also operates in pulse-skipping mode at light loads to improve the light-load efficiency.The MAX17515 is available in a thermally enhanced, compact 28-pin, 10mm x 6.5mm x 2.8mm SIP package and can operate over the -40°C to +85°C industrial temperature range.

Applications FPGAandDSPPoint-of-LoadRegulator BaseStationPoint-of-LoadRegulator IndustrialControlEquipment Servers ATEEquipment MedicalEquipment

Benefits and Features CompleteSwitch-ModePowerSupplyinOne

Package 2.4Vto5.5VInputVoltageRange 0.75Vto3.6VProgrammableOutputVoltage AutoSwitchLight-LoadPulse-SkippingMode FaultProtection

• Output Overvoltage Protection • Output Undervoltage Protection • Thermal-Fault Protection • PeakCurrentLimit

EnableInput Upto94%Efficiency Power-GoodOutput Voltage-ControlledInternalSoft-Start High-ImpedanceShutdown <1µAShutdownCurrent PassesEN55022(CISPR22)ClassBRadiatedand

Conducted EMI Standard

Ordering Information appears at end of data sheet.

For related parts and recommended products to use with this part, refer to www.maximintegrated.com/MAX17515.related.

IN

IN

IN

IN

VCC

EN

GND GND GNDPOK

FB

OUT

OUT

OUT

OUT

OUT

OUT

OUT

OUT

PGND

MAX17515

VIN5V

VOUT

1.1V, 5A

VCC

VCC

1kΩ

220µF

22µF

22.1kΩ

PGND

PGND

PGND

PGND

PGND

PGND

47.5kΩ

22µF

MAX17515 5A, 2.4V to 5.5V Input, High-Efficiency Power Module

19-6711; Rev 0; 6/13

Typical Application Circuit

EVALUATION KIT AVAILABLE

INtoPGND .............................................................-0.3V to +6VVCCtoGND ............................................................-0.3V to +6VVCCtoIN .................................................................-0.3V to +6VENtoGND ..............................................................-0.3V to +6VFB,POKtoGND ...................................... -0.3V to (VCC + 0.3V)OUT,EP3toGND ......................................-0.6V to (VIN + 0.3V)PGNDtoGND ......................................................-0.3V to +0.3VEP1toGND..........................................................-0.3V to +0.3V

EP2toPGND ......................................... -0.3V to + (VIN + 0.3V)EP2toGND............................................ -0.6V to + (VIN + 0.3V)ContinuousPowerDissipation(TA = +70°C)

28-Pin SIP (derate 37mW/°C above +70°C) ............2000mW OperatingTemperatureRange ........................... -40°C to +85°CJunction Temperature ......................................................+125°CStorageTemperatureRange ............................ -55°C to +150°CLeadTemperature(soldering,10s) .................................+245°C

SIP Junction-to-AmbientThermalResistance(qJA)...........25°C/W Junction-to-CaseThermalResistance(qJC) .................6°C/W

(Note 1)

(VIN = VCC = VEN = 5V,-40°C<TA<+85°C.TypicalvaluesareatTA = +25°C, unless otherwise noted.) (Typical Application Circuit) (Note2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITSINPUT SUPPLY (VIN)

INInputVoltageRange VIN2.4 5.5

VVIN = VCC 4.5 5.5

INUndervoltageThreshold Risingedge(100mVhysteresis) 2.05 2.19 2.4 V

INStandbySupplyCurrent IQ VIN = VCC = 4.5V, no load 1 5.5 μA

VCC SUPPLYVCCInputVoltageRange VCC 4.5 5.5 V

VCC Undervoltage Threshold Risingedge(160mVhysteresis) 3.9 4.2 4.5 V

VCC Shutdown Supply Current IVCC_SHDEN=GND,POKunconnected,measuredat VCC, TA = +25°C 0.1 1.0 μA

VCC Supply Current IVCCRegulatorenabled,noload,noswitching(VFB = 1V) 62 135 μA

OUTPUTOutput Voltage Programmable Range VOUT

VIN = VCC = 5.2V, ILOAD = 2A(see derating curve for VOUT > 2.5V) 0.754 3.6 V

UnityGainOutput-VoltageTolerance/FBaccuracy FB=OUT,noload 0.750 0.770 0.786 V

FBLoadRegulationAccuracy(RDROOP) 2A<IOUT<5A,FB=OUT -7.5 -4.4 -1 mV/A

FBLineRegulationAccuracy FB=OUT,noload,2.4V<VIN <5.5V 1.253 4.5 mV/V

FBInputBiasCurrent TA=-40°Cto+85°C(Note3) -0.1 -0.015 +0.1 μA


www.maximintegrated.com Maxim Integrated 2

Note 1: PackagethermalresistanceswereobtainedusingthemethoddescribedinJEDECspecificationJESD51-7,usingafour-layerboard. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.

Absolute Maximum Ratings

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

Package Thermal Characteristics

Electrical Characteristics

(VIN = VCC = VEN = 5V,-40°C<TA<+85°C.TypicalvaluesareatTA = +25°C, unless otherwise noted.) (Typical Application Circuit) (Note2)

Note 2: Limitsare100%testedatTA = +25°C. Maximum and minimum limits are guaranteed by design and characterization over temperature.

Note 3: DesignguaranteedbyATEcharacterization.Limitsarenotproductiontested.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITSAverageOutputCurrentLimit VIN = 5V 5 8 AEFFICIENCY

EfficiencyVIN = 5V, VOUT = 1.1V, IOUT = 2A 86

%VIN = 5V, VOUT = 1.1V, IOUT = 5A 77

SWITCHING FREQUENCYSwitching Frequency fSW 0.9 1 1.1 MHzSOFT-STARTSoft-StartRampTime tSS 1.79 ms

Soft-StartFaultBlankingTime tSSLT 3 msPOWER-GOOD OUTPUT (POK)POKUpperTripThresholdandOvervoltage-Fault Threshold Risingedge,50mVhysteresis 8.5 12 14 %

POKLowerTripThreshold Falling edge, 50mV hysteresis -14 -12 -6 %

POKLeakageCurrent IPOK TA = +25°C, VPOK = 5.5V 0.1 1 μA

POKPropagationDelayTime tPOK FBforced50mVbeyondPOKtripthreshold 2 μs

POKOutputLowVoltage ISINK = 3mA 100 mV

Overvoltage-FaultLatch-DelayTime

FBforced50mVabovePOKuppertripthreshold 2 μs

Undervoltage-FaultLatch-DelayTime

FBforced50mVbelowPOKlowertripthreshold, TUV 1.6 ms

LOGIC INPUTSENInputHighThreshold Rising,hysteresis=215mV(typ) 1.0 1.4 1.6 V

ENInputLeakageCurrent TA = +25°C 0.1 1 μATHERMAL SHUTDOWNThermal-Shutdown Threshold TSHDN Hysteresis = 15°C +160 °C



Electrical Characteristics (continued)

(VCC = 5V, VIN = 3.3V - 5V, VOUT=0.9V-3.3V,IOUT = 0–5A, TA = +25°C, unless otherwise noted.)

EFFICIENCYvs. OUTPUT CURRENT

MAX

1751

5 to

c01

OUTPUT CURRENT (mA)

EFFI

CIEN

CY (%

)

1k

65

70

75

80

85

90

95

100

60100 10k

VOUT = 0.9V

VIN = 3.3VVCC = 5.0V

VOUT = 1.2VVOUT = 1.8V

VOUT = 2.5V

EFFICIENCYvs. OUTPUT CURRENT

MAX

1751

5 to

c02

OUTPUT CURRENT (mA)

EFFI

CIEN

CY (%

)

1k

65

70

75

80

85

90

95

100

60100 10k

VOUT = 1.8V

VOUT = 3.3V

VOUT = 0.9VVOUT = 1.2V

VOUT = 2.5V

VIN = 5.0VVCC = 5.0V

LOAD REGULATION(VOUT = 0.75V)

MAX

1751

5 to

c03

OUTPUT CURRENT (A)

V OUT

(V)

4.54.00.5 1.0 1.5 2.5 3.02.0 3.5

0.740

0.745

0.750

0.755

0.760

0.765

0.770

0.775

0.7350 5.0

VOUT = 0.75VVCC = 5.0V

VIN = 5.0V

VIN = 3.3V


MAX

1751

5 to

c04

OUTPUT CURRENT (A)

V OUT

(V)

4.54.03.53.02.52.01.51.00.5

1.15

1.16

1.17

1.18

1.19

1.20

1.21

1.140 5.0


VIN = 5.0V

VIN = 3.3V


MAX

1751

5 to

c05

OUTPUT CURRENT (A)

V OUT

(V)

4.54.03.0 3.51.0 1.5 2.0 2.50.5

1.74

1.75

1.76

1.77

1.78

1.79

1.80

1.81

1.82

1.83

1.730 5.0


VIN = 5.0V

VIN = 3.3V


MAX

1751

5 to

c06

OUTPUT CURRENT (A)

V OUT

(V)

4.54.03.53.02.52.01.51.00.5

2.40

2.42

2.44

2.46

2.48

2.50

2.52

2.380 5.0


VIN = 5.0V

VIN = 3.3V

OUTPUT-VOLTAGE RIPPLE(VIN = 5V, VOUT = 1.2V, IOUT = 5A)

MAX17515 toc07

VOUT10mV/div(AC-COUPLED)

1µs/div

INPUT-VOLTAGE RIPPLE(VIN = 5V, VOUT = 1.2V, IOUT = 5A)

MAX17515 toc08

VIN50mV/div(AC-COUPLED)

1µs/div


Maxim Integrated 4www.maximintegrated.com

Typical Operating Characteristics


LOAD CURRENT TRANSIENT RESPONSE(VIN = 5.0V, VOUT = 1.2V, IOUT = 2.5 TO 5A)

MAX17515 toc10

IOUT

VOUT

2A/div

50mV/div(AC-COUPLED)

2ms/div


MAX17515 toc11

IOUT

VOUT

2A/div


2ms/div


MAX17515 toc12

IOUT

VOUT

2A/div


2ms/div

STARTUP WAVEFORM(VIN = 3.3V, VOUT = 1.2V, IOUT = 0A)

MAX17515 toc13

VLX

VEN

VOUT

VPOK

5V/div

5V/div

2V/div

500mV/div

400µs/div


MAX17515 toc09

IOUT

VOUT

2A/div


2ms/div

SHUTDOWN WAVEFORM(VIN = 3.3V, VOUT = 1.2V, IOUT = 30mA)

MAX17515 toc14

VLX

VEN

VOUT

VPOK

5V/div

5V/div

2V/div

500mV/div

400µs/div



Typical Operating Characteristics (continued)



MAX17515 toc15

VLX

VEN

VOUT

VPOK

5V/div

5V/div

2V/div

500mV/div

400µs/div

SHUTDOWN WAVEFORM(VIN = 3.3V, VOUT = 1.2V, IOUT = 5A)

MAX17515 toc16

VLX

VEN

VOUT

VPOK

5V/div

5V/div

2V/div

500mV/div

400µs/div


MAX17515 toc17

VLX

VEN

VOUT

VPOK

5V/div

5V/div

2V/div

500mV/div

400µs/div

SHUTDOWN WAVEFORM(VIN = 5.0V, VOUT = 1.2V, IOUT = 30mA)

MAX17515 toc18

VLX

VEN

VOUT

VPOK

5V/div

5V/div

2V/div

500mV/div

400µs/div


MAX17515 toc19

VLX

VEN

VOUT

VPOK

5V/div

5V/div

2V/div

500mV/div

400µs/div

SHUTDOWN WAVEFORM(VIN = 5.0V, VOUT = 1.2V, IOUT = 5A)

MAX17515 toc20

VLX

VEN

VOUT

VPOK

5V/div

5V/div

2V/div

500mV/div

400µs/div





LOAD SHORT-CIRCUIT(VIN = 5.0V, VOUT = 1.2V, IOUT = 0A)

MAX17515 toc21

IOUT

VOUT

VPOK

VLX

5A/div

5V/div

1V/div

2V/div

400µs/div

LOAD SHORT-CIRCUIT(VIN = 5.0V, VOUT = 1.2V, IOUT = 5A)

MAX17515 toc22

IOUT

VOUT

VPOK

VLX

5A/div

5V/div

1V/div

2V/div

400µs/div

MAX

1751

5 to

c23

AMBIENT TEMPERATURE (°C)

OUTP

UT C

URRE

NT (A

)

11010090807060

1

2

3

4

5

6

050 120

VOUT = 3.3V

VOUT = 1.8V

VOUT = 1.1V

OUTPUT CURRENTvs. AMBIENT TEMPERATURE

(VIN = 5.0V NO AIR FLOW)




5 6 7 8 9 10 11 12 13 14

POK

GND

GND

GND

VC

C

FB

EN

N.C

.

N.C

.

OU

T

OU

T

OUT

OUT

OUT

OUT

OU

T

OU

T

PGND

PGND

PGND

PGND

PGND

PGND

PGND

IN

19202122232425262728

415

IN

IN

IN

1

2

316

17

18MAX17515

EP 2EP 1

EP 3

PIN NAME FUNCTION

1–3, 28 IN

InputSupplyConnection.BypasstoGNDwitha22µFor2x10µFceramiccapacitor.Supplyrangeforthispin is 4.5V to 5.5V. When VCCcanbesuppliedseparatelyfroma4.5Vto5.5Vsource,theINpincanthenbepowered from a 2.4V to 5.5V supply.

4 POKOpen-DrainPower-GoodOutput.POKispulledlowifFBismorethan12%(typ)aboveorbelowthenominalregulationthreshold.POKisheldlowinshutdown.POKbecomeshighimpedancewhenFBisinregulationrange.Pullthispinupwith10kΩ(typ)resistorvalue.

5–7 GND GND.ConnectPGNDandGNDtogetheratasinglepoint.

8 VCC5VBiasSupplyInputfortheInternalSwitchingRegulatorDrivers.ForINfrom4.5Vto5.5V,VCC can be connectedtotheINsupply.ForINsupplyvoltageslowerthantheaboverange,VCC should be powered from aseparate5V±10%supplyandbypassedwitha1µForgreaterceramiccapacitor.

9 FBFeedbackInputfortheInternal5AStep-DownConverter.ConnectFBtoaresistivedividerbetweenOUTandGNDtoadjustthetypicaloutputvoltagebetween0.765Vto3.6V.Keepequivalentdividerresistancelowerthan50kΩ.

10 EN RegulatorEnableInput.WhenENispulledlow,theregulatorisdisabled.WhenENisdrivenhigh,theregulator is enabled.

11, 12 N.C. NoConnection

13–20 OUT RegulatorOutputPins.ConnectanoutputcapacitorbetweenOUTandPGNDwitha220µF(typ)POSCAPlow-ESRcapacitor.

21–27 PGND PowerGNDReturn.ConnecttoGND.— EP1 ExposedPad1.ConnectthispadtothePGNDandGNDgroundplanesof1inby1incopperforcooling.— EP2 ExposedPad2.DonotconnectthispadtoanyothernodeonthePCB.Minimizeareaofcopperisland.— EP3 Exposed Pad 3. Connect this pad to copper area of 1in by 1in. Electrically can be connected to the OUT pins.



Pin Description

Pin Configuration

VCC

EN

POK

GND

VREF

IN

+

-

VCC

BST

ZX

ILIM_VALLEY

OV COMP

0.1µF

PWMCONTROLLER

PWMCOMP

OSC

MAX17515

UVLO

POR

UVLO

2.2µF

OUT1µH

PGND

THERMAL FAULT+160°C

ILIM_PEAK

1.12 x VREF

+

-

+

-

+

-

+

-

+

-UV

COMP

0.88 x VREF+

-

FB

2.2µF

ISKIP



Functional Diagram

Design ProcedureAdjusting Output VoltageThe MAX17515 produces an adjustable 0.75V to 3.6Voutput voltage from a 2.4V to 5.5V input voltage range by usinga resistive feedbackdivider fromOUT toFB.Thedevice can deliver up to 5A output current up to an output voltage of 2.5V at +70°C. The output current derates for output voltages above 2.5V.Adjustingtheoutputvoltageofthedevicerequiresaresis-tive divider network from OUT to FB, according to theequation below. From the initial output voltage, the load-line regulation reduces the effective feedback voltage by a typical 5mV/A as the output current increases.

OUTU B

VR R 1

0.765 = × −

kΩ,whereRBisinkΩ.

Input Voltage RangeThe maximum value (VIN(MAX)) and minimum value (VIN(MIN)) must accommodate the worst-case conditions accounting for the input voltage soars and drops. If there is a choice at all, lower input voltages result in better efficiency.Withamaximumdutycycleof87.5%,VOUT is limited to 0.875 x VIN.

Input Capacitor SelectionThe input capacitor must meet the ripple-current require-ment (IRMS) imposed by the switching currents. The IRMS requirements of the regulator can be determined by the following equation:

RMS OUTI I D (1 D)= × × −

The worst-case RMS current requirement occurs whenoperatingwithD=0.5.Atthispoint,theaboveequationsimplifies to IRMS = 0.5 x IOUT.

The minimum input capacitor required can be calculated by the following equation:

( )( )IN_AVG

ININ SW

I (1 D)C

V f

× −=

∆ ×

where:IIN_AVGis the average input current given by:

OUTIN_Avg

IN

PI

V=η×

D is the operating duty cycle, which is approximatelyequal to VOUT/VINwhere: ∆VIN is the required input-voltage ripple, fSW is the operating switching frequency, POUT is the output power, which is equal to VOUT x

IOUT, ηistheefficiency.For the device’s system (IN) supply, ceramic capaci-tors are preferred due to their resilience to inrush surge currents typical of systems, and due to their low parasitic inductance, which helps reduce the high-frequency ring-ing on the IN supply when the internal MOSFETs areturned off. Choose an input capacitor that exhibits less than+10°CtemperatureriseattheRMSinputcurrentforoptimal circuit longevity.

Output Capacitor SelectionThe output capacitor selection requires careful evalua-tion of several different design requirements (e.g., stabil-ity, transient response, and output ripple voltage) that place limits on the output capacitance and the effective series resistance (ESR). Based on these requirements,acombinationoflow-ESRpolymercapacitors(lowercostbut higher output ripple voltage) and ceramic capacitors (higher cost but low output ripple voltage) should be used to achieve stability with low output ripple.

Loop CompensationThe gain portion of the loop gain is a result of error-amplifier gain, current-sensing gain, and load with an overall typical value at 1kHz of 36dB at VIN = 5V, and 46dBatVIN = 3V, with a typical limit to the gain-bandwidth (GBW)productof120,000.Thecrossovershouldoccurbefore this error-amplifier bandwidth limit of 120kHz (gain = 1). The output capacitor and load introduces a pole with the worst case at the maximum load (5A). If the load pole location is further than a frequency where Figure 1. Adjusting Output Voltage

OUT

MAX17515

VOUT

FB

RU

RB



thegainexceedstheGBW,thegaindropstartsearlieratthe location where the loop gain is limited. This situation applies typically to an output voltage less than 1.8V, so zero frequency from theESR isneeded to increase thephase margin at the crossover frequency. The recommended relationship between ESR and totaloutput capacitance values are shown in Table 1. When alow-ESRtypecapacitorisusedwithaceramiccapaci-tor, a recommended value of 44µF to 100µF ceramiccapacitor should be used to make up the total capaci-tancevaluewiththerelationshipbetweenESRandtotaloutput capacitance value, such that the zero frequency is between32kHzand40kHz.Whenonlya low-ESR typecapacitor is used, the zero frequency should be between 62kHz and 80kHz. Optionally, for an output greater than or equal to 1.8V, an all-ceramic capacitor solution can be used with a minimum capacitance value that locates the pole location below 1kHz with resistive load (5A), and with a simplified equation given by COUTMIN(µF)=900/VOUT.

Output Ripple VoltageWithpolymercapacitors, theESRdominatesanddeter-mines the output ripple voltage. The step-down regulator’s output ripple voltage (VRIPPLE) equals the total inductor ripple current (ΔIL) multiplied by the output capacitor’s ESR.Therefore, themaximumESR tomeet the outputripple-voltage requirement is:

RIPPLEESR

L

VRI

≤∆

where:IN OUT OUT

LIN SW

V V V 1IL V f

− ∆ = × ×

where fSWistheswitchingfrequencyandListheinduc-tor(1µH).

The actual capacitance value required relates to the physical case size needed to achieve theESR require-ment, as well as to the capacitor chemistry. Thus, polymer capacitorselectionisusuallylimitedbyESRandvoltagerating rather than by capacitance value. With ceramic capacitors, the ripple voltage due to capaci-tance dominates the output ripple voltage. Therefore, the minimum capacitance needed with ceramic output capacitors is:

OUTSW

LRIPPLE

I 1C8 f V ∆

= × ×

Alternatively,combiningceramics (for the lowESR)andpolymers (for the bulk capacitance) helps balance the out-put capacitance vs. output ripple-voltage requirements.

Load-Transient ResponseThe load-transient response depends on the overall out-put impedance over frequency, and the overall amplitude and slew rate of the load step. In applications with large, fast-loadtransients(loadstep>80%offullloadandslewrate > 10A/μs), the output capacitor’s high-frequencyresponse (ESL and ESR) needs to be considered. Toprevent the output voltage from spiking too low under a load-transientevent, theESR is limitedby the followingequation (ignoring the sag due to finite capacitance):

RIPPLESTEPESR

OUTSTEP

VR

I≤

∆

where VRIPPLESTEP is the allowed voltage drop during load current transient, and IOUTSTEP is the maximum load current step.The capacitance value dominates the mid-frequency output impedance and continues to dominate the load-transient response as long as the load transient’s slew rate is fewer than two switching cycles. Under these

Table 1. Output Capacitor Selection vs. ESR

TOTAL COUT (µF) LOW-ESR TYPE WITH CERAMIC-TYPE ESR (mΩ)

LOW-ESR TYPE WITHOUT CERAMIC-TYPE ESR (mΩ)

250 16–20 8–10300 13–17 7–9350 11–14 6, 7400 10–12 5, 6450 9–11 4–6500 8–10 4, 5550 7–9 4, 5600 7, 8 3, 4



Idle Mode is a trademark of Maxim Integrated Products, Inc

conditions, the sag and soar voltages depend on the output capacitance, inductance value, and delays in the transientresponse.Lowinductorvaluesallowtheinductorcurrent to slew faster, replenishing charge removed from or added to the output filter capacitors by a sudden load step, especially with low differential voltages across the inductor. The minimum capacitance needed to handle the sag voltage (VSAG) that occurs after applying the load current can be estimated by the following equation:

( ) ( )

OUT_SAGSAG

2STEP

STEP swMAX

1CV

L IOUT1 IOUT (t T)2 VIN D VOUT

= ×

× ∆ + ∆ × − ∆ × −

where: DMAXisthemaximumdutyfactor(87.5%), tSW is the switching period (1/fSW), ΔT equalsVOUT/VIN x tSW when in PWM mode, or

LxIIDLE/(VIN - VOUT) when in Idle Mode (1.5A). The minimum capacitance needed to handle the over-shoot voltage (VSOAR) that occurs after load removal (due to stored inductor energy) can be calculated as:

( )2STEPOUT

OUT SOAR

IOUT LC

2V V∆

≈

When the device is operating under low duty cycle, the output capacitor size is usually determined by the COUT_SOAR.

Detailed DescriptionThe MAX17515 is a complete step-down switch-mode power-supply solution that can deliver up to 5A output current and up to 3.6V output voltage from a 2.4V to 5.5V input voltage range. The device includes switch-mode power-supply controller, dual n-channel MOSFET power switches, and an inductor. The device uses a fixed-fre-quency current-mode control scheme.The device provides peak current-limit protection, output undervoltage protection, output overvoltage protection, and thermal protection. The device operates in skip mode at light loads to improve the light-load efficiency. Independent enable and an open-drain power-good out-put allow flexible system power sequencing. The fixed

voltage soft-start reduces the inrush current by gradually ramping up the internal reference voltage.

Fixed-Frequency Current-Mode Controller The heart of the current-mode PWM controller is a multistage, open-loop comparator that compares the output voltage-error signal with respect to the reference voltage, the current-sense signal, and the slope-compen-sation ramp (see the Functional Diagram). The device uses a direct summing configuration, approaching ideal cycle-to-cycle control over the output voltage without a traditional error amplifier and the phase shift associated with it.

Light-Load OperationThe device features an inherent automatic switchover to pulse skipping (PFM operation) at light loads. This switchover is affected by a comparator that truncates the low-side switch on-time at the inductor current’s zero crossing. The zero-crossing comparator senses the inductor current during the off-time. Once the current through the low-side MOSFET drops below the zero-crossing trip level, it turns off the low-side MOSFET. This prevents the inductor from discharging the output capaci-tors and forces the switching regulator to skip pulses under light-load conditions to avoid overcharging the output. Therefore, the controller regulates the valley of the output ripple under light-load conditions. The switching waveforms can appear noisy and asynchronous at light-load pulse-skipping operation, but this is a normal operat-ing condition that results in high light-load efficiency.

Idle Mode™ Current-Sense Threshold In Idle Mode, the on-time of the step-down controller ter-minates when both the output voltage exceeds the feed-back threshold, and the internal current-sense voltage falls below the Idle Mode current-sense threshold (IIDLE = 1.5A). Another on-time cannot be initiated until the output voltage drops below the feedback threshold. In this mode, the behavior appears like PWM operation with occasional pulse skipping, where inductor current does not need to reach the light-load level.

Power-On Reset (POR) and UVLOPower-on reset (POR) occurs when VCC rises above approximately 2.1V, resetting the undervoltage, over-voltage, and thermal-shutdown fault latches. The VCC inputundervoltage-lockout(UVLO)circuitryprevents theswitching regulators from operating if the 5V bias supply (VCC)isbelowits4VUVLOthreshold.



Soft-Start The internal step-down controller starts switching and the output voltage ramps up using soft-start. If the VCC biassupplyvoltagedropsbelowtheUVLOthreshold,thecontroller stops switching and disables the drivers (LXbecomes high impedance) until the bias supply voltage recovers.Once the 5V VCC bias supply and VIN rise above their respectiveinputUVLOthresholds,andENispulledhigh,the internal step-down controller becomes enabled and begins switching. The internal voltage soft-starts gradu-ally increment the feedback voltage by approximately 25mV every 61 switching cycles, making the output volt-agereachitsnominalregulationvoltage1.79msaftertheregulator is enabled (see the Soft-Start Waveforms in the Typical Operating Characteristics section).

Power-Good Output (POK) POKis theopen-drainoutputof thewindowcomparatorthat continuously monitors the output for undervoltage and overvoltage conditions. POK is actively held low inshutdown (EN=GND). POKbecomes high impedanceafter the device is enabled and the output remains within ±10%of thenominal regulationvoltagesetbyFB.POKgoeslowoncetheoutputdrops12%(typ)beloworrises12%(typ)aboveitsnominalregulationpoint,ortheoutputshuts down. For a logic-level POK output voltage, con-nectanexternalpullupresistorbetweenPOKandVCC. A 10kΩpullupresistorworkswellinmostapplications.

Output Overvoltage Protection (OVP) If the output voltage rises to 112% (typ) of its nominalregulation voltage, the controller sets the fault latch, pulls POK low, shuts down the regulator, and immediatelypulls the output to ground through its low-side MOSFET. Turningon the low-sideMOSFETwith100%dutycyclerapidly discharges the output capacitors and clamps the output to ground. However, this commonly undamped response causes negative output voltages due to the energystoredintheoutputLCattheinstantof0Vfault.Ifthe load cannot tolerate a negative voltage, place a power Schottky diode across the output to act as a reverse-polarity clamp. If the condition that caused the overvolt-age persists (such as a shorted high-side MOSFET), the input source also fails (short-circuit fault). Cycle VCC

below 1V or toggle the enable input to clear the fault latch and restart the regulator.

Output Undervoltage Protection (UVP) The device includes an output undervoltage-protection (UVP) circuit that begins to monitor the output once the startup blanking period has ended. If the output voltage dropsbelow88%(typ)of itsnominal regulationvoltage,the regulator pulls the POK output low and begins theUVP fault timer. Once the timer expires after 1.6ms, the regulator shuts down, forcing the high-side MOSFET off and disabling the low-side MOSFET once the zero-crossing threshold has been reached. Cycle VCC below 1V, or toggle the enable input to clear the fault latch and restart the regulator.

Thermal-Fault Protection The device features a thermal-fault protection circuit. Whenthejunctiontemperaturerisesabove+160°C(typ),a thermal sensor activates the fault latch, pulls down the POKoutput,andshutsdowntheregulator.ToggleENtoclear the fault latch, and restart the controllers after the junctiontemperaturecoolsby15°C(typ).

Power DissipationThe device output current needs to be derated if the out-put voltage is above 2.5V or if the device needs to oper-ate in high ambient temperature. The amount of current derating depends upon the input voltage, output voltage, and ambient temperature. The derating curves given in the Typical Operating Characteristics section can be used as a guide.The maximum allowable power losses can be calculated using the following equation:

JMAX AMAX

JA

T TPD

−=

q

where: PDMAX is the maximum allowed power losses with

maximumallowedjunctiontemperature, TJMAXisthemaximumallowedjunctiontemperature, TA is operating ambient temperature, qJAisthejunction-to-ambientthermalresistance.



PCB Layout GuidelinesCarefulPCB layout iscritical toachieving lowswitchinglosses and clean, stable operation. Use the following guidelinesforgoodPCBlayout: Keeptheinputcapacitorsascloseaspossibletothe

INandPGNDpins. Keeptheoutputcapacitorsascloseaspossibletothe

OUTandPGNDpins. ConnectallthePGNDconnectionstoaslargeacop-

per plane area as possible on the top layer. ConnectEP1tothePGNDandGNDplanesonthetop

layer. UsemultipleviastoconnectinternalPGNDplanesto

thetop-layerPGNDplane. DonotkeepanysoldermaskonEP1–EP3onbottom

layer.Keepingsoldermaskonexposedpadsdecreas-es the heat-dissipating capability.

Keep the power traces and load connections short.This practice is essential for high efficiency. Using thickcopperPCBs(2ozvs.1oz)canenhancefull-loadefficiency. Correctly routing PCB traces is a difficulttask that must be approached in terms of fractions of centimeters, where a single milliohm of excess trace resistance causes a measurable efficiency penalty. Figure 2. Layout Recommendation

+Denotes a lead(Pb)-free/RoHS-compliant package.

5 6 7 8 9 10 11 12 13 14

19202122232425262728

4 15

1

2

3 16

17

18EP 2EP 1 EP 3

GND

PGND

VIN

VOUT

VOUTPGND

PART TEMP RANGE PIN-PACKAGEMAX17515ELI+ -40°C to +85°C 28 SIP

PACKAGE TYPE

PACKAGE CODE

OUTLINE NO.

LAND PATTERN NO.

28 SIP L286510+1 21-0701 90-0445



Package InformationFor the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages.Notethata“+”,“#”,or“-”inthepackagecodeindicatesRoHSstatusonly. Package drawings may show a different suffix character, but thedrawingpertainstothepackageregardlessofRoHSstatus.

Chip InformationPROCESS:BiCMOS

Ordering Information

http://pdfserv.maximintegrated.com/package_dwgs/21-0701.PDF

http://pdfserv.maximintegrated.com/land_patterns/90-0445.PDF

REVISIONNUMBER

REVISIONDATE DESCRIPTION PAGES

CHANGED0 6/13 Initial release —

Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.

Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.


© 2013 Maxim Integrated Products, Inc. 15

Revision History

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

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