MAX17536ATP datasheet(15/19 Pages) MAXIM

15 / 19 page

Select a low-loss inductor closest to the calculated

value with acceptable dimensions and having the lowest

possible DC resistance. The saturation current rating

(ISAT) of the inductor must be high enough to ensure that

saturation can occur only above the peak current-limit

value.

Output Capacitor Selection

X7Rceramicoutputcapacitorsarepreferredduetotheir

stability over temperature in industrial applications. The

outputcapacitorsareusuallysizedtosupportastepload

of 50% of the maximum output current in the application,

so the output-voltage deviation is contained to 3% of the

output-voltage change. The minimum required output

capacitance can be calculated as follows:

= ×

∆

STEP

RESPONSE

OUT

≅+

RESPONSE

0.33

()

where ISTEP is the load current step, tRESPONSE is the

response time of the controller, DVOUT is the allowable

output-voltage deviation, fC is the target closed-loop

crossover frequency, and fSW is the switching frequency.

Select fC to be 1/9th of fSW if the switching frequency is

lessthanorequalto450kHz.Iftheswitchingfrequencyis

greaterthan450kHz,selectfCtobe50kHz.

Soft-Start Capacitor Selection

The MAX17536 implements adjustable soft-start operation

to reduce inrush current. A capacitor connected from

the SS pin to SGND programs the soft-start time. The

selected output capacitance (CSEL) and the output

voltage (VOUT) determine the minimum required soft-start

capacitor as follows:

CSS≥28x10-6 x CSEL x VOUT

The soft-start time (tSS) is related to the capacitor

connected at SS (CSS) by the following equation:

tSS = CSS/(5.55 x 10-6)

For example, to program a 4ms soft-start time, a 22nF

capacitorshouldbeconnectedfromtheSSpintoSGND.

Setting the Input Undervoltage-Lockout Level

The MAX17536 offers an adjustable input undervoltage-

lockout level. Set the voltage at which the device turns

on with a resistive voltage-divider connected from VIN to

SGND (See Figure 1). Connect the center node of the

dividertoEN/UVLO.

ChooseR1tobe3.3MIandthencalculateR2asfollows:

INU

R1 1.215

-1.215)

where VINU is the voltage at which the device is required

to turn on. Ensure that VINU is higher than 0.8 x VOUT.

Loop Compensation

TheMAX17536isinternallyloopcompensated.However,

iftheswitchingfrequencyislessthan450kHz,connecta

0402 capacitor (C12) between the CF pin and the FB pin.

Use Table 2 to select the value of C12.

Adjusting Output Voltage

Set the output voltage with a resistive voltage-divider

connected from the positive terminal of the output

capacitor (COUT)toSGND(seeFigure 2). Connect the

center node of the divider to the FB pin. Use the following

procedure to choose the resistive voltage-divider values:

CalculateresistorR3fromtheoutputtoFBasfollows:

OUT_SEL

451 10

whereR3isinkI,crossoverfrequencyfCisinkHz,and

COUT_SEL is Actual derated capacitance of selected

outputcapacitoratDC-biasvoltageinμF.ChoosefC to

be 1/9th of the switching frequency (fSW) if the switching

frequencyislessthanorequalto450kHz.Iftheswitching

frequencyisgreaterthan450kHz,selectfCtobe50kHz.

CalculateresistorR4fromFBtoSGNDasfollows:

OUT

R3 0.9

- 0.9)

Figure 1. Setting the Input Undervoltage Lockout

SGND

EN/UVLO

VIN

Maxim Integrated │ 15

MAX17536

4.5V to 60V, 4A, High-Efficiency, Synchronous

Step-Down DC-DC Converter

with Internal Compensation

MAX17536ATP Datasheet(PDF) 15 Page - Maxim Integrated Products

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