Output Capacitor Selection

The X7R ceramic output capacitors are preferred due to

their stability over temperature in industrial applications.

The minimum recommended output capacitor values

in Table 1 are for desired output voltages to support

a dynamic step load of 50% of the maximum output

current in the application. For additional adjustable output

voltages, the output capacitance value is derived from the

following equation:

STEP

RESPONSE

OUT

OUT

It

C

2V

×

=

×∆

C

0.33

RESPONSE

f

SW

1

t

f

≈+

greater than 500kHz.

Loop Compensation

The MAXM17543 integrates the internal compensation

to stabilize the control loop. Only the device requires

a combination of output capacitors and feedback

resistors to program the closed-loop crossover frequency

component values to compensate with appropriating

operating switching frequency. Connect a capacitor from

CF to FB to correct frequency response in applica-

tions using non-ceramic output capacitors with switching

frequency below 500kHz. Place a 2.2pF for switching

frequency below 300kHz, and 1.2pF for switching

frequency range of 300kHz to 400kHz.

Setting the Switching Frequency (RT)

The switching frequency range of 100kHz to 1.8MHz are

recommended from Table 1 for desired input and output

voltages. The switching frequency of MAXM17543 can be

is given by the following equation:

RT

SW

21000

R

1.7

f

≈−

pin open to operate at the default switching frequency of

500kHz.

Soft-Start Capacitor Selection

The device implements an adjustable soft-start opera-

tion to reduce inrush current during startup. A capacitor

3

SS

SEL

OUT

C

28 10

C

V

−

≥×

×

×

The value of the soft-start capacitor is calculated from the

desired soft-start time as follows:

SS

t

5.55

≈

Detailed Description

The MAXM17543 is a complete step-down DC-DC power

supply that delivers up to 2.5A output current. The device

provides a programmable output voltage to regulate up

to 12V through external resistor dividers from an input

voltage range of 4.5V to 42V. The recommended input

voltage in Table 1 is selected highly enough to support

the desired output voltage and load current. The device

includes an adjustable frequency feature range from

100kHz to 1.8MHz to reduce sizes of input and output

capacitors. The Functional Diagram shows a complete

internal block diagram of the MAXM17543 power module.

Input Undervoltage-Lockout Level

The MAXM17543 contains an internal pullup resistor

(3.3MΩ) from EN to IN to have a default startup voltage.

The device offers an adjustable input undervoltage-

lockout level to set the voltage at which the device is

turned on by a single resistor connecting from EN/UVLO

to SGND as equation:

ENU

INU

3.3 1215

R

(V

1.215)

×

≈

−

the device is required to turn on the device. Ensure that

minimum input voltage for each desired output voltage.

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Maxim Integrated │ 14

MAXM17543

4.5V to 42V, 2.5A High-Efficiency, DC-DC Step-Down

Power Module with Integrated Inductor