Design Procedure

Setting the Output Voltage

The MAXM17543 supports an adjustable output

voltage range of 0.9V to 12V from an input voltage range

of 4.5V to 42V by using a resistive feedback divider from

OUT to FB. Table 1 provides the feedback dividers for

desired input and output voltages. Other adjustable output

voltages can be calculated by following the procedure to

choose the resistive voltage-divider values:

U

C

OUT

216 1000

R

fC

×

=

×

frequency is less than or equal to 500kHz. If the switching

U

BB

OUT

R

0.9

R

k , whereR isink .

V

0.9

×

=

ΩΩ

−

Input Voltage Range

Due to the limitation of minimum and maximum duty

conditions, accounting for the input voltage rises and

drops. To simplify, Table 1 provides operating input

voltage ranges of different desired output voltages.

Input Capacitor Selection

The input capacitor serves to reduce the current peaks

drawn from the input power supply and reduces switching

noise to the IC. The input capacitor values in Table 1 are

the minimum recommended values for desired input and

output voltages. Applying capacitor values larger than

those indicated in Table 1 are acceptable to improve the

dynamic response. For further operating conditions, the

total input capacitance must be greater than or equal to

the value given by the following equation in order to keep

the input-voltage ripple within specifications and minimize

the high-frequency ripple current being fed back to the

input source:

IN_AVG

IN

IN

I

(1 D)

C

V

f

× −

=

∆

SW

×

where:

OUT

IN_AVG

IN

P

I

V

=

η×

D is the operating duty cycle, which is approximately

η is the efficiency.

The input capacitor must meet the ripple-current require-

ment imposed by the switching currents. The RMS input

ripple current is given by:

RMS

OUT

I

I

D (1 D)

=

×

× −

The worst-case RMS current requirement occurs when

operating with D = 0.5. At this point, the above equation

For the MAXM17543 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 that helps reduce the high-frequency ring-

ing on the IN supply when the internal MOSFETs are

turned off. Choose an input capacitor that exhibits less

than +10°C temperature rise at the RMS input current for

optimal circuit longevity.

Figure 1. Adjustable Output Voltage

OUT

FB

MAXM17543

www.maximintegrated.com

Maxim Integrated │ 12

MAXM17543

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

Power Module with Integrated Inductor