MPM3686 – 18V 20A STEP-DOWN POWER MODULE

MPM3686 Rev. 1.02

www.MonolithicPower.com

17

10/13/2016

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For simplification, choose an input capacitor with

an RMS current rating that exceeds half the

maximum load current.

The input capacitance value determines the

converter input voltage ripple. Select a capacitor

value that meets any input voltage ripple

requirements.

Estimate the input voltage ripple as follows:

)

V

V

1

(

V

V

C

F

I

V

IN

OUT

IN

OUT

IN

SW

OUT

IN













(18)

where:

IN

SW

OUT

IN

C

F

I

4

1

V









(19)

PCB Layout Recommendations

1. Place the input/output capacitors on the same

side of the MPM3686, and as close to the

MPM3686 package as possible.

2. A solid system ground layer is required to be

placed immediately below the surface layer with

the MPM3686.

3. Thermal VIAs (18 mil diameter and 8 mil hole

size) are required to be placed underneath the

GND, IN and VOUT pads, as well as the edges

of the MPM3686 and the input/output capacitors.

4. Keep the DC_trim traces as short as possible.

Figure 10

CIN1

CIN2

COUT1

COUT2

SW

Rtrim

Ctrim

IN

VOUT

GND

COUT3

CIN3

PG

VCC

AGND

SS

AGND

EN

>FERQ

VIN

DC_trim>

FREQ>

AGND

N/C

BST

VOUT

SW

SW

SW

SW

N/C

VOUT

VOUT

VOUT

VOUT

VOUT

VOUT

SW