MPM3530

– 55V, 3A, STEP-DOWN POWER MODULE

MPM3530 Rev. 1.0

www.MonolithicPower.com

16

9/21/2018

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3. C3 can be calculated with Equation (19):

C

f

R3

2

π

4

C3







(19)

Determine if C4 is required. C4 is required if

the ESR zero of the output capacitor is

valid:

2

f

R

C2

2

π

1

SW

ESR







(20)

If this is the case, use C4 to set the pole

Determine C4 with Equation (21):

R3

R

C2

C4

ESR





(21)

External Bootstrap Diode

65%, there is less time available for the

bootstrap charging, so the bootstrap capacitor

may not be charged sufficiently. This affects

efficiency and normal operation. An external

bootstrap diode from the 3 - 5V rail to BST can

help

charge

the

bootstrap

capacitor

and

enhance efficiency (see Figure 2). The output

voltage is a good choice for this power supply if

it is in the above range. The bootstrap diode

can be a low-cost one, such as IN4148 or

BAT54.

L

BST

SW

3V-5V Rail

1N4148

Figure 2: External Bootstrap Diode

At no load or light load, the converter may

operate in pulse-skip mode to maintain the

output-voltage regulation. Under this condition,

capacitor. For a sufficient gate voltage during

must exceed 3.3V + 3V = 6.3V to maintain a

sufficient bootstrap voltage at no load or light

load. To meet this requirement,

EN can

Efficient

PCB

layout

is

critical for

stable

operation. For best results, refer to Figure 3 and

follow the guidelines below.

1. Keep the connection of the input ground

and GND as short and wide as possible.

2. Ensure that all feedback connections are

short and direct.

3. Place the feedback resistors as close as to

the chip as possible.

4. Route sensitive analog areas such as FB

away from SW.

5. Place enough vias around the chip for better

thermal performances.