MP38894 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER

MP38894 Rev.1.0

www.MonolithicPower.com

9

9/28/2009

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PCB Layout Guide

PCB layout is very important to achieve stable

operation. Please follow these guidelines and

take Figure3 for references.

1) Keep the path of switching current short

and minimize the loop area formed by Input

cap, high-side and low-side MOSFETs.

2) Keep the connection of low-side MOSFET

between SW pin and input power ground

as short and wide as possible.

3) Ensure all feedback connections are short

and direct. Place the feedback resistors

and compensation components as close to

the chip as possible.

4) Route SW away from sensitive analog

areas such as FB.

5) Connect IN, SW, and especially GND

respectively to a large copper area to cool

the chip to improve thermal performance

and long-term reliability.

Top Layer

Bottom Layer

Figure 3—PCB Layout

External Bootstrap Diode

An external bootstrap diode may enhance the

efficiency of the regulator, the applicable

conditions of external BST diode are:

Duty cycle is high: D=

IN

OUT

V

V

>65%

In these cases, an external BST diode is

recommended from the output of the voltage

regulator to BST pin, as shown in Fig.4

MP38894

SW

BST

C

L

BST

5V or 3.3V

External BST Diode

IN4148

Figure 4—Add Optional External Bootstrap

Diode to Enhance Efficiency

The recommended external BST diode is

IN4148, and the BST cap is 0.1~1µF.