MP38875 – 15A, 16V, 800kHz STEP-DOWN WITH SYNCHRONOUS GATE DRIVER

MP38875 Rev. 0.9

www.MonolithicPower.com

12

11/20/2009

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Bottom Layer

Figure 4—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 Figure.5

MP38875

SW

BST

C

L

BST

C

5V or 3.3V

OUT

External BST Diode

IN4148

+

Figure 5—Add Optional External Bootstrap

Diode to Enhance Efficiency

The recommended external BST diode is

IN4148, and the BST cap is 0.1~1µF.

Output Voltage Tracking and Sequencing

The MP38875 allows the user to program how

its output voltage ramps during startup by

means of the SS pin. Through this pin, the

output

voltage

can

be

set

to

either

coincidentally or rationally track another output

voltage, as shown below.

MP38875

FB

SW

SS

MP38875

FB

SW

SS

(a) Coincidentally Tracking

(a) Rationally Tracking

MP38875

FB

SW

SS

MP38875

FB

SW

SS

Figure 6—Output Voltage Tracking