MP28257 –4A, 4.2V-TO-20V, FAST TRANSIENT, SYNCHRONOUS STEP-DOWN CONVERTER

MP28257 Rev 1.0

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4

11/8/2011

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PIN FUNCTIONS

QFN12

(2x3mm)

Pin #

Name

Description

9

IN

Supply Voltage. The MP28257 operates from a 4.2V to 20V input rail. C1 decouples

the input rail. Use wide PCB traces and multiple vias to make the connection.

1, 11, 12

GND

System Ground. Reference ground for the regulated output voltage. These pins

require special consideration during PCB layout.

2, 10,

Exposed Pad

SW

Switch Output. Connect with wide PCB traces.

3

BST

Bootstrap. Requires a capacitor connected between SW and BST pins to form a

floating supply across the high-side switch driver.

4

VCC

Internal Bias Supply. Decouple with a 1µF ceramic capacitor as close to the pin as

possible.

5

EN

EN = 1 to enable the MP28257. For automatic start-up, connect EN pin to VIN with a

pull-up resistor.

7

FB

Feedback. Sets the output voltage when connected to the tap of an external resistor

divider, connected between output and GND.

8

FREQ

Frequency. Set during CCM operation. Connect a resistor R7 to IN to set the switching

frequency. Decouple with a 1nF capacitor.

6

PG

Power-Good Output. The output of this pin is an open drain that goes high if the output

voltage is higher than 90% of the nominal voltage. There is a 0.5ms delay between

when the feedback exceeds 90% to when the PG pin goes high.