MP8709 – SYNCHRONOUS STEP-DOWN CONVERTER WITH INTERNAL MOSFETS

MP8709 Rev. 1.01

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4

12/14/2011

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PIN FUNCTIONS

Pin #

Name

Description

1

IN

Supply Voltage. The MP8709 operates from a +4.5V to +21V input rail. C1 is

needed to decouple the input rail. Use wide PCB trace to make the connection.

2,3

SW

Switch Output. Use wide PCB trace to make the connection.

4

BST

Bootstrap. A capacitor connected between SW and BS pins is required to form a

floating supply across the high-side switch driver.

5

EN/SYNC

EN=1 to enable the chip. External clock can be applied to EN pin for changing

switching frequency. For automatic start-up, connect EN pin to VIN by proper EN

resistor divider as Figure 2 shows.

6

FB

Feedback. An external resistor divider from the output to GND, tapped to the FB

pin, sets the output voltage. To prevent current limit run away during a short

circuit fault condition the frequency fold-back comparator lowers the oscillator

frequency when the FB voltage is below 500mV.

7

VCC

8

GND,

Exposed Pad

System Ground. This pin is the reference ground of the regulated output voltage.

For this reason care must be taken in PCB layout. Suggested to be connected to

GND with copper and vias.