AP6508

500kHz 21V 3A SYNCHRONOUS DC/DC BUCK CONVERTER

AP6508

Document number: DS33437 Rev. 4 - 2

2 of 14

www.diodes.com

July 2011

© Diodes Incorporated

Pin Descriptions

Pin #

Name

Description

1

IN

Supply Voltage. The AP6508 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.

2,3,4,5

SW

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

6

BST

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

supply across the high-side switch driver.

7

EN

EN=1 to enable the chip. For automatic start-up, connect EN pin to VIN by proper EN resistor

divider as Figure 1 shows.

8

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.

9

PG

Power Good

10

SS

External Softstart

11

BIAS Supply. Decouple with 0.

μ1F – 0.22μF cap. And the capacitance should be no more

than 0.22

μF

12, 13

GND

System Ground. This pin is the reference ground for the regulated output voltage. For this

reason care must be taken in its PCB layout. Suggested to be connected to GND with copper

and vias.

14

AGND

Analog Ground

Exposed PAD

No internal connection. It is recommended to connect exposed pad to GND plane for optimal

thermal performance

Functional Block Diagram