AMS4123

3A 20V Step-Down Converter + 1A LDO

3/5/2010

www.advanced-monolithic.com

Phone (925) 443-0722

2

Fax (925) 443-0723

Pin Description

Pin #

Symbol

Description

1

SW

Step-Down converter switching node that connects the internal power switch to the

output inductor.

2

BST

The bootstrap capacitor tied to this pin is used as the bias source for the drive to the

internal power switch. Use a 220nF or greater capacitor from the BST to the SW

pin.

3

Vin

Input Power. Supplies bias to the IC and is also the power input to the step-down

converter main power switch. Bypass Vin with low impedance ceramic with

sufficient capacitance to minimize switching frequency ripple as well as high

frequency noise.

4

EN

Enable. A voltage greater than 2V at this pin enables the switching regulator. 2.5V

enables the LDO section.

5

FB SW

Step-Down Converter Feedback input. A resistor network of two resistors is used to

the two resistors is connected to Feedback Switch pin.

6

FB LDO

LDO Feedback input. A resistive voltage divider is used to set the output voltage

connected between the LDO output and GND. The node between the two resistors

is connected to FB LDO pin.

7

LDO in

LDO Input. Connect to the output of the Step-Down converter. LDO IN can also be

powered from any power supply as long as it is 2V less than Vin.

8

LDO out

LDO Output pin.

9

GND (PADDLE)

Ground paddle to be connected to PCB ground plane. This is also the ground for

internal voltage reference.

Pin Configuration

8L SOIC

SO Package (S)

Top View