Functional Block Diagram

EN

LX

Err

.

Amp

Logic

DH

DL

PGND

VIN

OUT

AGND

Voltage

Reference

INPUT

See note

Note: For adjustable version, the internal feedback divider is omitted and the FB pin is tied directly

to the internal error amplifier.

AAT1143

1MHz 400mA Step-Down Converter

8

1143.2006.07.1.10

Functional Description

The AAT1143 is a high performance 400mA 1MHz

monolithic step-down converter. It has been

designed with the goal of minimizing external com-

ponent size and optimizing efficiency over the com-

plete load range. Apart from the small bypass input

capacitor, only a small L-C filter is required at the

output. Typically, a 4.7μH inductor and a 4.7μF

ceramic capacitor are recommended (see table of

values).

The fixed output version requires only three external

adjustable version can be programmed with external

feedback to any voltage, ranging from 0.6V to the

input voltage. An additional feed-forward capacitor

can also be added to the external feedback to pro-

vide improved transient response (see Figure 1).

At dropout, the converter duty cycle increases to

100% and the output voltage tracks the input volt-

side MOSFET.

The input voltage range is 2.7V to 5.5V. The con-

verter efficiency has been optimized for all load

conditions, ranging from no load to 400mA.

The internal error amplifier and compensation pro-

vides excellent transient response, load, and line

regulation. Soft start eliminates any output voltage

overshoot when the enable or the input voltage is

applied.