AAT1153

2A Step-Down Converter

PRODUCT DATASHEET

1153.2008.02.1.2

9

www .analogictech.com

Functional Description

The AAT1153 is a high output current monolithic switch-

mode step-down DC-DC converter. The device operates

at a fixed 1.2MHz switching frequency, and uses a slope

compensated current mode architecture. This step-down

DC-DC converter can supply up to 2A output current at

5.5V. It minimizes external component size and opti-

mizes efficiency at the heavy load range. The slope com-

pensation allows the device to remain stable over a

wider range of inductor values so that smaller values

(1μH to 4.7μH) with lower DCR can be used to achieve

higher efficiency. Apart from the small bypass input

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

The fixed output version requires only three external

sion can be programmed with external feedback to any

voltage, ranging from 0.6V to near the input voltage. It

uses internal MOSFETs to achieve high efficiency and can

generate very low output voltages by using an internal

reference of 0.6V. At dropout, the converter duty cycle

increases to 100% and the output voltage tracks the

high-side MOSFET and the inductor DCR. The internal

error amplifier and compensation provides excellent

transient response, load and line regulation. Internal soft

start eliminates any output voltage overshoot when the

enable or the input voltage is applied.

Current Mode PWM Control

Slope compensated current mode PWM control provides

stable switching and cycle-by-cycle current limit for

excellent load and line response with protection of the

internal main switch (P-channel MOSFET) and synchro-

nous rectifier (N-channel MOSFET). During normal

operation, the internal P-channel MOSFET is turned on

for a specified time to ramp the inductor current at each

rising edge of the internal oscillator, and switched off

when the peak inductor current is above the error volt-

age.

inductor current. When the main switch is off, the syn-

chronous rectifier turns on immediately and stays on

until either the inductor current starts to reverse, as

the beginning of the next clock cycle.

Functional Block Diagram

R1*

R2*

R1*

R2*

PWM

LOGIC

IN

V

V

OUT

C

OUT

LX

L1

PGND

OVDET

OSC

SLOPE

COMP

Softstart

REF

0.65V

0.6V

0.6V

AIN AGND

I

COMP

SET

RESET

SHUTDOWN

EN

FB/OUT

Over-Temperature

and Short-Circuit

Protection

*The resistor divider R1 + R2 is internally set for the fixed output versions, and is externally set for the adjustable output versions.

NON-OVERLAP

CONTROL

COMP

I

SENSE

AMP