AAT1152 データシートの表示（PDF） - Advanced Analogic Technologies

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AAT1152

850kHz 1A Buck DC/DC Converter

Advanced Analogic Technologies 

Functional Block Diagram

AAT1152

850kHz 1A Buck DC/DC Converter

VCC

VP = 2.7V to 5.5V

1.0V REF

FB

OP. AMP

CMP

DH

LOGIC

LX

OSC

DL

Temp.

Sensing

Power

Good

SGND POK

EN

PGND

Applications Information

Control Loop

The AAT1152 is a peak current mode buck convert-

er. The inner wide bandwidth loop controls the peak

current of the output inductor. The output inductor

current is sensed through the P-channel MOSFET

(high side) and is also used for short-circuit and

overload protection. A fixed slope compensation sig-

nal is added to the sensed current to maintain sta-

bility. The loop appears as a voltage-programmed

current source in parallel with the output capacitor.

The voltage error amplifier output programs the cur-

rent loop for the necessary inductor current to force

a constant output voltage for all load and line con-

ditions. The feedback resistive divider is internal,

dividing the output voltage to the error amplifier ref-

erence voltage of 1V. The error amplifier does not

have the large DC gain typical of most error ampli-

fiers. This eliminates the need for external compen-

sation components, while still providing sufficient

DC loop gain for load regulation. The crossover fre-

quency and phase margin are set by the output

capacitor value only.

Soft Start/Enable

Soft start increases the inductor current limit point in

discrete steps when the input voltage or enable

input is applied. It limits the current surge seen at

the input and eliminates output voltage overshoot

(see Figure 1). When pulled low, the enable input

forces the AAT1152 into a low-power, non-switching

state. The total input current during shutdown is

less than 1μA.

1152.2006.09.1.7

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