AAT1147IJS-0.6-T1 データシートの表示（PDF） - Analog Technology Inc

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AAT1147IJS-0.6-T1

High Efficiency, Low Noise, Fast Transient 400mA Step-Down Converter

Analog Technology Inc 

AAT1147

High Efficiency, Low Noise, Fast Transient

400mA Step-Down Converter

1

2

3

Enable

VIN

C4

100pF

VOUT =1.8V

R1

L1 118k

4.7μH

C1

10μF

C3

n/a

R2

59k

U1

AAT1147

1

8

EN PGND

2

7

OUT PGND

3

6

VIN PGND

4

5

LX AGND

C2

4.7μF

GND

GND2

LX

U1 AAT1147 SC70JW-8

L1 CDRH3D16-4R7

C2 4.7μF 10V 0805 X5R

C1 10μF 6.3V 0805 X5R

Figure 1: Enhanced Transient Response Schematic.

Control Loop

The AAT1147 is a peak current mode step-down

converter. The current through the P-channel

MOSFET (high side) is sensed for current loop

control, as well as short circuit and overload pro-

tection. A fixed slope compensation signal is added

to the sensed current to maintain stability for duty

cycles greater than 50%. The peak current mode

loop appears as a voltage-programmed current

source in parallel with the output capacitor.

The output of the voltage error amplifier programs

the current mode loop for the necessary peak

switch current to force a constant output voltage for

all load and line conditions. Internal loop compen-

sation terminates the transconductance voltage

error amplifier output. The error amplifier reference

is 0.6V.

Soft Start / Enable

Soft start limits the current surge seen at the input

and eliminates output voltage overshoot. When

pulled low, the enable input forces the AAT1147

into a low-power, non-switching state. The total

input current during shutdown is less than 1µA.

Current Limit and Over-Temperature

Protection

For overload conditions, the peak input current is

limited. To minimize power dissipation and stresses

under current limit and short-circuit conditions,

switching is terminated after entering current limit

for a series of pulses. Switching is terminated for

seven consecutive clock cycles after a current limit

has been sensed for a series of four consecutive

clock cycles.

Thermal protection completely disables switching

when internal dissipation becomes excessive. The

junction over-temperature threshold is 140°C with

15°C of hysteresis. Once an over-temperature or

over-current fault conditions is removed, the output

voltage automatically recovers.

Under-Voltage Lockout

Internal bias of all circuits is controlled via the VIN

input. Under-voltage lockout (UVLO) guarantees

sufficient VIN bias and proper operation of all inter-

nal circuitry prior to activation.

1147.2006.05.1.0

9

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