AAT1147IJS-0.6-T1 View Datasheet(PDF) - Analog Technology Inc

Part Name

Description

MFG CO.

AAT1147IJS-0.6-T1

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

Analog Technology Inc 

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AAT1147

High Efficiency, Low Noise, Fast Transient

400mA Step-Down Converter

The AAT1147, combined with an external feedfor-

ward capacitor (C4 in Figure 1), delivers enhanced

transient response for extreme pulsed load appli-

cations. The addition of the feedforward capacitor

typically requires a larger output capacitor C1 for

stability.

VOUT (V)

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.8

1.85

2.0

2.5

3.3

R2 = 59kΩ

R1 (kΩ)

19.6

29.4

39.2

49.9

59.0

68.1

78.7

88.7

118

124

137

187

267

R2 = 221kΩ

R1 (kΩ)

75

113

150

187

221

261

301

332

442

464

523

715

1000

Table 2: Resistor Values For Use With 0.6V

Step-Down Converter.

Thermal Calculations

There are three types of losses associated with the

AAT1147 step-down converter: switching losses,

conduction losses, and quiescent current losses.

Conduction losses are associated with the RDS(ON)

characteristics of the power output switching

devices. Switching losses are dominated by the

gate charge of the power output switching devices.

At full load, assuming continuous conduction mode

(CCM), a simplified form of the losses is given by:

PTOTAL

=

IO2

·

(RDSON(H)

·

VO

+ RDSON(L)

VIN

·

[VIN

-

VO])

+ (tsw · FS · IO + IQ) · VIN

IQ is the step-down converter quiescent current.

The term tsw is used to estimate the full load step-

down converter switching losses.

VIN

VOUT

C1

10μF

GND

1

2

3

Enable

R1

118k

L1

4.7μH

R2

59k

U1

AAT1147

1 EN PGND 8

2 OUT PGND 7

3 VIN PGND 6

4 LX AGND 5

C2

4.7μF

GND2

LX

U1 AAT1147 SC70JW-8

L1 CDRH3D16-4R7

C1 10μF 10V 0805 X5R

C2 4.7μF 10V 0805 X5R

Figure 5: AAT1147 Evaluation Board Schematic.

1147.2006.05.1.0

13

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