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AAT1153

2A Step-Down Converter

Advanced Analogic Technologies 

Applications Information

VIN 2.5V-5.5V

C1

22μF

1

EN

LX 8

2 IN

LX 7

3 AIN AAT1153-0.6 FB 5

6 AGND

4 AGND

PGND 10

PGND 9

L1

2.2μH

C3

22pF

VOUT

1.8V, 2A

R1

634kΩ C2

22μF

R2

316kΩ

Figure 1: Basic Application Circuit for the

Adjustable Output Version.

VIN 2.5V-5.5V

C1

22μF

1

EN

2 IN

LX 8

LX 7

3 AIN AAT1153-1.8 OUT 5

6 AGND

4 AGND

PGND 10

PGND 9

L1

2.2μH

VOUT

1.8V, 2A

C2

22μF

Figure 2: Basic Application Circuit for the Fixed

Output Versions.

Setting the Output Voltage

Figure 1 shows the basic application circuit with the

AAT1153 adjustable output version while Figure 2 shows

the application circuit with the AAT1153 fixed output ver-

sion. For applications requiring an adjustable output

voltage, the AAT1153-0.6 adjustable version can be

externally programmed. Resistors R1 and R2 in Figure 1

program the output to regulate at a voltage higher than

0.6V. To limit the bias current required for the external

feedback resistor string while maintaining good noise

immunity, the minimum suggested value for R2 is 59kΩ.

Although a larger value will further reduce quiescent cur-

rent, it will also increase the impedance of the feedback

node, making it more sensitive to external noise and

interference. Table 1 summarizes the resistor values for

various output voltages with R2 set to either 59kΩ for

good noise immunity or 316kΩ for reduced no load input

current.

The adjustable version of the AAT1153, combined with

an external feed forward capacitor (C3 in Figure 1),

delivers enhanced transient response for extreme pulsed

load applications. The addition of the feed forward

capacitor typically requires a larger output capacitor C2

PRODUCT DATASHEET

AAT1153

2A Step-Down Converter

for stability. The external resistor sets the output voltage

according to the following equation:

VOUT = 0.6V ·

⎛⎝1 +

R1 ⎞

R2 ⎠

R1 =

⎛

⎝

VOUT

0.6V

-

1 ⎞⎠

· R2

Table 1 shows the resistor selection for different output

voltage settings.

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 = 316kΩ

R1 (kΩ)

105

158

210

261

316

365

422

475

634

655

732

1000

1430

Table 1: Resistor Selections for Different Output

Voltage Settings (Standard 1% Resistors

Substituted For Calculated Values).

Inductor Selection

For most designs, the AAT1153 operates with inductor

values of 1μH to 4.7μH. Low inductance values are

physically smaller but require faster switching, which

results in some efficiency loss. The inductor value can

be derived from the following equation:

L = VOUT · (VIN - VOUT)

VIN · ΔIL · fOSC

Where ΔIL is inductor ripple current. Large value induc-

tors lower ripple current and small value inductors result

in high ripple currents. Choose inductor ripple current

approximately 30% of the maximum load current 2A, or

ΔIL = 600mA

1153.2008.02.1.2

www.analogictech.com

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