AAT1153_08 datasheet(11/19 Pages) ANALOGICTECH

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AAT1153

2A Step-Down Converter

PRODUCT DATASHEET

1153.2008.02.1.2

www .analogictech.com

Applications Information

PGND

AIN

AGND

AAT1153-0.6

22μF

VIN 2.5V-5.5V

2.2μH

22pF

22μF

634k

316k

VOUT

1.8V, 2A

AGND

Figure 1: Basic Application Circuit for the

Adjustable Output Version.

PGND

AIN

AGND

OUT

AAT1153-1.8

22μF

VIN 2.5V-5.5V

2.2μH

22μF

VOUT

1.8V, 2A

AGND

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

for stability. The external resistor sets the output voltage

according to the following equation:

⎛⎞

VOUT = 0.6V · 1 +

⎝⎠

⎛⎞

R1 =

- 1 · R2

⎝⎠

VOUT

0.6V

Table 1 shows the resistor selection for different output

voltage settings.

VOUT (V)

R2 = 59kΩ

R1 (kΩ)

R2 = 316kΩ

R1 (kΩ)

0.8

19.6

105

0.9

29.4

158

1.0

39.2

210

1.1

49.9

261

1.2

59.0

316

1.3

68.1

365

1.4

78.7

422

1.5

88.7

475

1.8

118

634

1.85

124

655

2.0

137

732

2.5

187

1000

3.3

267

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:

VOUT · (VIN - VOUT)

VIN · ΔIL · fOSC

L =

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

ΔI

L = 600mA

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