AAT2500

1MHz Step-Down Converter/LDO Regulator

18

2500.2006.05.1.16

R2 is 59k

Ω. Although a larger value will further

reduce quiescent current, it will also increase the

impedance of the feedback node, making it more

sensitive to external noise and interference. Table 2

summarizes the resistor values for various output

voltages with R2 set to either 59k

Ω for good noise

immunity or 221k

Ω for reduced no load input current.

The adjustable version of the AAT2500, combined

with an external feedforward capacitor (C8 in

Figures 2 and 5), delivers enhanced transient

response for extreme pulsed load applications. The

addition of the feedforward capacitor typically

requires a larger output capacitor C1 for stability.

Table 2: Adjustable Resistor Values For Use

With 0.6V Step-Down Converter.

R2 = 59k

Ω

Ω

R2 = 221k

Ω

Ω

R1 (k

Ω

Ω)

R1 (k

Ω

Ω)

0.8

19.6

75

0.9

29.4

113

1.0

39.2

150

1.1

49.9

187

1.2

59.0

221

1.3

68.1

261

1.4

78.7

301

1.5

88.7

332

1.8

118

442

1.85

124

464

2.0

137

523

2.5

187

715

⎛⎞

⎝⎠

R1 =

⎛⎞

⎝⎠

1.5V

0.6V

Figure 5: AAT2500 Evaluation Board Schematic.

1. For step-down converter, enhanced transient configuration C8 = 100pF and C1 = 10uF.

Table 3

L1

C1

10μF

C2

GND

1

2

3

Buck Enable

LX1

GND

Table 3

R1

59k

R2

PGND

1

LX

2

VP

3

VCC

4

ENLDO

9

EN

10

FB

11

SGND

12

IN

5

OUT

6

GND

8

BYP

7

AAT2500

U1

4.7μF

C4

10μF

C3

10nF

C5

1

2

3

LDO Enable

1

2

3

LDO Input

0.01μF

C7

n/a

C9