AAT2500
1MHz Step-Down Converter/LDO Regulator
R2 is 59kΩ. 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 59kΩ for good noise
immunity or 221kΩ for reduced no load input current.
Ω
Ω
R2 = 221k
R2 = 59k
Ω
Ω
VOUT (V)
R1 (k )
R1 (k )
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
75
113
150
187
221
261
301
332
442
464
523
715
V
V
1.5V
0.6V
⎛
⎝
⎞
⎛
⎝
⎞
- 1 ·
R1 =
OUT -1
·
R2 =
59kΩ = 88.5kΩ
⎠
⎠
REF
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.
124
137
187
Table 2: Adjustable Resistor Values For Use
With 0.6V Step-Down Converter.
LX1
VOUTBUCK
R1
Table 3
C7
0.01μF
C9
n/a
U1
C81
AAT2500
PGND SGND
1
2
3
4
5
6
12
11
10
9
C1
4.7μF1
R2
59k
C2
10μF
LX
VP
FB
EN
L1
Table 3
3
2
1
VIN1
VCC ENLDO
3
2
1
Buck Enable
8
IN
GND
BYP
7
3
2
1
OUT
LDO Input
C3
10μF
C4
4.7μF
C5
10nF
LDO Enable
GND
GND
VOUTLDO
Figure 5: AAT2500 Evaluation Board Schematic.
1. For step-down converter, enhanced transient configuration C8 = 100pF and C1 = 10uF.
18
2500.2006.05.1.16
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
