AAT2500M Datasheet, PDF (16/22 Pages) Advanced Analogic Technologies – 400mA Step-Down Converter and 300mA LDO

AAT2500M
400mA Step-Down Converter and 300mA LDO
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.
R1
=
⎛ ^VOUT
⎝ V_REF
-1^⎞⎠
·
R2
=
⎛ ^1.5V
⎝ 0.6V
-
1 ^⎞⎠
·
59kΩ
=
88.5kΩ
The adjustable version of the AAT2500M, com-
bined 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.
V_OUT (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
R2 = 59kΩ
R1 (kΩ)
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
R2 = 221kΩ
R1 (kΩ)
75
113
150
187
221
261
301
332
442
464
523
715
Table 2: Adjustable Resistor Values For Use
With 0.6V Step-Down Converter.
VIN1
3
2
1
LDO Input
VOUT BUCK
C7
0.01µF
LX1
C1
4.7µF
L1
4.7µH
R1
C8
Table 2
n/a
GND
R2
C9
59k
n/a
U1
AAT2500M
1 _LX
IN_BUCK ¹²
2 _PGND
AGND ¹¹
3 _{EN_BUCK AGND} 10
4 _{EN_LDO}
AGND ⁹
5 _{FB_BUCK}
AGND ⁸
6 _{OUT_LDO IN_LDO} 7
C4
4.7µF
C3
10µF
C2
10µF
3
2
1
LDO Enable
3
2
1
Buck Enable
GND
VOUT LDO
Figure 5: AAT2500M Evaluation Board Schematic.
16
2500M.2007.06.1.0