PRODUCT DATASHEET
AAT2148
TM
SwitchReg
Low Noise, FastTransient 1A Step-Down Converter
Figure 2: AAT2148 Evaluation Board
Top Layer.
Figure 3: AAT2148 Evaluation Board
Bottom Layer.
U1
AAT2148
L1 4.7µH
VIN
12
11
10
9
13
14
15
VIN
VP
LX
LX
LX
VOUT
R1
267k
C1
4.7µF
VP
C2
10µF
C3
100pF
VP
4
8
VCC
FB
N/C
N/C
VIN
EN
7
R2
59k
EN
16
5
6
0
3
JP1
N/C
2
1
N/C
1
2
3
PGND
PGND
EP
PGND
Figure 4: AAT2148 Evaluation Board Schematic.
R2 set to either 59kΩ for good noise immunity or 221kΩ
for reduced no load input current.
Adjustable Output Resistor Selection
For applications requiring an adjustable output voltage,
the 0.6V version can be externally programmed. Resistors
R1 and R2 of Figure 4 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 sug-
gested value for 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 sensi-
tive to external noise and interference. Table 2 summa-
rizes the resistor values for various output voltages with
V
VREF
1.5V
0.6V
R3 =
OUT -1 · R4 =
- 1 · 59kΩ = 88.5kΩ
The adjustable version of the AAT2148, combined with
an external feedforward capacitor (C3 in Figure 1),
delivers enhanced transient response for extreme pulsed
load applications. The addition of the feedforward capac-
itor typically requires a larger output capacitor C2 for
stability.
w w w . a n a l o g i c t e c h . c o m
2148.2008.11.1.0
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