PRODUCT DATASHEET
AAT1146
SwitchRegTM
FastTransient 400mA Step-Down Converter
Figure 2: AAT1146 Evaluation Board
Top Side Layout.
Figure 3: Exploded View of Evaluation
Board Top Side Layout.
Figure 4: AAT1146 Evaluation Board
Bottom Side Layout.
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 5 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
V
1.5V
0.6V
⎛
⎝
⎞
⎛
⎝
⎞
⎠
R1 =
OUT -1 · R2 =
- 1 · 59kΩ = 88.5kΩ
⎠
REF
The adjustable version of the AAT1146, combined with
an external feedforward capacitor (C4 in Figure 5),
delivers enhanced transient response for extreme pulsed
load applications. The addition of the feedforward capac-
itor typically requires a larger output capacitor C1 for
stability.
w w w . a n a l o g i c t e c h . c o m
1146.2008.06.1.6
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