AAT1146 Datasheet, PDF (13/20 Pages) Advanced Analogic Technologies – Fast Transient 400mA Step-Down Converter

DATA SHEET
AAT1146
Fast Transient 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.
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
suggested value for R2 is 59k. 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 volt-
ages with R2 set to either 59k for good noise immu-
nity or 221k 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 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.
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