AAT2146 Datasheet, PDF (13/19 Pages) Advanced Analogic Technologies – Low Noise, Fast Transient 600mA Step-Down Converter

SwitchReg^TM
PRODUCT DATASHEET
AAT2146
Low Noise, Fast Transient 600mA Step-Down Converter
Figure 2: AAT2146 Evaluation Board
Component Side Layout.
Figure 3: Exploded View of AAT2146
Evaluation Board Component Side Layout.
Figure 4: AAT2146 Evaluation Board
Solder 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 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
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 AAT2146, combined with
an external feedforward capacitor (C4 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 C1 for
stability.
2146.2008.04.1.1
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