AAT1147 AAT, AAT1147 Datasheet - Page 12

• Manufacturer Part Number: AAT1147
• Description: Step-Down Converter
• Manufacturer: AAT

The maximum output capacitor RMS ripple current
is given by:
Dissipation due to the RMS current in the ceramic
output capacitor ESR is typically minimal, resulting in
less than a few degrees rise in hot-spot temperature.
Output Resistor Selection
The output voltage of the AAT1147 0.6V version can
be externally programmed. Resistors R1 and R2 of
Figure 5 program the output to regulate at a voltage
12
Figure 2: AAT1147 Evaluation Board
I
RMS(MAX)
=
2
·
1
3
Top Side.
·
V
OUT
L · F
· (V
S
IN(MAX)
· V
Figure 4: AAT1147 Evaluation Board
IN(MAX)
- V
OUT
)
High Efficiency, Low Noise, Fast Transient
Bottom Side.
higher than 0.6V. To limit the bias current required for
the external feedback resistor string while maintain-
ing good noise immunity, the minimum suggested
value for R2 is 59kΩ. Although a larger value will fur-
ther 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 =
Figure 3: Exploded View of Evaluation
⎛
⎝
400mA Step-Down Converter
V
V
OUT
REF
-1 · R2 =
Board Top Side Layout.
⎞
⎠
⎛
⎝
1.5V
0.6V
- 1 · 59kΩ = 88.5kΩ
⎞
⎠
1147.2006.05.1.0