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MIC2165 Datasheet, PDF (19/27 Pages) Micrel Semiconductor – Adaptive On-Time DC-DC Controller Featuring Hyper Light Load | |||
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Micrel, Inc.
Figure 9a.
R2
R1+ R2
Ã
ÎVOUT
> 20mV
Figure
9b.
R2
R1 + R2
Ã
ÎVOUT
<
20mV and
Î VOUT
>
20mV
MIC2165
The process of sizing the ripple injection resistor and
capacitors is:
Step 1. Select Cff to feed all output ripples into the
feedback pin and make sure the large time constant
assumption is satisfied. Typical choice of Cff is 1nF to
100nF if R1 and R2 are in k⦠range.
Step 2. Select Rinj according to the expected feedback
voltage ripple. According to the equation (39),
K div
=
ÎVFB(PP)
VIN
à fSW à Ï
D Ã (1 â D)
(41)
Then the value of Rinj is obtained as:
R inj
= (R1// R2) Ã ( 1
K div
â 1)
(42)
Step 3. Select Cinj as 100nF, which could be considered
as short for a wide range of the frequencies.
Figure 9c. ÎVOUT < 20mV
June 2010
19
M9999-060810-D
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