Preliminary
RT9277A/B
200× VOUT2 × C2
R3 =
C3 =
C4 =
L1
0.4×10-3 ×L1
V
IN
0.005 ×RESR ×L1
2
VOUT
The best criterion to optimize the loop compensation is
by inspecting the transient response and adjusting the
compensation network.
Soft-Start Capacitor
The soft-start function begins from VSS = 0V to VSS = 1.24V
with a 4μA constant current charging to the soft-start
capacitor, so the capacitor should be large enough to let
the output voltage reach regulation inside the soft-start
cycle. Typical value of soft-start capacitor range is from
10nF to 200nF. After the cycle finished, the load can start
to draw maximum current as required.
Layout Guideline
For high frequency switching power supplies, the PCB
layout is important step in system application design. In
order to let IC achieve good regulation, high efficiency and
stability, it is strongly recommended the power
components should be placed as close as possible. These
traces should be wide and short. The feedback pin and the
networks of feedback and compensation should keep away
from the power loops, and be shielded with a ground trace
or plane to prevent noise coupling.
DS9277A/B-02 March 2007
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11
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
