Interleaved High-Efficiency, Dual Power-Supply
Controllers for Notebook Computers
CSH
0.05 x VLIMIT
0.1 x VLIMIT
CSL
SKIP
DECODE
SKIP
OSC
VLIMIT
-1.2 x VLIMIT
3mV
SLOPE COMP
AGND
R
Q
S
SOFT-START
SOFT-STOP
FB
REF / 2
ON
DH DRIVER
S
Q
R
DL DRIVER
Figure 3. PWM-Controller Functional Diagram
conduction” point). The load-current level at which
PFM/PWM crossover occurs, ILOAD(SKIP), is deter-
mined by:
ILOAD(SKIP)
=
(VIN − VOUT)VOUT
2LVIN ƒOSC
The switching waveforms may appear noisy and asyn-
chronous when light loading causes pulse-skipping
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-offs in PFM
noise vs. light-load efficiency are made by varying the
inductance. Generally, low inductance produces a
broader efficiency vs. load curve, while higher values
result in higher full-load efficiency (assuming that the
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