Dual-Output Power-Supply
Controller for Notebook Computers
A synchronous rectifier at LX3 keeps efficiency high by
clamping the voltage across the rectifier diode.
Maximum current limit is set by an external low-value
sense resistor, which prevents excessive inductor cur-
rent during start-up or under short-circuit conditions.
Programmable soft-start is set by an optional external
capacitor; this reduces in-rush surge currents upon
start-up and provides adjustable power-up times for
power-supply sequencing purposes.
MAX786
V+
+5V LDO
LINEAR
REGULATOR
5V
P
3.3V
PWM
CONTROLLER
(SEE FIG. 3)
FB3
CS3
BST3
DH3
LX3
DL3
ON
SS3
VL
3.3V
REF
+3.3V
REFERENCE
ON
4.5V
SHDN
GND
PGND
4V
FAULT
ON3
FB5
2.8V
300kHz/200kHz
OSCILLATOR ON
STANDBY
5V
PWM
CONTROLLER
(SEE FIG. 3)
CS5
BST5
DH5
LX5
DL5
ON
SS5
SYNC
ON5
D1
VH
Q1
1.65V
D2
Q2
1.65V
Figure 2. MAX786 Block Diagram
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9
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
