MAX1777/MAX1977/MAX1999
High-Efficiency, Quad Output, Main Power-
Supply Controllers for Notebook Computers
12 ______________________________________________________________________________________
Pin Description
MAX1999
NAME
FUNCTION
1 — CS3
3.3V SMPS Current-Sense Input. Connect CS3 to a current-sensing resistor from the source of
the synchronous rectifier to GND. The voltage at ILIM3 determines the current-limit threshold
(see the Current-Limit (ILIM) Circuit section).
— 1 N.C. No Connection. Not internally connected.
22
PGOOD
Power-Good Output. PGOOD is an open-drain output that is pulled low if either output is
disabled or is more than 10% below its nominal value.
3 3 ON3
3.3V SMPS Enable Input. The 3.3V SMPS is enabled if ON3 is greater than the SMPS on level
and disabled if ON3 is less than the SMPS off level. If ON3 is connected to REF, the 3.3V
SMPS starts after the 5V SMPS reaches regulation (delay start). Drive ON3 below the clear
fault level to reset the fault latches.
4 4 ON5
5V SMPS Enable Input. The 5V SMPS is enabled if ON5 is greater than the SMPS on level and
disabled if ON5 is less than the SMPS off level. If ON5 is connected to REF, the 5V SMPS
starts after the 3.3V SMPS reaches regulation (delay start). Drive ON5 below the clear fault
level to reset the fault latches.
55
ILIM3
3.3V SMPS Current-Limit Adjustment. The GND-LX current-limit threshold defaults to 100mV if
ILIM3 is tied to V
CC
. In adjustable mode, the current-limit threshold is 1/10th the voltage seen
at ILIM3 over a 0.5V to 3V range. The logic threshold for switchover to the 100mV default value
is approximately V
CC
- 1V. Connect ILIM3 to REF for a fixed 200mV threshold.
66
SHDN
Shutdown Control Input. The device enters its 6µA supply current shutdown mode if
V
SHDN
is less than the SHDN input falling edge trip level and does not restart until V
SHDN
is
greater than the SHDN input rising edge trip level. Connect SHDN to V+ for automatic startup.
SHDN can be connected to V+ through a resistive voltage-divider to implement a
programmable undervoltage lockout.
7 7 FB3
3.3V SMPS Feedback Input. Connect FB3 to GND for fixed 3.3V operation. Connect FB3 to a
resistive voltage-divider from OUT3 to GND to adjust the output from 2V to 5.5V.
8 8 REF
2V Reference Output. Bypass to GND with a 0.22µF (min) capacitor. REF can source up to
100µA for external loads. Loading REF degrades FB_ and output accuracy according to the
REF load-regulation error.
9 9 FB5
5V SMPS Feedback Input. Connect FB5 to GND for fixed 5V operation. Connect FB5 to a
resistive voltage-divider from OUT5 to GND to adjust the output from 2V to 5.5V.
10 10 PRO
Overvoltage and Undervoltage Fault Protection Enable/Disable. Connect PRO to V
CC
to
disable undervoltage and overvoltage protection. Connect PRO to GND to enable
undervoltage and overvoltage protection (see the Fault Protection section).
11 11
ILIM5
5V SMPS Current-Limit Adjustment. The GND-LX current-limit threshold defaults to 100mV if
ILIM5 is tied to V
CC
. In adjustable mode, the current-limit threshold is 1/10th the voltage seen
at ILIM5 over a 0.5V to 3V range. The logic threshold for switchover to the 100mV default value
is approximately V
CC
- 1V. Connect ILIM5 to REF for a fixed 200mV threshold.
12 12 SKIP
Low-Noise Mode Control. Connect SKIP to GND for normal idle-mode (pulse-skipping)
operation or to V
CC
for PWM mode (fixed frequency). Connect to REF or leave floating for
ultrasonic mode (pulse skipping, 25kHz minimum).
