sc1402 Semtech Corporation, sc1402 Datasheet - Page 10

• Manufacturer Part Number: sc1402
• Description: Multi-output, Low-noise Power Supply Controller For Notebook Computers
• Manufacturer: Semtech Corporation

inductor.
A heavy load on the 12OUT regulator when the 5V
SMPS is in PSAVE will cause the VDD input to drop,
browning out the regulator. If the output drops 0.8%
from its nominal value, the 5V SMPS is forced out of
PSAVE mode and into continuous conduction mode for
8 cycles. This recharges the bulk input capacitor on
VDD. The 12OUT linear regulator has a current limit to
prevent damage under short circuit conditions.
Over-voltage protection is provided on the VDD input.
If the VDD input is above 19V, an over-voltage is de-
tected and a 10mA current shunt load is applied to
VDD. The over-voltage threshold has 0.5V of hystere-
sis.
Power up Controls and Soft Start
The user has control of the SC1402 startup sequence
by setting the SEQ, RUN/ON3 and TIME/ON5 pins as
described in the following table.
© 2000 SEMTECH CORP.
December 15, 2000
REF
REF
REF
REF
GND
GND
VL
VL
SEQ
LOW
LOW
HIGH
HIGH
LOW
HIGH
LOW
HIGH
RUN/ON3
LOW
HIGH
LOW
HIGH
TIMING CAP
TIMING CAP
TIMING CAP
TIMING CAP
TIME/ON5
Follows 3.3V SMPS.
Low.
Follows 3.3V SMPS.
Follows 3.3V SMPS.
Low.
High after both outputs
are in regulation.
Low.
High after both outputs
are in regulation.
Multi-Output, Low-Noise Power Supply
Controller for Notebook Computers
RESET
652 MITCHELL ROAD
Each SMPS contains its own counter and DAC to grad-
ually increase the current limit at startup to prevent in-
put surge currents. The current limit is increased from
0, 20%, 40%, 60%, 80%, to 100% linearly over the
course of 512 switching cycles.
A RESET output is also generated at startup. The
RESET pin is held low for 32K switching cycles. An-
other timer is used to enable the undervoltage protec-
tion. The undervoltage protection circuitry is enabled
after 6144 switching cycles at which time the SMPS
should be in regulation.
When SEQ is set to REF, the RESET only monitors
the 3.3V SMPS in regulation. The 5V SMPS is ignored.
Independent start control mode.
Both SMPSs off.
5V SMPS ON, 3.3V SMPS OFF.
3.3V SMPS ON, 5V SMPS OFF.
Both SMPSs on.
Both SMPS off.
5V starts on rising edge of RUN/ON3, 3V
starts when TIME/ON5 > REF.
Both SMPS off.
3.3V starts on rising edge of RUN/ON3,
5V starts when TIME/ON5 > REF.
DESCRIPTION
NEWBURY PARK CA 91320
SC1402
10