AN4003 Datasheet, PDF (1/28 Pages) Fairchild Semiconductor – PC POWER SUPPLY DESIGN WITH KA3511

November 2,1999
AN4003
PC POWER SUPPLY DESIGN WITH KA3511
Sang-Tae Im
1. GENERAL DESCRIPTION
The KA3511 is a fixed-frequency improved-performance pulse-width modulation control circuit with
complete housekeeping circuitry for use in the secondary side of SMPS (Switched mode power
supply). It contains various functions, which are precision voltage reference, over voltage protec-
tion, under voltage protection, remote on/off control, power good signal generator and etc.
OVP (Over voltage protection) section
It has OVP functions for +3.3V,+5V,+12V and PT outputs. The circuit is made up of a comparator
with four detecting inputs and without hysteresis voltage. Especially, PT (Pin16) is prepared for an
extra OVP input or another protection signal.
UVP (Under voltage protection) section
It also has UVP functions for +3.3V, +5V, +12V outputs. The block is made up of a comparator with
three detecting inputs and without hysteresis voltage.
Remote on/off section
Remote on/off section is used to control SMPS externally. If a high signal is supplied to the remote
on/off input, PWM signal becomes a high state and all secondary outputs are grounded. The
remote on/off signal is transferred with some on-delay and off-delay time of 8ms, 24ms respec-
tively.
Precision reference section
The reference voltage trimmed to ±2% (4.9V<Vref<5.1V)
PG (Power good signal generator) section
Power good signal generator is to monitor the voltage level of power supply for safe operation of a
microprocessor.
KA3511 requires few external components to accomplish a complete housekeeping circuits for
SMPS. The KA3511 is available in a 22-pin dual in-line package.
Rev C, November 1999
1