Product Specification
Power Supply Supervisor + Regulator + PWM
SG6105A
© System General Corp. - 13 - www.sg.com.tw • www.fairchildsemi.com
Version 1.0.1 (IAO33.0072.B0) September 25, 2007
Example of Using SG6105A for the ATX
Power Supply
Protection against over-voltage, short-circuit, and fault
conditions is mandatory in PC power supplies. These
protection circuits can be realized by using many discrete
components and comparators, which occupy a lot of PCB
space and add to assembling costs. This single chip
controller IC provides complete protection circuits, shunt
regulators, and PWM control function with fewer
components. SG6105A is an ideal controller IC for PC
switching mode power supplies.
The features and benefits of this device are:
Over-voltage and under-voltage protection for 3.3V,
5V, and 12V without external divider
Over-power protection
UV protection for –12V and/or –5V
Power-down warning for power-good signal
Power-good signal and power-fail lockup
Remote on / off c ont r o l
Delay tim e for PSON and PS-off signal
Two shunt regulators for 3.3V and 5V-standby
regulation
Complete pulse width modulation (PWM) control
circuitry
On-chi p o sci l lator
Programmable soft-start
Maximu m 93 % duty cycle
Few external components
More reliable system
Little space on PCB
Easy trouble-shooting and implementation
FEATURE DESCRIPTIONS
Over-voltage protection can be implemented
without any additional components. Over-voltage
sense levels for 3.3V, 5V, 12V, ar e 4.1V, 6. 1V,
14.5V, respectively.
Over-current and/or short-circuit protection can also
be achie ved usin g over-p ower prote ction, in which
the OPP pin is connected to the current transformer
(driver transformer).
The power-good signal is asserted to indicate the
3.3V, 5V, and 12 V is abo ve the under-voltage
threshold level. PG pin goes high when the above
condition is reached. A 2K pull-up resistor may
connect to 5V.
The V
CC
can be supplied from the 5V-standby.
When the V
CC
voltage is hi ghe r than 7V, besi de s
the shunt regulator, the circuit is shutdown and reset.
No extra power supply is needed.
Two in ternal high-pr ecision 431 shunt regulators ar e
built- in to provide stable reference voltages.
Complete PWM control circuitry, including the
error amplifier for push-pull or half-bridge
operation.
Supervisory Circuit Operation
The PC generates the remote ON/OFF logic
(PSON), which is “ Low” f or power s uppl y on a nd “High”
to switch off the power supply. The remote ON/OFF is
connected to PSON input.
APPLICATION GUIDES
Introduction
The application guide shows the key features of SG6105A
and illustrates how to design in an ATX switching mode
power supply (SMPS). SG6105A is suitable for
half-bridge, push-pull topology and incorporates with a
four-channel supervisor, including 5V-standby. The PWM
secti on of S G 610 5A c omp ri se s a bu ilt- i n 6 5kH z osc il la tor
and high-immunity circuits, which protect the system
from noise interference and provide more noise margins
for improper PCB layout. SG6105A has OVP and UVP
for 12V, 5 V, and 3.3 V. NVP is use d for ne gative vo ltage
protection, such as –12V and/or –5V. The UVAC (AC
fails detection) is applied to detect AC line condition.
Two built-in internal precision TL431 shunt regulators
can be used for 3.3V or 5V auxiliary standby power.
AC Fails Detection
Through a resistor divider, UVAC is connected to the
secondary power transformer for detecting the AC line
condition. Once the voltage of UVAC is lower than 0.7V
for a period of time, such as 200µs, the PG (power-good)
signal is pulled low to indicate an AC line power-down
condition. The voltage amplitude of the PWM switching