Product Specification
Power Supply Supervisor + Regulator + PWM
SG6105A
Example of Using SG6105A for the ATX
Power Supply
condition is reached. A 2K pull-up resistor may
connect to 5V.
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 VCC can be supplied from the 5V-standby.
When the VCC voltage is higher than 7V, besides
the shunt regulator, the circuit is shutdown and reset.
No extra power supply is needed.
Two internal high-precision 431 shunt regulators are
built-in to provide stable reference voltages.
Complete PWM control circuitry, including the
error amplifier for push-pull or half-bridge
operation.
The features and benefits of this device are:
Supervisory Circuit Operation
Over-voltage and under-voltage protection for 3.3V,
5V, and 12V without external divider
Over-power protection
The PC generates the remote ON/OFF logic
(PSON), which is “Low” for power supply on and “High”
to switch off the power supply. The remote ON/OFF is
connected to PSON input.
UV protection for –12V and/or –5V
Power-down warning for power-good signal
Power-good signal and power-fail lockup
Remote on/off control
APPLICATION GUIDES
Introduction
Delay time for PSON and PS-off signal
Two shunt regulators for 3.3V and 5V-standby
regulation
Complete pulse width modulation (PWM) control
circuitry
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
section of SG6105A comprises a built-in 65kHz oscillator
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, 5V, and 3.3V. NVP is used for negative voltage
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.
On-chip oscillator
Programmable soft-start
Maximum 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, are 4.1V, 6.1V,
14.5V, respectively.
AC Fails Detection
Over-current and/or short-circuit protection can also
be achieved using over-power protection, in which
the OPP pin is connected to the current transformer
(driver transformer).
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
The power-good signal is asserted to indicate the
3.3V, 5V, and 12V is above the under-voltage
threshold level. PG pin goes high when the above
© System General Corp.
Version 1.0.1 (IAO33.0072.B0)
- 13 -
www.sg.com.tw
•
www.fairchildsemi.com
September 25, 2007
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
