SG6105A Fairchild Semiconductor, SG6105A Datasheet - Page 11

• Manufacturer Part Number: SG6105A
• Description: SG6105A controller is designed for switching-mode power supplies for desktop PCs
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
SG6105A • Rev. 1.0.2
Functional Description
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:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
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 control.
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.
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.
11
Feature Descriptions
Supervisory Circuit Operation
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.
1.
2.
3.
4.
5.
6.
7.
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.
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).
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 condition is reached. A 2K pull-up
resistor may connect to 5V.
The V
When the V
besides the shunt regulator, the circuit is
shutdown and reset. No extra power supply is
needed.
Two
regulators
reference voltages.
Complete PWM control circuitry, including the
error amplifier for push-pull or half-bridge
operation.
CC
internal
can be supplied from the 5V-standby.
are
CC
voltage is higher than 7V,
high-precision
built-in
to
provide
431
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stable
shunt