SG6108 데이터 시트보기 (PDF) - Fairchild Semiconductor
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SG6108 Datasheet PDF : 16 Pages
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Power Supply Supervisor + PWM
Product Specification
SG6108
Operation description
Protection against over-voltage, short-circuit and fault
conditions is mandatory for PC power supplies. Many
commonly used protection circuits require large numbers
of discrete components and comparators which occupy
significant PCB space and add to assembly costs. This
single chip controller IC provides complete protection,
shunt regulation, and PWM control with comparatively
few components. The SG6108 is an ideal controller IC for
PC switching mode power supplies. The features and
benefits of this device are listed on the first page.
Feature Notes
Over voltage protection can be implemented without
any additional components. Over-voltage sense
levels are 3.3V/5V/12V or 4.1V/6.1V/14.05V.
The SG6108’s over current protection monitors the
3.3V, 5V, and the two 12V levels. The voltage
difference across the external current shunt is used to
provide accurate OCP.
Over current and/or short circuit protection can also
be implemented by using over-power protection. To
do this, the OPP pin must be connected to the current
transformer (driver transformer).
The power good signal is asserted to indicate that the
3.3V/5V/12V signals are above the under voltage
threshold level. The PG pin goes high when the
above condition is reached. A 2kΩ pull up resistor
may be optionally connected to the 5V lead.
VCC can be supplied from the 5V-standby.
Whenever the VCC voltage exceeds 7V the entire
SG6108 will be shutdown and reset (except for the
shunt regulator). No extra power supply is needed.
Complete PWM control circuitry includes an error
amplifier for push-pull or half-bridge operation.
Application Guides
The application guide shows the key features of the
SG6108 and illustrates how to use it in an ATX switching
mode power supply (SMPS). The SG6108 is suitable for
half-bridge, push-pull topologies. The PWM section of
the SG6108 comprises a built-in 65kHz oscillator and
high immunity circuits, which protect the system from
noise interference and provide higher noise margins
against improper PCB layout. The SG6108 has OVP,
UVP, and OCP for the 3.3V and 5V signals, as wells as
both 12V signals. NVP is used for negative voltage
protection (–12V/–5V). UVAC (AC failure detection) is
used to measure the AC line voltage.
AC Failure Detection
UVAC is connected to the secondary power transformer
through a resistor divider. UVAC is used for detecting the
AC line voltage. Whenever the UVAC voltage drops
below 0.7V for a period of time such as 150usec, the PG
(power good) signal will be pulled low to indicate an AC
line power-down condition.
The voltage amplitude of the PWM switching signal in the
secondary power transformer is proportional to the AC
line voltage. The power-down warning threshold can be
controlled by adjusting the resistor-divider ratio. A small
VS
Vo
Vin
R1
R2
C1
+
0.7V
UVAC
Supervisory Circuit Operation
The PC generates the remote ON/OFF logic (PSON)
signal. When this is “Low” the power supply is “On”.
When it is “High”, the power supply is switched off. The
remote ON/OFF signal is supplied to the PSON input.
capacitor must be connected between UVAC and ground
to filter the switching noise.
Over Power Protection (OPP)
OPP (over power protection) is used to detect over power
and short-circuit conditions. Whenever the VOPP voltage
(p.7, Note-1) exceeds 2.3V for longer than 6msec the
SG6108 will pull PG low and lock off the power outputs.
© System General Corp.
Version 1.0.1 (IAO33.0048.B0)
- 12 -
www.sg.com.tw • www.fairchildsemi.com
September 26, 2007
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