FAN6103 Fairchild Semiconductor, FAN6103 Datasheet - Page 10

• Manufacturer Part Number: FAN6103
• Description: FAN6103 controller is designed for switching mode power supply for desktop PCs
• Manufacturer: Fairchild Semiconductor

© 2009 Fairchild Semiconductor Corporation
FAN6103 • Rev. 1.0.0
Functional Description
FAN6103 is suitable for half-bridge, push-pull topology
and incorporates with a three-channel supervisor. The
PWM section comprises a built-in 65KHz oscillator and
high-immunity circuits, which protect the system from
noise interference and provide more noise margins.
FAN6103 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 is applied to detect AC line
condition.
Over-Power Protection (OPP)
FAN6103 provides over-power protection to detect
over-power or short-circuit conditions. When it detects
the voltage level over 2.4V, the supervisor triggers PG
to LOW and pulls the SS pin LOW to switch off the
power.
Negative-Voltage Protection (NVP)
The NVP provides an under-voltage protection for
negative voltage output. An under-voltage represents
the phenomenal of the overload condition in negative
voltage output. For example, the -12V output may drop
to -10V during the overload situation. A resistor
determining the threshold of the protection is connected
from pin NVP to the negative voltage output. Via this
resistor, NVP output a 64µA constant current to the
negative voltage output. When the NVP voltage is over
2.1V for longer than 7ms, FAN6103 locks the power
output off:
The power outputs are locked off when V
V
NVP
=
64
Figure 17. OPP Protection Circuit
μ
A
×
(
R
1
+
V
R
DD
2
) ( 12 )
+ −
V
NVP
O P 1
O P 2
O P P
> 2.1V.
(1)
10
AC-Fail 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 signal is
pulled LOW to indicate an AC line power-down
condition. The voltage amplitude of the PWM switching
signal
proportional to the AC line voltage. Adjust the ratio of
resistor divider to determine the threshold of power-
down warning. A small capacitor is connected from
UVAC to ground for filtering the switching noise.
-1 2 V
in
Figure 18. NVP Protection Circuit
Figure 19. AC Detection Circuit
the
R
2
secondary
-5 V
R
1
5V
power
6 4µA
0. 7V
2 .1 V
transformer
+
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U V AC
is