FAN6208 Fairchild Semiconductor, FAN6208 Datasheet - Page 11

• Manufacturer Part Number: FAN6208
• Description: FAN6208 is a synchronous rectification (SR) controller for isolated LLC or LC resonant converters that can drive two individual SR MOSFETs emulating the behavior of rectifier diodes
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FAN6208 • Rev. 1.0.1
Green Mode
Switching frequency increases in LLC topology at light-
load condition, which increases the power consumption
for the SR gate drive. Green mode reduces power loss
at light load. FAN6208 has two ways to enable green
mode. Green mode is triggered when DETL voltage is
pulled LOW for less than 3.75µs (LF mode) or 1.90µs
(HF mode) for seven switching cycles. FAN6208
resumes normal SR gate driving when DETL voltage is
pulled LOW for longer than 3.75µs (LF mode) or 1.90µs
(HF mode) for seven switching cycles.
When DETL voltage is pulled HIGH for longer than
24µs. This occurs when the LLC resonant converter
operates in burst mode (skipping mode).
Short-Circuit Protection
As depicted in Figure 13, FAN6208 monitors the current
through the opto-coupler diode by measuring the
voltage across the resistor in series with the opto-
coupler diode. When the output of the power supply is
short circuited, the output voltage drops and the cathode
of the shunt regulator (KA431) is saturated to HIGH. No
current flows through the opto coupler diode. The output
short protection is triggered when the voltage between
V
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Figure 19. Output Short Protection by Feedback
and FD is smaller than 0.3V, as shown in Figure 19.
Detection
11
V
Over-voltage conditions are usually caused by an open
feedback loop. V
damage of SR MOSFET. When the voltage on the V
pin exceeds 27V, FAN6208 disables gate output.
Internal Over-Temperature Protection
Internal over-temperature protection prevents the SR
gate from fault triggering in high temperatures. If the
temperature is over 140°C, the SR gate is disabled until
the temperature drops below 120°C.
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Pin Over-Voltage Protection
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over-voltage protection prevents
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