FAN6208 Fairchild Semiconductor, FAN6208 Datasheet - Page 8
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FAN6208
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
Datasheet
1.FAN6208.pdf
(18 pages)
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
FAN6208MY
Manufacturer:
FAIRCHILD/仙童
Quantity:
20 000
© 2010 Fairchild Semiconductor Corporation
FAN6208 • Rev. 1.0.1
Function Description
Operation Principle
FAN6208 is a secondary-side synchronous rectifier
controller for LLC or LC resonant converters that drive
two synchronous rectifier MOSFETs. Figure 7 is the
simplified circuit diagram of an LLC converter. The
FAN6208 determines SR MOSFET turn-on/off timing by
detecting the drain-to-source voltage of each SR
MOSFET. The key waveforms for LLC resonant
converter for below resonance and above resonance
are shown in Figure 8 and Figure 9, respectively.
Figure 8.
LLC Resonant Converter
Figure 7.
V
IN
Cr
Lr
Key Waveforms of LLC Resonant Converter for
I
P
L
m
Simplified Schematic of LLC Converter
Below Resonance Operation
Secondary-Side Synchronous Rectifiers
DETL1 GATE1
DETL2
RP
FD
FAN6208
GATE2
GND
VDD
SR1
SR2
V
O
8
Timing Estimator
Figure 10 shows the timing diagram for FAN6208. Once
the body diode of SR begins conducting, the drain-to-
source voltage drops to zero, which causes DETL pin
voltage to drop to zero. FAN6208 turns on the MOSFET
after t
drops below 2V. As depicted in Figure 11, the turn-on
delay (after t
(150ns) and propagation delay (200ns).
FAN6208 measures the SR conduction duration (t
during which DETL stays lower than 2V, and uses this
information to determine the turn-off instant of SR gates
of the next switching cycle. The turn-off timing is
obtained by subtracting a dead time (t
measured SR conduction duration of the previous
switching cycle. The dead time can be programmed
using a resistor on the RP pin and the relationship
between the dead time and SR conduction duration
(t
Figure 5.
Figure 9.
DETL
) for different resistor values on RP pin is given in
ON-ON-DETL
Key Waveforms of LLC Resonant Converter for
SR-ON-DETL
(about 350ns), when voltage on DETL
Above Resonance Operation
) is the sum of debounce time
DEAD
www.fairchildsemi.com
) from the
DETL
),