FAN6206MY Fairchild Semiconductor, FAN6206MY Datasheet - Page 10

• Manufacturer Part Number: FAN6206MY
• Description: Primary & Secondary Side PWM Controllers Secondry Synchronous Rectifier
• Manufacturer: Fairchild Semiconductor

Specifications of FAN6206MY

• Operating Supply Voltage: 30 V
• Maximum Operating Temperature: + 105 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Output Voltage: 12 V
• Supply Current: 3 mA
• Package / Case: SOP-8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

© 2010 Fairchild Semiconductor Corporation
FAN6206 • Rev. 1.0.2
Function Description
Figure 29 and Figure 30 show the simplified circuit
diagram of a dual-forward converter and its key
waveforms. Switches Q
together. Once Q
applied across the transformer primary side and power
is delivered to the secondary side through the
transformer, powering D
magnetizing current linearly increases. When Q
are turned off, the magnetizing current of the
transformer forces the reset diodes (D
negative input voltage is applied across the transformer
primary side. During this time, magnetizing current
linearly decreases to zero and the secondary-side
inductor current freewheels through diode D
synchronous rectifier SR
diodes D
between drive signals for SR
Figure 30. Key Waveforms of Dual-Forward
Figure 29. Simplified Circuit Diagram of
1
and D
2
1
, it is important to have proper timing
and Q
Dual-Forward Converter
1
2
1
and Q
are turned on, input voltage is
and SR
Converter
1
. During this time, the
1
and SR
2
are turned on and off
2
are used instead of
2
.
R1
and D
2
1
. When
R2
and Q
) and
2
10
Figure 31 shows a typical application circuit. When a
dual-forward
conduction mode, the SR gate signals (GATE1 and
GATE2) are mainly controlled by SP and SN signals. SP
and SN signals are transferred through a pulse
transformer from XP and XN signals, which are
generated by FAN6210 (Primary-Side Synchronous
Rectifier Signal Trigger for Dual Forward Converter).
Figure 32 shows the timing diagram for continuous
conduction mode (CCM). Figure 33 shows the timing
diagram for discontinuous conduction mode (DCM).
The switching operation of SR MOSFETs Q
determined by the SN and SP signals. FAN6206 turns
on SR MOSFETs at the rising edge of the SP signal,
while it turns off the SR MOSFETs at the rising edge of
the SN signal. Within one switching cycle, SP and SN
are obtained two times.
With a voltage divider R
to secondary winding, R
to secondary winding, the PWM timing sequences and
frequency can be tracked precisely. The SR MOSFET is
turned on by SP signal only when the voltage level on
LPC1 or LPC2 pin is pulled LOW to GND.
During PWM-on period, the rectifying SR Q
by the rising edge of the SP signal after a propagation
delay (t
of the SN signal after a propagation delay (t
During PWM-off period, the freewheeling SR Q
turned on by the rising edge of the SP signal after a
propagation delay (t
the rising edge of the SN signal after a propagation
delay (t
In DCM operation, the proprietary Linear-Predict Timing
Control (LPC) technique can provide synchronous
rectification control mechanism for freewheeling SR
MOSFET. Since SN signal is sent following with PWM
signal, the freewheeling SR MOSFET cannot be turned
off in time by SN signal before I
zero. Therefore, the LPC mechanism is applied to turn
off Q
3
in DCM mode.
PD-HIGH-SP1
PD-LOW-SN2
Figure 31. Typical Application Circuit
converter
) in CCM operation.
) and Q
PD-HIGH-SP2
1
3
3
is turned off by the rising edge
and R
and R
operates
) and Q
2
4
Lo
connected from LPC1
connected from LPC2
linearly decreases to
4
in
is turned off by
3
www.fairchildsemi.com
is turned on
3
continuous
PD-LOW-SN1
and Q
4
4
is
is
).