FAN6204
mWSaver™ Synchronous Rectification Controller for
Flyback and Forward Freewheeling Rectification
Features
Description
mWSaver™ Technology:
Internal Green Mode to Stop SR Switching for
Lower No-Load Power Consumption
- 1.1 mA Ultra-Low Green Mode Operating
Current
SR Controller
Suited for Flyback Converter in QR, DCM, and
CCM Operation
Suited for Forward Freewheeling Rectification
PWM Frequency Tracking with Secondary-Side
Winding Voltage Detection
Ultra-Low VDD Operating Voltage for Various Output
Voltage Applications (5 V~24 V)
VDD Pin Over-Voltage Protection (OVP)
12 V (Typical) Gate Driver Clamp
FAN6204 is a secondary-side synchronous rectification
(SR) controller to drive SR MOSFET for improving
efficiency. The IC is suitable for flyback converters and
forward free-wheeling rectification.
FAN6204 can be applied in continuous or discontinuous
conduction mode (CCM and DCM) and quasi-resonant
(QR) flyback converters based on the proprietary
innovative linear-predict timing-control technique. The
benefits of this technique include a simple control
method without current-sense circuitry to accomplish
noise immunity.
With PWM frequency tracking and secondary-side
winding voltage detection, FAN6204 can operate in both
fixed- and variable-frequency systems.
In Green Mode, the SR controller stops all SR switching
operation to reduce the operating current. Power
consumption is maintained at minimum level in lightload condition.
8-Pin SOP Package
Applications
AC/DC NB Adapters
Open-Frame SMPS
Battery Charger
Ordering Information
Part Number
Operating
Temperature Range
Package
Packing Method
FAN6204MY
-40°C to +105°C
8-Pin, Small Outline Package (SOP)
Tape & Reel
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
www.fairchildsemi.com
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
February 2016
VIN
VOUT
ISR
VIN
VOUT
Q1
Q2
Q2
VDET
Q1
GATE VDD
3
R1
VLPC
LPC
8
RES
FAN6204
R2
R3
5
4
Q2
VRES
7
LPC
R4
6
R2
AGND
GND
R3
GATE VDD
3
R1
8
5
FAN6204
4
RES
R4
6
GND
Figure 1. Typical Application Circuit for
Flyback Converter
7
AGND
Figure 2. Typical Application Circuit for
Forward Freewheeling Rectification
Internal Block Diagram
GATE
3
VDD
Internal
Bias
5
950K
0.05VDD
+
50K
4.8V/4.5V
Calculate VLPC-EN
VLPC-EN
+
8
Rising
Edge
1µs
Blanking
+
0.05VDD
S
Drive
Q
PWM Block
6 AGND
R Q
+
VCT
Enable
RESET
iDISCHR
iCHR
tSR-MAX
Causal
Function
1 AGND
tDIS
-
Frequency
Tracking
Detector
Green
Mode
2 AGND
LPC
-
27.5V/25.4V
2V
OVP
5µA/V
1µA/V
CT
RESET
7
4
RES
GND
Figure 3. Functional Block Diagram
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
www.fairchildsemi.com
2
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
Application Diagrams
: Fairchild Logo
Z: Plant Code
X: Year Code
Y: Week Code
TT: Die Run Code
T: Package Type (N = DIP, M = SOP)
P: Y = Green Package
M: Manufacturing Flow Code
ZXYTT
6204
TPM
Figure 4. Marking Diagram
Pin Configuration
LPC
RES
AGND
VDD
8
7
6
5
1
2
3
4
AGND AGND GATE
GND
Figure 5. Pin Assignments
Pin Definitions
Pin #
Name
Description
1
AGND
Signal Ground
2
AGND
Signal Ground
3
GATE
Driver Output. The totem-pole output driver for driving the power MOSFET.
4
GND
Ground. MOSFET source connection.
5
VDD
Power Supply. The threshold voltages for startup and turn-off are 4.8 V and 4.5 V, respectively.
6
AGND
7
RES
Reset Control of linear predict. The RES pin is used to detect the output voltage level through a
voltage divider. An internal current source, IDISCHR, is modulated by the voltage level on the RES
pin.
8
LPC
Winding Detection. This pin is used to detect the voltage on the winding during the on-time
period of the primary GATE.
Signal Ground
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
www.fairchildsemi.com
3
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
Marking Information
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability.
The absolute maximum ratings are stress ratings only.
Symbol
Parameter
VDD
DC Supply Voltage
VL
LPC, RES
Min.
-0.3
Max.
Unit
30
V
7.0
V
Power Dissipation (TA=25°C)
0.82
Power Dissipation (TA=50°C)
0.65
ΘJA
Thermal Resistance (Junction-to-Air)
151
°C/W
ΘJC
Thermal Resistance (Junction-to-Case)
58
°C/W
TSTG
Storage Temperature Range
-55
+150
°C
TJ
Junction Temperature
-40
+150
ºC
TL
Lead Temperature (Soldering 10 Seconds)
+260
°C
PD
ESD
Human Body Model
5
Charged Device Model
2
W
kV
Notes:
1. Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device.
2. All voltage values, except differential voltages, are given with respect to GND pin.
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
www.fairchildsemi.com
4
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
Absolute Maximum Ratings
VDD=15 V and TA=25°C unless otherwise noted.
Symbol
VOP
Parameter
Conditions
Min.
Typ.
VDD-
Continuously Operating Voltage
OFF
Max.
Unit
28.5
V
VDD-ON
Turn-On Threshold Voltage
4.3
4.8
5.3
V
VDD-OFF
Turn-Off Threshold Voltage
4.0
4.5
5.0
V
VDD-HYST
VDD-ON – VDD-OFF
0.1
0.3
0.5
V
7
8
mA
1.1
1.3
mA
IDD-OP
IDD-GREEN
IDD-ST
VDD-OVP
Operating Current
VDD=15 V, LPC=50 kHz, MOSFET
CISS=6000 pF
Operating Current in Green Mode
VDD=15 V
Startup Current
VDD< VDD-ON
VDD Over-Voltage Protection
VDD-OVP-HYST Hysteresis Voltage for VDD OVP
tVDD-OVP
VDD OVP Debounce Time
150
200
A
26
27.5
28.5
V
1.8
2.1
2.4
V
40
70
100
s
10
12
Output Driver Section
VZ
Gate Output Clamp Voltage
VOL
Output Voltage Low
VDD=6 V, IO=50 mA
VOH
Output Voltage High
VDD=6 V, IO=50 mA
4
VDD=12 V, CL=6 nF, OUT=2 V~9 V
30
VDD=6 V, CL=6 nF, OUT=0.4 V~4 V
tR
Rising Time
tF
Falling Time
14
V
0.5
V
70
120
ns
70
120
170
ns
VDD=12 V, CL=6 nF, OUT=9 V~2 V
20
50
100
ns
VDD=6 V, CL=6 nF, OUT=4 V~0.4 V
20
90
130
ns
V
tPD_HIGH_LPC
Propagation Delay to Turn-on
Gate (LPC Trigger)
tR: 0 V~2 V, VDD=12 V
250
ns
tPD_LOW_LPC
Propagation Delay to Turn-off
(3)
Gate (LPC Trigger)
tF: 100%~90%, VDD=12 V
180
ns
tMAX-PERIOD
VPMOS-ON
VPMOS-ONHYS
tINHIBIT
VGATE-PULLHIGH
Limitation between LPC Rising Edge to Gate Falling Edge
Internal PMOS Turn-On to Pull-HIGH Gate
Hysteresis Voltage On
22.5
(3)
(3)
Gate Inhibit Time
M2 Option (Enable)
1.6
Gate Pull-HIGH Voltage
VDD=5 V
4.5
25.0
28.0
s
8.3
V
0.9
V
2.2
2.8
s
V
LPC Section
tBNK
Blanking Time for Charging CT
400
tDELAY-COMP Sampling Continuous Time for tBNK Compensation
(3)
500
600
ns
s
1
VLPC-SOURCE LPC Lower Clamp Voltage
Source ILPC=5 µA
0.1
0.2
0.3
V
ILPC-SOURCE LPC Source Current
VLPC=0 V
40
80
120
A
0.85
1.00
1.15
V
Threshold Voltage to Enabled SR
Switching
VLPC-EN=VLPC-HIGH x 0.83 at VLPCHIGH x 0.83< 2 V, VO=15 V,
VO=VDD, VLPC-HIGH=1.2 V
Threshold Clamp Voltage to
Enable SR Switching
VLPC-EN=2 V at VLPC-HIGH x 0.83 >
2V
VLPC-TH-HIGH
Threshold Voltage on LPC Rising
Edge
Decrease VLPC from 0.05
Vo+0.05, VO=15 V, VO=VDD
tBNK-DIS
Blanking Time at the Falling Edge
of VLPC
Prevent LPC Spike to Turn-Off
Gate
VLPC-EN
VEN-CLAMP
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
2
0.7
0.8
350
V
0.9
V
ns
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5
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
Electrical Characteristics
VDD=15 V and TA=25°C unless otherwise noted.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Unit
LPC Section (Continued)
(3)
VLPC-CLAMP-H Higher Clamp Voltage
6
VLPC-DIS
LPC Voltage to Disable SR Gate
tLPC-HIGH
Debounce Time for Disable SR Gate
4.0
tLPC-EN-RES
Debounce time to Reset VLPC-EN when LPC Signal is Absent
4.2
V
4.4
V
1
s
100
s
RES Section
VRES-EN
Threshold Voltage of VRES to Enable SR MOSFET
tRES-LOW
Debounce Time to Disable RES Function
0.60
(3)
0.75
0.90
V
1
2
µs
VRES-CLAMP-H Higher Clamp Voltage
6
V
KRES-DROP
RES Dropping Protection Ratio within One Cycle
90
%
tRES-DROP
Debounce Time for RES Voltage-Drop Protection
1.5
µs
Internal Timing Section
tCT
Linear Operation Range of CT
VLPC=1.5 V
27
30
33
s
VLPC-OP
Linear Operation Range of LPC to VDD5 V
0.8
3.4
V
0.8
4.0
V
VRES-OP
Linear Operation Range of RES to VDD5 V
0.8
3.4
V
0.8
4.0
V
RatioLPC-RES Ratio Between LPC and RES
4.65
5.00
1.1
tLPC-EN
Minimum LPC Time to Enable SR Switching, VLPC-HIGH>VLPC-EN
0.9
tgate-limit
ton-SR(n+1)< tgate-limitx ton-SR(n)
105
5.35
1.3
µs
120
%
Green Section
tGREEN-OFF
CT Capacitor tDIS Time to Leave
Green Mode
fS=65 kHz
4.60
5.35
6.10
µs
tGREEN-ON
CT Capacitor tDIS Time to Enter
Green Mode
fS=65 kHz
4.25
4.80
5.35
µs
Cycle Time to Enter Green Mode
CT Discharge Time < tGREEN-ON
3
Times
Cycle Time to Leave Green Mode
CT Discharge Time > tGREEN-OFF
7
Times
75
µs
120
%
tGREEN-TIMEenter
tGREEN-TIMEleave
tGREEN-ENTER No Gate Signal to Enter Green Mode
(3)
Causal Function Section
Once tS-PWM(n+1) > tCAUSALxtSPWM(n), SR Stops Switching and
Enter Green Mode
fS=65 kHz 40 kHz
tDEAD-CAUSAL
SR Turn-off Dead Time by Causal
Function
fS=65 kHz
tDEAD-CFR
Dead Time to Shrink SR ON Time
CFR (Causal Function Regulator)
tCAUSAL
tDEAD-RE-CFR SR ON Time Narrowed Down Width when tDEAD-CFR Triggered
380
580
780
ns
150
ns
1.5
s
140
°C
20
°C
Internal Over-Temperature Protection Section
TOTP
TOTP-HYST
Internal Threshold Temperature for OTP
(3)
Hysteresis Temperature for Internal OTP
(3)
Note:
3. Guaranteed by design.
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
www.fairchildsemi.com
6
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
Electrical Characteristics
Figure 6. Turn-On Threshold Voltage
Figure 7. Turn-Off Threshold Voltage
Figure 8. Startup Current
Figure 9. Operating Current
Figure 10. Operating Current in Green Mode
Figure 11. Gate Output Clamping Voltage
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
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7
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
Typical Performance Characteristics
Figure 12. LPC Source Current
Figure 13. LPC Lower Clamp Voltage
Figure 14. Threshold Voltage of VRES
Figure 15. Ratio between LPC and RES
Figure 16. Minimum LPC Enable Time
Figure 17. Maximum Period between LPC Rising Edge
to Gate Falling Edge
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
www.fairchildsemi.com
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FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
Typical Performance Characteristics (Continued)
Body diode of
SR MOSFET
Body diode of
SR MOSFET
Body diode of
SR MOSFET
VGS
Body diode of
SR MOSFET
VGS
Primary
MOSFET
Synchr onous Rectifier
MOSFET
Primary
MOSFET
VDET
Synchr onous Rectifier
MOSFET
Primary
MOSFET
VDET
VIN/n
VIN/n
VIN/n+VOUT
VIN/n+VOUT
VOUT
VLPC
VLPC-HIGH
VOUT
Blanking time
(tLPC-EN)
VLPC
VLPC-HIGH
0.83VLPC-HIGH
0.05VOUT
0.83VLPC-HIGH
0.05VOUT
IM,max
IM,max
IM
IM,av
IM
IDS
ISR /n
IDS
IM,min
IDS
ISR /n
IM,min
VCT
VCT
t PM.ON
t CT.DIS
t PM.ON
t CT.DIS
t L.DIS
t L.DIS
Figure 18. Typical Waveforms of Linear-Predict Timing Control in CCM and DCM/QR Flyback
FAN6204 uses the LPC and RES pins with two sets of
voltage dividers to sense DET voltage (VDET) and output
voltage (VOUT), respectively; so VIN/n, tPM.ON, and VOUT
can be obtained. As a result, tL,DIS , which is the on-time
of SR MOSFET, can be predicted by Equation (1). As
shown in Figure 18, the SR MOSFET is turned on when
the SR MOSFET body diode starts conducting and DET
voltage drops to zero. The SR MOSFET is turned off by
linear-predict timing control.
Linear Predict Timing Control
The SR MOSFET turn-off timing is determined by
linear-predict timing control and the operation principle
is based on the volt-second balance theorem. The voltsecond balance theorem states that the inductor
average voltage is zero during a switching period in
steady state, so the charge voltage and charge time
product is equal to the discharge voltage and discharge
time product. In flyback converters, the charge voltage
on the magnetizing inductor is input voltage (VIN), while
the discharge voltage is nVOUT, as the typical
waveforms show in Figure 18. The following equation
can be drawn:
VIN tPM .ON n VOUT tL.DIS
Circuit Realization
The linear-predict timing-control circuit generates a
replica (VCT) of magnetizing current of flyback
transformer using internal timing capacitor (CT), as
shown in Figure 19. Using the internal capacitor voltage,
the inductor discharge time (tL.DIS) can be detected
indirectly, as shown in Figure 18. When CT is discharged
to zero, the SR controller turns off the SR MOSFET.
(1)
where tPM,ON is inductor charge time and tL,DIS is
inductor discharge time.
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
www.fairchildsemi.com
9
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
Functional Description
VLPC-TH
VDET
Turn on SR Gate at
the falling edge
+
-
S
Turn off
VCT SR Gate
Q
The typical waveforms of CCM operation in steady state
are shown as Figure 18. When the primary-side
MOSFET is turned on, the energy is stored in Lm.
During the on-time of the primary-side MOSFET
(tPM.ON), the magnetizing current (IM) increases linearly
from IM,min to IM,max. Meanwhile, internal timing capacitor
(CT) is charged by current source (iCHR-iDICHR)
proportional to VIN, so VCT also increases linearly.
VOUT
SR Gate
R Q
R1
R3
LPC
iCHR
8
5µA/V
VCT
RES
iDISCHR
CT
7
1µA/V
R2
R
4
Figure 19. Simplified Linear-Predict Block
The voltage-second balance equation for the primaryside inductance of the flyback converter is given in
Equation (1). Inductor current discharge time is given
as:
tL.DIS
VIN tPM .ON
n VOUT
When the primary-side MOSFET is turned off, the
energy stored in Lm is released to the output. During the
inductor discharge time (tL.DIS), the magnetizing current
(IM) decreases linearly from IM,max to IM,min. At the same
time, the internal timing capacitor (CT) is discharged by
current source (iDISCHR) proportional to VOUT, so VCT also
decreases linearly. To guarantee the proper operation
of SR, it is important to turn off SR MOSFET just before
SR current reaches IM,min so that the body diode of SR
MOSFET conducts naturally during the dead time.
(2)
The voltage scale-down ratio between RES and LPC is
defined as K below:
K
R4 / R3 R4
R2 / R1 R2
DCM / QR Operation
(3)
In DCM / QR operation, when primary-side MOSFET is
turned off, the energy stored in Lm is fully released to
the output at the turn-off timing of primary-side
MOSFET. Therefore, the DET voltage continues
resonating until the primary-side MOSFET is turned on,
as depicted in Figure 18. While DET voltage is
resonating, DET voltage and LPC voltage drop to zero
by resonance, which can trigger the turn-on of the SR
MOSFET. To prevent fault triggering of the SR
MOSFET in DCM operation, blanking time is introduced
to LPC voltage. The SR MOSFET is not turned on even
when LPC voltage drops below 0.05 VOUT unless LPC
voltage stays above 0.83 VLPC-HIGH longer than the
blanking time (tLPC-EN). The turn-on timing of the SR
MOFET is inhibited by gate inhibit time (tINHIBIT), once
the SR MOSFET turns off, to prevent fault triggering.
During tPM.ON, the charge current of CT is iCHR-iDICHR,
while during tL.DIS, the discharge current is iDICHR. As a
result, the current-second balance equation for internal
timing capacitor (CT) can be derived from:
(
5 VIN
(
VOUT ) VOUT ) tPM .ON VOUT tCT .DIS
K n
(4)
Therefore, the discharge time of CT is given as:
5 VIN
(
VOUT ) VOUT ) tPM .ON
K
n
VOUT
(
tCT .DIS
(5)
When the voltage scale-down ratio between RES and
LPC (K) is five (5), the discharge time of CT (tCT.DIS) is
the same as inductor current discharge time (tL.DIS).
However, considering the tolerance of voltage divider
resistors and internal circuit, the scale-down ratio (K)
should be larger than five (5) to guarantee that tCT.DIS is
shorter than tL.DIS. It is typical to set K around 5~5.5.
mWSaver™ Technology
Green-Mode Operation
To minimize the power consumption at light-load
condition, the SR circuit is disabled when the load
decreases. As illustrated in Figure 20, the discharge
times of inductor and internal timing capacitor decrease
as load decreases. If the discharge time of the internal
timing capacitor is shorter than tGREEN-ON (around
4.8 µs) for more than three cycles, the SR circuit enters
Green Mode. Once FAN6204 enters Green Mode, the
SR MOSFET stops switching and the major internal
block is shut down to further reduce operating current of
the SR controller. In Green Mode, the operating current
reduces to 1.1 mA. This allows power supplies to meet
the most stringent power conservation requirements.
When the discharge time of the internal capacitor is
longer than tGREEN-OFF (around 5.35 µs) for more than
seven cycles, the SR circuit is enabled and resumes the
normal operation, as shown in Figure 21.
Referring to Figure 18; when LPC voltage is higher than
VLPC-EN over a blanking time (tLPC-EN) and lower than
VLPC-TH-HIGH (0.05 VOUT), then SR MOSFET can be
triggered. Therefore, VLPC-EN must be lager than VLPC-THHIGH or the SR MOSFET cannot be turned on. When
designing the voltage divider of LPC, R1 and R2 should
be considered as:
0.83
V
R2
( IN .MIN VOUT ) 0.05VOUT 0.3
R1 R2
n
(6)
On the other hand, the linear operation range of LPC
and RES (1~4 V) should be considered as:
V
R2
( IN .MAX VOUT ) 4
R1 R2
n
(7)
R4
VOUT 4
R3 R4
(8)
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
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10
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
CCM Operation
VLPC
Green Mode
Normal Mode
3 Times
tS-PWM (n-1)
4.8µs
4.8µs
4.8µs
tS-PWM (n)
> 1.2xtS-PWM (n-1)
VLPC
IM
Disable SR-Gate &
Enter Green Mode
SR_Gate
Figure 23. Fault Causal Timing Protection
Gate Expand Limit Protection
Gate expand limit protection controls on-time expansion
of the SR MOSFET. Once the discharge time of the
internal timing capacitor (tDIS.CT) is longer than 115% of
previous on time of the SR MOSFET (ton-SR(n-1));
ton-SR(n) is limited to 115% of ton-SR(n-1), as shown in
Figure 24. When output load changes rapidly from light
load to heavy load, voltage-second balance theorem
may not be applied. In this transient state, gate expand
limit protection is activated to prevent overlap between
SR gate and PWM gate.
Figure 20. Entering Green Mode
SR Gate
Green Mode
Normal Mode
7 Times
5.35µs
5.35µs
5.35µs
IM
ton-SR (n)
SR-gate is turned off by
=ton-SR (n-1)*115% Gate Limit protection
ton-SR (n-1)
…….
SR_Gate
tDIS.CT (n)
tDIS.CT (n-1)
VCT
Figure 21. Resuming Normal Operation
VLPC
Causal Function
Causal function is utilized to limit the time interval (tSRMAX) from the rising edge of VLPC to the falling edge of
the SR gate. tSR-MAX is limited to 97% of previous
switching period, as shown in Figure 22. When the
system operates at fixed frequency, whether voltagesecond balance theorem can be applied or not, causal
function can guarantee reliable operation.
VLPC
Rising
Edge
tS-PWM
Figure 24. Gate Expand Limit Protection
RES Voltage Drop Protection
RES voltage drop protection prevents VRES dropping too
much within a cycle. The VRES is sampled as a
reference voltage, VRES’, on VLPC rising edge. Once VRES
drops below 90% of VRES’ for longer than a debounce
time (tRES-DROP), the SR gate is turned off immediately,
as shown in Figure 25. When output voltage drops
rapidly within a switching cycle, voltage-second balance
may not be applied, RES dropping protection is
activated to prevent overlap.
Rising
Edge
tSR-MAX=tS-PWM*97%
VCT
SR_Gate
SR On-Time
TP1
TP1
SR Gate
is turned
off by
causal
function
t
RES-DROP
VRES
VRES’
0.9*VRES’
Figure 22. Causal Function Operation
VLPC
Fault Causal Timing Protection
Fault causal timing protection is utilized to disable the
SR gate under some abnormal conditions. Once the
switching period (tS-PWM(n)) is longer than 120% of
previous switching period (tS-PWM(n-1)), SR gate is
disabled and enters Green Mode, as shown in Figure
23. Since the rising edge of VLPC among switching
periods (tS-PWM) is tracked for causal function, the
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
SR_Gate
SR-Gate is turned
off immediately
Figure 25. VRES Dropping Protection
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11
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
accuracy of switching period is important. Therefore, if
the detected switching period has a serious variation
under some abnormal conditions, the SR gate should
be terminated to prevent fault trigger.
SR Gate
Under-Voltage Lockout (UVLO)
The power ON and OFF VDD threshold voltages are fixed
at 4.8 V and 4.5 V, respectively. With an ultra-low VDD
threshold voltage, FAN6204 can be used in various
output voltage applications.
LPC-Open Protection: If VLPC is higher than VLPC-DIS
(4.2 V) for longer than debounce time tLPC-HIGH,
FAN6204 stops switching immediately and enters
Green Mode. VLPC is clamped at 6 V to avoid LPC pin
damage.
VDD Pin Over-Voltage Protection (OVP)
Over-voltage conditions are usually caused by an open
feedback loop. VDD over-voltage protection prevents
damage on the SR MOSFET. When the voltage on VDD
pin exceeds 27.5 V, the SR controller stops switching
the SR MOSFET.
LPC-Short Protection: If VLPC is pulled to ground and
the charging current of timing capacitor (CT) is near
zero, so that SR gate is not output.
RES Pin Open / Short Protection
Over-Temperature Protection (OTP)
RES-Open Protection: If VRES is pulled to HIGH level,
the gate signal is extremely small and FAN6204 enters
Green Mode. In addition, VRES is clamped at 6V to avoid
RES pin damage.
To prevent SR gate from fault triggering in high
temperatures, internal over-temperature protection is
integrated in FAN6204. Once the temperature is over
140°C, SR gate is disabled until the temperature drops
below 120°C.
RES-Short Protection: If VRES is lower than VRES-EN
(0.7 V) for longer than debounce time tRES-LOW,
FAN6204 stops switching immediately and enters
Green Mode.
© 2014 Fairchild Semiconductor Corporation
FAN6204 • Rev. 1.4
www.fairchildsemi.com
12
FAN6204 —mWSaver™ Synchronous Rectification Controller for Flyback and Forward Freewheeling Rectification
LPC Pin Open / Short Protection
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The following includes registered and unregistered trademarks and service marks, owned by Fairchild Semiconductor and/or its global subsidiaries, and is not
intended to be an exhaustive list of all such trademarks.
F-PFS
FRFET®
SM
Global Power Resource
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Green FPS
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Gmax
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IntelliMAX
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Making Small Speakers Sound Louder
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®
®
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®
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Saving our world, 1mW/W/kW at a time™
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SMART START
Solutions for Your Success
SPM®
STEALTH
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SuperSOT-3
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Sync-Lock™
®*
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TRUECURRENT®*
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Definition of Terms
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Advance Information
Formative / In Design
Preliminary
First Production
No Identification Needed
Full Production
Obsolete
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Definition
Datasheet contains the design specifications for product development. Specifications may change
in any manner without notice.
Datasheet contains preliminary data; supplementary data will be published at a later date. Fairchild
Semiconductor reserves the right to make changes at any time without notice to improve design.
Datasheet contains final specifications. Fairchild Semiconductor reserves the right to make
changes at any time without notice to improve the design.
Datasheet contains specifications on a product that is discontinued by Fairchild Semiconductor.
The datasheet is for reference information only.
Rev. I77
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