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FAN6921AML
Integrated Critical Mode PFC / Quasi-Resonant
Current Mode PWM Controller
Features
Description
The highly integrated FAN6921AML combines a Power
Factor Correction (PFC) controller and a QuasiResonant PWM controller. Integration provides costeffect design and allows for fewer external components.
Integrated PFC and Flyback Controller
Critical Mode PFC Controller
Zero-Current Detection for PFC Stage
Quasi-Resonant Operation for PWM Stage
Internal Minimum toff 8 µs for QR PWM Stage
Internal 10 ms Soft-Start for PWM
Brownout Protection
H/L Line Over-Power Compensation (OPC)
Latched Protection (FB Pin)
Over-Power / Overload Protection
Short-Circuit Protection
Open-Loop Protection
Externally Latch Triggering (RT Pin)
Adjustable Over-Temperature Latched (RT Pin)
VDD Pin & Output Voltage OVP (Latched)
Internal Temperature Shutdown (140°C)
For PFC, FAN6921AML uses a controlled on-time
technique to provide a regulated DC output voltage and
to perform natural power factor correction. With an
innovative THD optimizer, FAN6921AML can reduce
input current distortion at zero-crossing duration to
improve THD performance.
For PWM, FAN6921AML enhances the power system
performance through valley detection, green-mode
operation, and high / low line over power compensation.
FAN6921AML provides: secondary-side open-loop and
over-current protection, external latch triggering,
adjustable over-temperature protection by RT pin and
external NTC resistor, internal over-temperature
shutdown, VDD pin OVP, and DET pin over-voltage for
output OVP, and brownin / out for AC input voltage
under-voltage protection (UVP).
The FAN6921AML controller is available in a 16-pin
small outline package (SOP).
Applications
AC/DC NB Adapters
Open-Frame SMPS
Battery Charger
Ordering Information
Part Number
OLP Mode
Operating
Temperature Range
Package
Packing
Method
FAN6921AMLMY
Latch
-40°C to +105°C
16-Pin Small Outline Package (SOP)
Tape & Reel
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Current Mode PWM Controller
May 2013
14
6
ZCD
13
4
1
3
16
OPFC CSPFC INV RANGE HV
NC
VIN
FAN6921
GND
OPWM
15
8
9
COMP
2
RT
FB
12
11
DET VDD
10
7
Figure 1. Typical Application
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
CSPWM
5
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Application Diagram
www.fairchildsemi.com
2
COMP
HV
VDD
2
16
7
RANGE
Multi-Vector Amp.
2.65V
2.75V
RANGE
2.75V
2.9V
Internal
Bias
OVP
IHV
OVP
27.5V
Latched
UVP
2.3V
NC
6
OPFC
DRV
Debounce
70µs
0.45V
15
Two Steps
UVLO
18V/10V/7.5V
S
SET
Q
15.5V
INV
Latched
3
2.5V
CLR
Q
2.1V/1.75V
Inhibit
Timer
0.2V
Blanking
Circuit
4
PFC Zero Current
Detector
Disable
Function
PFC
Current Limit
0.6V
Restarter
Sawtooth
Generator
/tON-MAX-PFC
THD
Optimizer
CSPFC
R
Brownout
VC & PFC ON/OFF &
Multi Vector Amp.
ON/OFF
Debounce
550ms / 150µs
VCTL-PFC-ON/OFF
14
0.7V
Timer
50ms
4.2V
FB
11
VB
2.5ms
32.5µs
2R
Soft-Start
9.5ms
FB OLP
Starter
DRV
R
S
CSPWM
5
Blanking
Circuit
PWM
Current Limit
IDET
Valley
Detector
1st Valley
S/H
8
OPWM
1
RANGE
tOFF-MIN
+9µs
Lathed
Protection
Startup
VB & clamp
VCOMP to 1.6V
Latched
Debounce
Time
DET OVP
IRT
0.8V VINV VINV
0.3V
IDET
1V/1.2V
Brownout
comparator
Debounce
100ms
100us
10ms
0.5V
Latched
Debounce
100ms
1.2V
0.8V
100uA
Internal
OTP
Q
Latched
VDET
2.5V
10
CLR
(RT Pin) Prog. OTP
Brownout
(RT Pin) Externally Triggering
Protection
Output Short Circuit (FB
Latched
Pin)
Output Open-Loop (FB Pin)
Output Over Power/ Overload (FB Pin)
VC
5V
Q
DET pin OVP
VDD pin OVP
Internal OTP
IDET
tOFF-MIN
(8us/37µs/2.5ms)
DET
SET
17.5V
R
Over Power
Compensation
tOFF
Blanking
(4µs)
ZCD
10V
IZCD
Prog. OTP
/ Externally Triggering
2.35V/2.15V
9
12
13
GND
RT
VIN
PFC RANGE Control
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Internal Block Diagram
Figure 2. Functional Block Diagram
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
3
16
- Fairchild Logo
Z - Plant Code
X - Year Code (1 Digit for SOP, 2-Digit for DIP)
Y - Week Code (1 Digit for SOP, 2-Digit for DIP)
TT – Die-Run Code
F - Frequency (M=LOW, H=HIGH Level)
O - OLP Mode (L=Latch, R=Recovery)
T - Package Type (N=DIP, M=SOP)
P – Y=Green Package
M - Manufacture Flow Code
ZXYTT
FAN6921AFO
TPM
1
Figure 3. Marking Diagram
Pin Configuration
RANGE
1
16
HV
COMP
2
15
N.C.
3
14
ZCD
CSPFC
4
13
VIN
CSPWM
5
12
RT
OPFC
6
11
FB
VDD
7
10
DET
OPWM
8
9
GND
INV
Figure 4. Pin Configuration
Pin Definitions
Pin #
Name
Description
1
RANGE
RANGE pin’s impedance changes according to the VIN pin voltage level. When the input
voltage detected by the VIN pin is lower than a threshold voltage, it sets to high impedance;
whereas it sets to low impedance if input voltage is high level.
2
COMP
Output pin of the error amplifier. It is a transconductance type error amplifier for PFC output
voltage feedback. Proprietary multi-vector current is built-in to this amplifier; therefore, the
compensation for the PFC voltage feedback loop allows a simple compensation circuit between
this pin and GND.
3
INV
Inverting input of the error amplifier. This pin is used to receive PFC voltage level by a voltage
divider and provides PFC output over- and under-voltage protections.
CSPFC
Input to the PFC over-current protection comparator that provides cycle-by-cycle current limiting
protection. When the sensed voltage across the PFC current-sensing resistor reaches the
internal threshold (0.6 typical), the PFC switch is turned off to activate cycle-by-cycle current
limiting.
5
CSPWM
Input to the comparator of the PWM over-current protection and performs PWM current-mode
control with FB pin voltage. A resistor is used to sense the switching current of the PWM switch
and the sensing voltage is applied to the CSPWM pin for the cycle-by-cycle current limit, currentmode control, and high / low line over-power compensation according to DET pin source current
during PWM on time.
6
OPFC
Totem-pole driver output to drive the external power MOSFET. The clamped gate output voltage
is 15.5 V.
4
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Marking Information
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
4
Pin #
Name
7
VDD
8
OPWM
9
GND
Description
Power supply. The threshold voltages for startup and turn-off are 18 V and 7.5 V, respectively.
The startup current is less than 30 µA and the operating current is lower than 10 mA.
Totem-pole output generates the PWM signal to drive the external power MOSFET. The
clamped gate output voltage is 17.5 V.
The power ground and signal ground.
This pin is connected to an auxiliary winding of the PWM transformer through a resistor divider
for the following purposes:
Producing an offset voltage to compensate the threshold voltage of PWM current limit for
providing over-power compensation. The offset is generated in accordance with the input
voltage when PWM switch is on.
10
DET
Detecting the valley voltage signal of drain voltage of the PWM switch to achieve the valley
voltage switching and minimize the switching loss on the PWM switch.
Providing output over-voltage protection. A voltage comparator is built-in to the DET pin. The
DET pin detects the flat voltage through a voltage divider paralleled with auxiliary winding.
This flat voltage is reflected to the secondary winding during PWM inductor discharge time. If
output OVP and this flat voltage is higher than 2.5 V, the controller enters latch mode and
stops all PFC and PWM switching operation.
11
FB
Feedback voltage pin. This pin is used to receive the output voltage level signal to determine
PWM gate duty for regulating output voltage. The FB pin voltage can also activate open-loop,
overload, or output-short-circuit protection if the FB pin voltage is higher than a threshold of
around 4.2 V for more than 50 ms.The input impedance of this pin is a 5 kΩequivalent
resistance. A 1/3 attenuator is connected between the FB pin and the input of the CSPWM/FB
comparator.
12
RT
Adjustable over-temperature protection and external latch triggering. A constant current flows
out of the RT pin. When RT pin voltage is lower than 0.8 V (typical), latch mode protection is
activated and stops all PFC and PWM switching operation until the AC plug is removed.
13
VIN
Line-voltage detection for brownin/out protections. This pin can receive the AC input voltage
level through a voltage divider. The voltage level of the VIN pin is not only used to control
RANGE pin’s status, but it can also perform brownin/out protection for AC input voltage UVP.
14
ZCD
Zero-current detection for the PFC stage. This pin is connected to an auxiliary winding coupled
to PFC inductor winding to detect the ZCD voltage signal once the PFC inductor current
discharges to zero. When the ZCD voltage signal is detected, the controller starts a new PFC
switching cycle. When the ZCD pin voltage is pulled to under 0.2 V (typical), it disables the PFC
stage and the controller stops PFC switching. This can be realized with an external circuit if
disabling the PFC stage is desired.
15
NC
No connection
16
HV
High-voltage startup. HV pin is connected to the AC line voltage through a resistor (100 kΩ
typical) for providing a high-charging current to VDD capacitor.
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Pin Definitions
www.fairchildsemi.com
5
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
Min.
Max.
Unit
30
V
VDD
DC Supply Voltage
VHV
HV
500
V
VH
OPFC, OPWM
-0.3
25.0
V
VL
Others (INV, COMP, CSPFC, DET, FB, CSPWM, RT)
-0.3
7.0
V
Input Voltage to ZCD Pin
-0.3
12.0
V
VZCD
PD
Power Dissipation
800
mW
JA
Thermal Resistance; Junction-to-Air
104
°C/W
JC
Thermal Resistance; Junction-to-Case
41
°C/W
TJ
TSTG
TL
ESD
Operating Junction Temperature
-40
+150
°C
Storage Temperature Range
-55
+150
°C
+260
°C
Lead Temperature; Soldering 10 Seconds
Human Body Model, JESD22-A114 (All Pins Except HV Pin)
(3)
Charged Device Model, JESD22-C101 (All Pins Except HV Pin)
4500
(3)
1250
V
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 the GND pin.
3. All pins including HV pin: CDM=500 V, HBM=1000 V.
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to Absolute Maximum Ratings.
Symbol
TA
Parameter
Operating Ambient Temperature
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
Min.
Max.
Unit
-40
+105
°C
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Absolute Maximum Ratings
www.fairchildsemi.com
6
VDD=15 V, TA=-40~105°C (TA=TJ), unless otherwise specified.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
25
V
VDD Section
VOP
Continuously Operating Voltage
VDD-ON
Turn-On Threshold Voltage
16.5
18.0
19.5
V
VDD-PWM-OFF
PWM Off Threshold Voltage
9
10
11
V
VDD-OFF
Turn-Off Threshold Voltage
6.5
7.5
8.5
V
10
20
µA
10
mA
IDD-ST
Startup Current
VDD=VDD-ON - 0.16 V,
Gate Open
IDD-OP
Operating Current
VDD=15 V, OPFC;
OPWM=100 KHz;
CL-PFC, CL-PWM=2 nF
Green Mode Operating Supply
Current (Average)
VDD=15 V,
OPWM=450 Hz,
CL-PWM=2 nF
IDD-GREEN
IDD-PWM-OFF
Operating Current at PWM-OFF VDD=VDD-PWM-OFF Phase
0.5 V
5.5
mA
70
120
170
µA
VDD-OVP
VDD Over-Voltage Protection (Latch-Off)
26.5
27.5
28.5
V
tVDD-OVP
VDD OVP Debounce Time
100
150
200
µs
IDD-LATCH
VDD OVP Latch-up Holding
Current
VDD=7.5 V
120
µA
HV Startup Current Source Section
VHV-MIN
IHV
Minimum Startup Voltage on HV Pin
Supply Current from Pin HV
50
V
VAC=90 V
(VDC=120 V), VDD=0 V
1.2
mA
HV=500 V,
VDD= VDD-OFF +1 V
1.0
µA
VIN and RANGE Section
VVIN-UVP
VVIN-RE-UVP
tVIN-UVP
The Threshold Voltage for AC Input Under-Voltage
Protection
Under-Voltage Protection Reset Voltage (for Startup)
Under-Voltage Protection Debounce Time (No Need at
Startup/Hiccup Mode)
0.95
1.00
1.05
V
VVIN-UVP
+0.15 V
VVIN-UVP
+0.2 V
VVIN-UVP
+0.25 V
V
70
100
130
ms
VVIN-RANGE-H
High VVIN Threshold for RANGE
RANGE=Ground
Comparator
2.30
2.35
2.40
V
VVIN-RANGE-L
Low VVIN Threshold for RANGE
RANGE=Open
Comparator
2.10
2.15
2.20
V
70
100
130
ms
0.5
V
28
µs
tRANGE
Range-Enable/Disable Debounce Time
VRANGE-OL
Output Low Voltage of RANGE
Pin
tON-MAX-PFC
PFC Maximum On Time
IO=1 mA
22
25
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Electrical Characteristics
Continued on the following page…
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
7
VDD=15 V, TA=-40~105°C (TA=TJ), unless otherwise specified.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
100
125
150
µmho
2.465
2.500
2.535
V
RANGE=Open
2.70
2.75
2.80
V
RANGE=Ground
2.60
2.65
2.70
V
VINVH / VREF,
RANGE=Open
1.06
1.14
VINVH / VREF,
RANGE=Ground
1.04
1.08
PFC Stage
Voltage Error Amplifier Section
(4)
Gm
Transconductance
VREF
Feedback Comparator Reference Voltage
VINV-H
Clamp High Feedback Voltage
VRATIO
VINV-L
Clamp High Output Voltage Ratio
Clamp Low Feedback Voltage
2.25
2.30
2.35
V
RANGE=Open
2.90
2.95
V
RANGE=Ground
2.75
2.80
V
50
70
90
µs
0.35
0.45
0.55
V
VINV-OVP
Over Voltage Protection for INV
Input
tINV-OVP
Over-Voltage Protection Debounce Time
VINV-UVP
Under-Voltage Protection for INV Input
tINV-UVP
Under Voltage Protection Debounce Time
50
70
90
µs
INV Threshold Voltage for Blocking FB latch
0.7
0.8
0.9
V
VINV-BO
PWM and PFC Off Threshold for Brownout Protection
1.15
1.20
1.25
V
VINV-BO2
PWM Off Threshold Voltage for Brownout Protection,
PFC Off
0.7
0.8
0.9
V
Comparator Output High Voltage
4.8
6.0
V
Zero Duty Cycle Voltage on COMP Pin
1.15
1.25
1.35
V
15
25
35
µA
0.50
0.75
1.00
mA
RANGE=Open,
VINV=2.75 V, VCOMP=5
20
30
40
µA
RANGE=Ground,
VINV=2.65V, VCOMP=5
20
30
40
µA
VINV-FB-Latch
VCOMP
VOZ
Comparator Output Source
Current
ICOMP
Comparator Output Sink Current
VINV=2.3 V, VCOMP=1.5
VINV=1.5 V
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Electrical Characteristics (Continued)
PFC Current Sense Section
VCSPFC
Threshold Voltage for Peak
Current Cycle-by-Cycle Limit
VCOMP=5 V
tPD
Propagation Delay
tBNK
Leading-Edge Blanking Time
AV
CSPFC Compensation Ratio for THD
0.60
V
110
200
ns
110
180
250
ns
0.90
0.95
1.00
Continued on the following page…
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
8
VDD=15 V, TA=-40°C~105°C (TA=TJ), unless otherwise specified.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Unit
PFC Output Section
VZ
PFC Gate Output Clamping
Voltage
VDD=25 V
VOL
PFC Gate Output Voltage Low
VDD=15 V, IO=100 mA
VOH
PFC Gate Output Voltage High
VDD=15 V, IO=100 mA
8
tR
PFC Gate Output Rising Time
VDD=12 V, CL=3 nF,
20~80%
30
65
100
ns
tF
PFC Gate Output Falling Time
VDD=12 V, CL=3 nF,
80~20%
30
50
70
ns
Input Threshold Voltage Rising
Edge
VZCD Increasing
1.9
2.1
2.3
V
VZCD-HYST
Threshold Voltage Hysteresis
VZCD Decreasing
0.25
0.35
0.45
V
VZCD-HIGH
Upper Clamp Voltage
IZCD=3 mA
8
10
VZCD-LOW
Lower Clamp Voltage
IZCD=-1.5 mA
0.55
0.70
0.85
V
VZCD-SSC
Starting Source Current
Threshold Voltage
IZCD=5 µA
0.8
0.9
1.0
V
Maximum Delay from ZCD to
Output Turn-On
VCOMP=5 V, fS=60 KHz
100
200
ns
14.0
15.5
17.0
V
1.5
V
V
PFC Zero Current Detection Section
VZCD
tDELAY
tRESTART-PFC
tINHIB
Restart Time
Inhibit Time (Maximum
Switching Frequency Limit)
VCOMP=5 V
V
300
500
700
µs
1.5
2.5
3.5
µs
VZCD-DIS
PFC Enable/Disable Function Threshold Voltage
150
200
250
mV
tZCD-DIS
PFC Enable/Disable Function
Debounce Time
100
150
200
µs
1/2.75
1/3.00
1/3.25
V/V
3
5
7
KΩ
1.2
2.0
mA
VZCD=100 mV
PWM Stage
Feedback Input Section
AV=△VCS /△VFB,
0 VFB-OLP
25.5
34.0
40.0
µs
Continued on the following page…
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
10
VDD=15 V, TA=-40°C ~105°C (TA=TJ), unless otherwise specified.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
16.0
17.5
19.0
V
1.5
V
PWM Output Section
PWM Gate Output Clamping
Voltage
VDD=25 V
VOL
PWM Gate Output Voltage Low
VDD=15 V, IO=100 mA
VOH
PWM Gate Output Voltage High
VDD=15 V, IO=100 mA
tR
PWM Gate Output Rising Time
CL=3 nF,
VDD=12 V, 20~80%
80
110
ns
tF
PWM Gate Output Falling Time
CL=3 nF,
VDD=12 V, 20~80%
40
70
ns
150
200
ns
VCLAMP
8
V
Current Sense Section
tPD
VLIMIT
VSLOPE
Delay to Output
The Limit Voltage on CSPWM
Pin for Over Power
Compensation
Slope Compensation
(4)
tON-BNK
Leading-Edge Blanking Time
VCS-FLOATING
CSPWM Pin Floating VCSPWM
Clamped High Voltage
tCS-H
IDET < 75 µA, TA=25°C
0.81
0.84
0.87
IDET=185 µA, TA=25°C
0.69
0.72
0.75
IDET=350 µA, TA=25°C
0.55
0.58
0.61
IDET=550 µA, TA=25°C
0.37
0.40
0.43
tON=45 µs,
RANGE=Open
0.25
0.30
0.35
tON=0 µs
0.05
0.10
0.15
V
V
300
CSPWM Pin Floating
4.5
Delay Once CSPWM Pin Floating CSPWM Pin Floating
ns
5
V
150
µs
RT Pin Over-Temperature Protection Section
TOTP
TOTP-HYST
IRT
VRT-LATCH
Internal Threshold Temperature
(4)
for OTP
125
Hysteresis Temperature for
(4)
Internal OTP
Latch-Mode Triggering Voltage
Latch-Mode Release Voltage
VRT-OTP-LEVEL
Threshold Voltage for Two-level
Debounce Time
tRT-OTP-H
Debounce Time for OTP
tRT-OTP-L
Debounce Time for Externally
Triggering
155
°C
30
Internal Source Current of RT Pin
VRT-RE-LATCH
140
°C
90
100
110
µA
0.75
0.80
0.85
V
VRT-LATCH
+0.25
V
0.55
V
VRT-LATCH VRT-LATCH
+0.15
+0.20
0.45
0.50
10
VRT VN
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
-25
-10
5
20
35
50
65
80
95
110 125
Temperature(˚C)
Temperature(˚C)
Figure 20. PWM Minimum Off Time for VFB=VG
www.fairchildsemi.com
13
These characteristic graphs are normalized at TA=25°C.
1.0
2.60
2.55
VDET-OVP(V)
VDET-LOW(V)
0.9
0.8
0.7
2.50
2.45
0.6
2.40
0.5
-40
-25
-10
5
20
35
50
65
80
95
-40
110 125
-25
-10
5
35
50
65
80
95
110 125
Figure 22. Reference Voltage for Output
Over-Voltage Protection of DET Pin
Figure 21. Lower Clamp Voltage of DET Pin
110.0
0.90
105.0
0.85
VRT-LATCH(V)
I RT(μA)
20
Temperature(˚C)
Temperature(˚C)
100.0
95.0
0.80
0.75
90.0
0.70
-40
-25
-10
5
20 35 50 65
Temperature(˚C)
80
95
110 125
-40
-10
5
20 35 50 65
Temperature(˚C)
80
95
110 125
Figure 24. Over-Temperature Protection Threshold
Voltage of RT Pin
Figure 23. Internal Source Current of RT Pin
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
-25
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Typical Performance Characteristics (Continued)
www.fairchildsemi.com
14
PFC Stage
Multi-Vector Error Amplifier and THD Optimizer
For better dynamic performance, faster transient
response, and precise clamping on PFC output,
FAN6921AML uses a transconductance type amplifier
with proprietary innovative multi-vector error amplifier.
The schematic diagram of this amplifier is shown in
Figure 25. The PFC output voltage is detected from the
INV pin by an external resistor divider circuit that
consists of R1 and R2. When PFC output variation
voltage reaches 6% over or under the reference voltage
of 2.5 V, the multi-vector error amplifier adjusts its output
sink or source current to increase the loop response to
simplify the compensated circuit.
2.65V
VCOMP
PFC VO
Error
Amplifier
RS
PFC
MOS Filp-Flop
R1
2.5V
3
THD
Optimizer
4
RS
+
INV
R2
+
CSPFC
Sawtooth
Generator
FAN6921
Figure 26. Multi-Vector Error Amplifier with
THD Optimizer
PFC
Vo
IL,AVG (fixed On-Time)
IL,AVG(with THD Optimizer)
2.35V
R1
Co
COMP
2
CCOMP
2.5V
INV
3
Error
Amplifier
Gate Signal
with
THD Optimizer
VCOMP
R2
Sawtooth
Gate Signal
with Fixed
On Time
FAN6921
Figure 25. Multi-Vector Error Amplifier
Figure 27. Operation Waveforms of Fixed On Time
with and without THD Optimizer
The feedback voltage signal on the INV pin is compared
with reference voltage 2.5 V, which makes the error
amplifier source or sink current to charge or discharge
its output capacitor CCOMP. The COMP voltage is
compared with the internally generated sawtooth
waveform to determine the on time of PFC gate.
Normally, with lower feedback loop bandwidth, the
variation of the PFC gate on time should be very small
and almost constant within one input AC cycle.
However, the power factor correction circuit operating at
light-load condition has a defect, zero crossing
distortion, that distorts input current and makes the
system’s Total Harmonic Distortion (THD) worse. To
improve the result of THD at light-load condition,
especially at high input voltage, an innovative THD
optimizer is inserted by sampling the voltage across the
current-sense resistor. This sampling voltage on
current-sense resistor is added into the sawtooth
waveform to modulate the on time of PFC gate, so it is
not constant on time within a half AC cycle. The method
of operation between THD optimizer and PWM is shown
in Figure 26. After THD optimizer processes, around the
valley of AC input voltage, the compensated on time
becomes wider than the original. The PFC on time,
which is around the peak voltage, is narrowed by the
THD optimizer. The timing sequences of the PFC MOS
and the shape of the inductor current are shown in
Figure 27. Figure 28 shows the difference between
calculated fixed on time and fixed on time with THD
optimizer during a half AC cycle.
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
OFF
ON
Input Current
1.8
1.5
Current (A)
1.2
0.9
0.6
PO : 90W
Input Voltage : 90VAC
PFC Inductor : 460mH
CS Resistor : 0.15W
0.3
0
0
0.0014
0.0028
0.0042
0.0056
Time (Seconds)
0.0069
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Functional Description
0.0083
Fixed On-time with THD Optimizer
Fixed On time
Figure 28. Calculated Waveforms of Fixed On Time
with and without THD Optimizer During a Half
AC Cycle
www.fairchildsemi.com
15
VZCD
10V
2.1V
1.75V
RANGE=
Ground
VDS
t
PFCVO
RANGE=
Open
VIN,MAX
VVIN-RANGE-L
VVIN
VVIN-RANGE-H
Figure 29. Hysteresis Behavior between RANGE Pin
and VIN Pin Voltage
Zero Current Detection (ZCD Pin)
Figure 30 shows the internal block of zero-current
detection. The detection function is performed by
sensing the information on an auxiliary winding of the
PFC inductor. Referring to Figure 31, when PFC MOS is
off, the stored energy of the PFC inductor starts to
release to the output load. Then the drain voltage of
PFC MOS starts to decrease since the PFC inductor
resonates with parasitic capacitance. Once the ZCD pin
voltage is lower than the triggering voltage (1.75 V
typical), the PFC gate signal is sent again to start a new
switching cycle.
If PFC operation needs to be shut down due to
abnormal conditions, pull the ZCD pin LOW, with
voltage under 0.2 V (typical), to activate the PFC disable
function to stop PFC switching operation.
For preventing excessive high switching frequency at
light load, a built-in inhibit timer is used to limit the
minimum tOFF time. Even if the ZCD signal has been
detected, the PFC gate signal is not sent during the
inhibit time (2.5 µs typical).
t
PFC
Gate
Inhibit
Time
t
Figure 31. Operation Waveforms of PFC
Zero-Current Detection
Protection for PFC Stage
PFC Output Voltage UVP and OVP (INV Pin)
FAN6921AML provides several kinds of protection for
the PFC stage. PFC output over- and under-voltage are
essential for PFC stage. Both are detected and
determined by INV pin voltage, as shown in Figure 32.
When INV pin voltage is over 2.75 V or under 0.45 V,
due to overshoot or abnormal conditions, and lasts for a
de-bounce time around 70 µs; the OVP or UVP circuit is
activated to stop PFC switching operation immediately.
The INV pin is not only used to receive and regulate
PFC output voltage, but can also perform PFC output
OVP/ UVP protection. For failure-mode test, this pin can
shut down PFC switching if pin floating occurs.
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
RANGE Pin
A built-in low voltage MOSFET can be turned on or off
according to VVIN voltage level. The drain pin of this
internal MOSFET is connected to the RANGE pin.
Figure 29 shows the status curve of VVIN voltage level
and RANGE impedance (open or ground).
0.9V
PFC
Gate
Driver
VO
Debounce
Time
Driver
Q R
VREF (2.5V)
ZCD
0.2V
S
VZ
5
VAC
1.75V
2
Error
Amplifier
Lb
S
Q R
10V
PFC Gate
On
2.1V
FAN6921
1:n
Figure 30. Internal Block of the Zero-Current
Detection
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
Vcomp
COMP
RZCD
INV
Voltage
Detector
CO
3
OVP = (VINV ≥ 2.75V)
UVP = (VINV ≤ 0.45V)
Ccomp
FAN6921
Figure 32. Internal Block of PFC Over- and UnderVoltage Protection
www.fairchildsemi.com
16
AC Input
VCOMP-BO
VCOMP
1.6V
The PFC peak switching current is adjustable by the
current-sense resistor. Figure 33 shows the measured
waveform of PFC gate and CSPFC pin voltage.
VVIN-UVP
VVIN
PFC MOS Current Limit
VVIN-RE-UVP
0V
VINV-BO
2.5V
CSPFC
VINV
1.2V
OPWM
OPFC
OPFC
Brownout
Protection
Debounce
Time 100ms
Figure 33. Cycle-by-Cycle Current Limiting
Brownin/out Protection (VIN Pin)
With AC voltage detection, FAN6921AML can perform
brownin/out protection (AC voltage UVP). Figure 34
shows the key operation waveforms. The VIN pin is
used to detect AC input voltage level and is connected
to AC input by a resistor divider (refer to Figure 1);
therefore, the VVIN voltage is proportional to the AC
input voltage. When the AC voltage drops; and VVIN
voltage is lower than 1 V for 100 ms, the UVP
protection is activated and the COMP pin voltage is
clamped to around 1.6 V. Because PFC gate duty is
determined by comparing the sawtooth waveform and
COMP pin voltage, lower COMP voltage results in
narrow PFC on time, so that the energy converged is
limited and the PFC output voltage decreases. When
INV pin voltage is lower than 1.2 V, FAN6921AML
stops all PFC and PWM switching operation
immediately until VDD voltage drops to turn-off voltage
then rises to turn-on voltage again (UVLO).
When the brownout protection is activated, all switching
operation is turned off, the VDD voltage enters hiccup
mode up and down continuously. Until VVIN voltage is
higher than 1.2 V (typical) and VDD reaches turn-on
voltage again, the PWM and PFC gate is sent out.
Brownout
Protection
Hiccup
Mode
Figure 34. Operation Waveforms of Brownin/out
Protection
VDD
VDD Hiccup Mode
Brownout
Brownin
AC Input
OPWM
OPFC
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
PFC Peak Current Limiting (CSPFC pin)
During PFC stage switching operation, the PFC switch
current is detected by a current-sense resistor on the
CSPFC pin and the detected voltage on this resistor is
delivered to an input terminal of a comparator and
compared with a threshold voltage 0.6 V (typical). Once
the CSPFC pin voltage is higher than the threshold
voltage, PFC gate is turned off immediately.
AC Input
Figure 35. Measured Waveform of Brownin / out
Protection (Adapter Application)
The measured waveforms of brownin/out protection are
shown in Figure 35.
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
17
HV Startup and Operating Current (HV Pin)
The HV pin is connected to the AC line through a
resistor (refer to Figure 1). With a built-in high-voltage
startup circuit, when AC voltage is applied to power
system, FAN6921AML provides a high current to charge
external VDD capacitor to accelerate controller’s startup
time and build up normal rated output voltage within
three seconds. To save power consumption, after VDD
voltage exceeds turn-on voltage and enters normal
operation; this high voltage startup circuit is shut down
to avoid power loss from startup resistor.
Figure 36 shows the characteristic curve of VDD voltage
and operating current IDD. When VDD voltage is lower
than VDD-PWM-OFF, FAN6921AML stops all switching
operation and turns off some unnecessary internal
circuit to reduce operating current. By doing so, the
period from VDD-PWM-OFF to VDD-OFF can be extended and
the hiccup mode frequency can be decreased to reduce
the input power in case of output short circuit. Figure 37
shows the typical waveforms of VDD voltage and gate
signal at hiccup mode operation.
IDD
is detected, FAN6921AML outputs PWM gate signal to
turn on the switch and begin a new switching cycle.
With green mode and valley detection, at light load
condition; power system can perform extended valley
switching at DCM operation and further reduce
switching loss for better conversion efficiency. The FB
pin voltage versus tOFF-MIN time characteristic curve is
shown in Figure 38. As Figure 38 shows, FAN6921AML
can extend tOFF time up to 2.5 ms, which is around
400 Hz switching frequency.
Referring to Figure 1 and Figure 2, FB pin voltage is not
only used to receive secondary feedback signal to
determine gate on time, but also determines PFC stage
on or off status. At no-load or light-load conditions, if PFC
stage is set to be off; that can reduce power consumption
from PFC stage switching device and increase
conversion efficiency. When output loading is decreased,
the FB pin voltage becomes lower and, therefore, the
FAN6921AML can detect the output loading level
according to the FB pin voltage to control the on / off
status of the PFC part.
tOFF-MIN
2.5ms
IDD-OP
PFC On
PFC OFF
37µs
IDD-PWM-OFF
VCTRL-PFC
ΔVCTRL
IDD-ST
8µs
VDD
VFB
VDD-OFF VDD-PWM-OFF VDD-ON
Figure 36. VDD vs. IDD-OP Characteristic Curve
Figure 38.
VDD-ON
VDD-PWM-OFF
IDD-OP
VDD-OFF
Gate
IDD-PWM-OFF IDD-ST
Figure 37. Typical Waveform of VDD Voltage and
Gate Signal in Hiccup Mode Operation
Green-Mode Operation and PFC-ON / OFF Control
(FB Pin)
Green mode is used to further reduce power loss in the
system (e.g. switching loss). It uses an off-time
modulation technique to regulate switching frequency
according to FB pin voltage. When output loading is
decreased, FB voltage becomes lower due to secondary
feedback movement and the tOFF-MIN is extended. After
tOFF-MIN (determined by FB voltage), the internal valley
detection circuit is activated to detect the valley on the
drain voltage of the PWM switch. When the valley signal
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
2.1V(VN)
1.15V(VG)
VFB Voltage vs. tOFF-MIN Time
Characteristic Curve
Valley Detection (DET Pin)
When FAN6921AML operates in green mode, tOFF-MIN is
determined by the green mode circuit according to FB
pin voltage level. After tOFF-MIN, the internal valleydetection circuit is activated. During the off time of the
PWM switch, when transformer inductor current
discharges to zero; the transformer inductor and
parasitic capacitor of PWM switch start to resonate
concurrently. When the drain voltage on the PWM
switch falls, the voltage across on auxiliary winding VAUX
also decreases since auxiliary winding is coupled to
primary winding. Once the VAUX voltage resonates and
falls to negative, VDET voltage is clamped by the DET pin
(refer to Figure 39) and FAN6921AML is forced to flow
out a current IDET. FAN6921AML reflects and compares
this IDET current. If this source current rises to a
threshold current, PWM gate signal is sent out after a
fixed delay time (200 ns typical).
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
PWM Stage
www.fairchildsemi.com
18
DET
10
0.3V
IDET
+
VDET
+
RDET
VAUX
RA
FAN6921
-
Start to
detect valley
The RDET resistor is connected from auxiliary winding to
the DET pin. Engineers can adjust this RDET resistor to
get proper VLIMIT voltage to fit power system needs. The
characteristic curve of IDET current vs. VLIMIT voltage on
CSPWM pin is shown in Figure 42.
I DET VIN N A N P RDET
Figure 39. Valley Detection
VAUX
As the input voltage increases, the reflected voltage on
the auxiliary winding, VAUX, becomes higher (as well as
the current IDET) and the controller regulates the VLIMIT to
a lower level.
IDET flow out
from DET pin
(1)
where VIN is input voltage; NA is turn number of auxiliary
winding; and NP is turn number of primary winding.
VAUX
0V
Delay, then
trigger gate
signal
0V
VDET
VDET
Valley
switching
0V
VAUX= -[VIN•(Na/Np)]
DET pin voltage is clamped
during tON time period
OPWM
tOFF
0V
tON
tOFF
OPWM
Figure 40. Measured Waveform of Valley Detection
Referring to Figure 41, during the on time of the PWM
switch, the input voltage is applied to primary winding
and the voltage across on auxiliary winding, VAUX, is
proportional to primary winding voltage. As the input
voltage increases, the reflected voltage on auxiliary
winding VAUX rises as well. FAN6921AML also clamps
the DET pin voltage and flows out a current IDET. Since
the current, IDET, is in accordance with VAUX,
FAN6921AML can depend on this current IDET during
PWM on time to regulate the current limit level of the
PWM switch to perform high / low line over-power
compensation.
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
Figure 41. Relationship between VAUX and VIN
900
800
700
VLIMIT(mV)
High / Low Line Over-Power Compensation (DET Pin)
Generally, when the power switch turns off, there is a
delay from gate signal falling edge to power switch off.
This delay is produced by an internal propagation delay
of the controller and the turn-off delay of the PWM
switch due to gate resistor and gate-source capacitor
CISS of PWM switch. At different AC input voltage, this
delay time produces different maximum output power
under the same PWM current limit level. Higher input
voltage generates higher maximum output power since
applied voltage on primary winding is higher and causes
higher rising slope inductor current. It results in higher
peak inductor current at the same delay. Furthermore,
under the same output wattage, the peak switching
current at high line is lower than at low line. Therefore,
to make the maximum output power close at different
input voltages, the controller needs to regulate VLIMIT of
the CSPWM pin to control the PWM switch current.
600
500
400
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Auxiliary
Winding
300
0
100
200
300
400
500
600
IDET(µA)
Figure 42. IDET Current vs. VLIMIT Voltage
Characteristic Curve
Leading-Edge Blanking (LEB)
When the PFC or PWM switches are turned on, a
voltage spike is induced on the current-sense resistor
due to the reciprocal effect by reverse recovery energy
of the output diode and COSS of power MOSFET. To
prevent this spike, a leading-edge blanking time is builtin and a small RC filter is recommended between the
CSPWM pin and GND (e.g. 100 Ω, 470 pF).
www.fairchildsemi.com
19
VDD Pin Over-Voltage Protection (OVP)
VDD over-voltage protection is used to prevent device
damage once VDD voltage is higher than device stress
rating voltage. In case of VDD OVP, the controller stops
all switching operation immediately and enters latch-off
mode until the AC plug is removed.
Adjustable Over-Temperature Protection and
Externally Latch Triggering (RT Pin)
Figure 43 is a typical application circuit with an internal
block of RT pin. As shown, a constant current IRT flows
out from the RT pin, so the voltage VRT on RT pin can
be obtained as IRT current multiplied by the resistor,
which consists of NTC resistor and RA resistor. If the RT
pin voltage is lower than 0.8 V and lasts for a debounce
time, latch mode is activated and stops all PFC and
PWM switching.
The RT pin is usually used to achieve over-temperature
protection with a NTC resistor and provides external
latch triggering for additional protection. Engineers can
use an external triggering circuit (e.g. transistor) to pull
low the RT pin and activate controller latch mode.
Generally, the external latch triggering needs to activate
rapidly since it is usually used to protect power system
from abnormal conditions. Therefore, the protection
debounce time of the RT pin is set to around 100 µs
once RT pin voltage is lower than 0.5 V.
For over-temperature protection, because the
temperature would not change immediately; the RT pin
voltage is reduced slowly as well. The debounce time
for adjustable OTP should not need a fast reaction. To
prevent improper latch triggering on the RT pin due to
exacting test conditions (e.g. lightning test); when the
RT pin triggering voltage is higher than 0.5 V, the
protection debounce time is set to around 10 ms. To
avoid improper triggering on the RT pin, it is
recommended to add a small value capacitor (e.g.
1000 pF) paralleled with NTC and RA resistor.
Output Over-Voltage Protection (DET Pin)
Referring to Figure 44, during the discharge time of
PWM transformer inductor; the voltage across on
auxiliary winding is reflected from secondary winding
and therefore the flat voltage on the DET pin is
proportional to the output voltage. FAN6921AML can
sample this flat voltage level after a tOFF blanking time to
perform output over-voltage protection. This tOFF
blanking time is used to ignore the voltage ringing from
leakage inductance of PWM transformer. The sampled
flat voltage level is compared with internal threshold
voltage 2.5 V and, once the protection is activated,
FAN6921AML enters latch mode.
The controller can protect rapidly by this kind of cycleby-cycle sampling method in the case of output over
voltage. The protection voltage level can be determined
by the ratio of external resistor divider RA and RDET. The
flat voltage on DET pin can be expressed by the
following equation:
VDET N A N S VO
(2)
PWM
Gate
VO
VAUX
t
NA
NS
t
PFC _ VO
FAN692 1
Adjustable OverTemperature protection &
External Latch triggering
RA
RDET RA
VDET
VO
NA
NP
NA
RA
N S RDET R A
sampling
here
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Protection for PWM Stage
I RT=100µA
12
NTC
R RT
RT
0.8V
0.5V
Deboun ce
time
tOFF
blanking
Latched
110µs
10ms
0.3V
t
Figure 43. Adjustable Over-Temperature Protection
Figure 44. Operation Waveform of Output
Over-Voltage Detection
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
20
As the output loading is increased, the output voltage is
decreased and the sink current of transistor of optocoupler on primary side is reduced. So the FB pin
voltage is increased by internal voltage bias. In the case
of an open loop, output short circuit, or overload
conditions; this sink current is further reduced and the
FB pin voltage is pulled to high level by internal bias
voltage. When the FB pin voltage is higher than 4.2 V
for 50 ms, the FB pin protection is activated.
Under-Voltage Lockout (UVLO, VDD Pin)
Referring to Figure 36 and Figure 37, the turn-on and
turn-off VDD threshold voltages are fixed at 18 V and
10 V, respectively. During startup, the hold-up capacitor
(VDD capacitor) is charged by the HV startup current
until VDD voltage reaches the turn-on voltage. Before the
output voltage rises to rated voltage and delivers energy
to the VDD capacitor from auxiliary winding, this hold-up
capacitor has to sustain the VDD voltage energy for
operation. When VDD voltage reaches turn-on voltage,
FAN6921AML starts all switching operation if no
protection is triggered before VDD voltage drops to turnoff voltage VDD-PWM-OFF.
VO
FB
Open-Loop
Short-Circuit / Overload
Figure 45. FB Pin Open-Loop, Short Circuit,
and Overload Protections
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Open-Loop, Short-Circuit, and Overload Protection
(FB Pin)
Referring to Figure 45, outside of FAN6921AML; the FB
pin is connected to the collector of transistor of an optocoupler. Inside of FAN6921AML, the FB pin is
connected to an internal voltage bias through a resistor
of ~5 kW.
www.fairchildsemi.com
21
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Flyback PWM Controller
Physical Dimensions
Figure 46. 16-Pin Small Outline Package (SOIC)
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner
without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or
obtain the most recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the
warranty therein, which covers Fairchild products.
Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings:
http://www.fairchildsemi.com/packaging/.
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
22
FAN6921AML — Integrated Critical Mode PFC / Quasi-Resonant Current Mode PWM Controller
© 2011 Fairchild Semiconductor Corporation
FAN6921AML • Rev. 1.0.1
www.fairchildsemi.com
23
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