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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932 DESCRIPTION
The highly integrated SG6932 is designed for power supplies with boost PFC and forward PWM. It requires very few external components to achieve green-mode operation and versatile protections / compensation. It is available in 16-pin DIP and SOP packages. The patented interleave-switching feature synchronizes the PFC and PWM stages and reduces switching noise. At light load, the switching frequency is continuously decreased to reduce power consumption. For PFC stage, the proprietary multi-vector control scheme provides a fast transient response in a low-bandwidth PFC loop, in which the overshoot and undershoot of the PFC voltage are clamped. If the feedback loop is broken, SG6932 shuts off to prevent extra-high voltage on output. For the Forward PWM stage, the synchronized slope compensation ensures the stability of the current loop under continuous-conduction-mode operation. Hiccup operation during output overloading is guaranteed. The soft-start and programmable maximum duty cycle ensure safe operation. SG6932 provides complete protection functions, such as brownout protection and RI open/short latch off.
FEATURES OVERVIEW
Interleaved PFC / PWM switching Green-mode PFC and PWM operation Low operating current Innovative switching-charge multiplier-divider Multi-vector control for improved PFC output transient response Average-current-mode for input-current shaping PFC over-voltage and under-voltage protections PFC and PWM feedback open-loop protection Cycle-by-cycle current limiting for PFC/PWM Slope compensation for PWM Selectable PWM maximum duty cycle 50% and 65% Brownout protection Power-on sequence control and soft-start
APPLICATIONS
Switch-mode power supplies with active PFC Servo system power supplies PC-ATX power supplies
TYPICAL APPLICATION
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
-1-
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932 PIN CONFIGURATION
MARKING DIAGRAMS
T: D=DIP, S=SOP P : Z =Lead Free + ROHS Compatible XXXXXXXX: Wafer Lot Y: Year; WW: Week V: Assembly Location
VRMS RI IEA IPFC IMP ISENSE FBPWM IPWM
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
IAC VEA FBPFC SS VDD OPFC GND OPWM
SG6932TP XXXXXXXXYWWV
ORDERING INFORMATION
Part Number
SG6932DZ SG6932SZ (Preliminary)
Pb-Free
Package
16-pin DIP 16-pin SOP
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
PIN DESCRIPTIONS
Name
VRMS
Pin No. Type
1 Line-Voltage Detection
Function
Line voltage detection. The pin is used for PFC multiplier and brownout protection. Reference setting. One resistor connected between RI and ground determines the switching frequency. A resistor with resistance between 12k ~ 47k is recommended. The switching frequency is equal to [1560 / RI] kHz, where RI is in k. For example, if RI is 24k, the switching frequency is 65kHz.
RI
2
Oscillator Setting
IEA IPFC
3 4
Output of PFC Current This is the output of the PFC current amplifier. The signal from this pin is compared with an Amplifier internal sawtooth and determines the pulse width for PFC gate drive. Inverting Input of PFC The inverting input of the PFC current amplifier. Proper external compensation circuits Current Amplifier result in excellent input power factor via average-current-mode control. Non-inverting Input of The non-inverting input of the PFC current amplifier and the output of the multiplier. Proper PFC Current Amplifier external compensation circuits result in excellent input power factor via average current and Output of mode control. Multiplier Peak Current Limit Setting for PFC The peak current limit setting for PFC.
IMP
5
ISENSE
6
FBPWM
7
The control input for voltage-loop feedback of PWM stage. It is internally pulled high through PWM Feedback Input a 6.5k resistance. Usually an external opto-coupler from secondary feedback circuit is connected to this pin. PWM Current Sense PWM Gate Drive Ground PFC Gate Drive Supply The current sense input for the PWM stage. Via a current sense resistor, this pin provides the control input for peak-current-mode control and cycle-by-cycle current limiting. The totem pole output drive for PWM MOSFET. This pin is internally clamped under 18V to protect the MOSFET. The power ground. The totem pole output drive for the PFC MOSFET. This pin is internally clamped under 18V to protect the MOSFET. The power supply pin. The threshold voltages for start-up and turn-off are 14V and 10V, respectively. The operating current is lower than 10mA. During start-up, the SS pin charges an external capacitor with a 50A constant current source. The voltage on FBPWM is clamped by SS during start-up. In the event of a protection condition occurring and/or PWM being disabled, the SS pin is quickly discharged. The voltage of SS pin can be used to select 50% or 65% maximum duty cycle. The feedback input for PFC voltage loop. The inverting input of PFC error amplifier. This pin is connected to the PFC output through a divider network.
IPWM OPWM GND OPFC VDD
8 9 10 11 12
SS
13
PWM Soft-Start
FBPFC
14
Voltage Feedback Input for PFC
VEA
15
Error Amplifier Output The error amplifier output for PFC voltage feedback loop. A compensation network (usually for PFC Voltage a capacitor) is connected between this pin and ground. A large capacitor value results in a Feedback Loop narrow bandwidth and improves the power factor. Input AC Current For normal operation, this input is used to provide current reference for the multiplier. The suggested maximum IAC is 360A.
IAC
16
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
BLOCK DIAGRAM
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
-4-
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
ABSOLUTE MAXIMUM RATINGS
Symbol
VDD IAC VHigh VLow PD TJ Tstg RjC TL ESD
Parameter
DC Supply Voltage* Input AC Current OPWM, OPFC, IAC Others Power Dissipation Operating Junction Temperature Storage Temperature Range Thermal resistance (Junction-to-Case) Lead Temperature (Wave soldering, 10 seconds) Electrostatic Discharge Capability, Human Body Model Electrostatic Discharge Capability, Machine Model
Test Conditions Value
25 2 -0.5 to 25V At TA<50 -0.5 to 7V 0.8 -40 to 125 -55 to +150 DIP SOP 260 4.5 250 33.64 41.95
Unit
V mA V V W
/W
KV V
*All voltage values, except differential voltages, are given with respect to the network ground terminal.
RECOMMENDED OPERATING JUNCTION TEMPERATURE: -30C~ 85C*
* For proper operation.
ELECTRICAL CHARACTERISTICS
VDD=15V, TA=25C unless otherwise noted.
VDD Section
Symbol VDD-OP
IDD ST IDD-OP VTH-ON VDD-min VDD-OVP TVDD-OVP
Parameter Continuously Operating Voltage
Start-Up Current Operating Current Start Threshold Voltage Min. Operating Voltage VDD OVP1 (turn off PWM with delay) Delay time of VDD OVP1
Test Conditions
VDD -0.16V VDD=15V; OPFC OPWM open
Min.
Typ.
10 6
Max. 20
20 10 15 11 25.5 25
Unit V
A mA V V V s
13 9 23.5 RI=24k 8
14 10 24.5
Oscillator & Green-Mode Operation
Symbol
VRI FOSC FOSC-MINFREQ RI RIOPEN RISHORT
Parameter
RI Voltage PWM Frequency Minimum Frequency in Green Mode RI Range RI Pin Open Protection If RI > RIopen , PWM Turned Off RI Pin Short Protection If RI< RIshort , PWM Turned Off
Test Conditions
RI=24k RI=24k
Min.
1.176 62 18 12
Typ.
1.200 65 20
Max.
1.224 68 22 47
Unit
V KHz KHz k k k
200 2
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
VRMS for UVP and ON/OFF
Symbol
VRMS-UVP-1
Parameter
RMS AC Voltage Under-Voltage Threshold to Turn Off PFC (with TUVP Delay) for UVP Mode1
Test Conditions
Min.
0.75
Typ.
0.8
Max.
0.85
Unit
V
VRMS-UVP-2
Recovery Level on VRMS for UVP Under-Voltage Protection Propagation to
VRMS-UVP-1+ VRMS-UVP-1+ VRMS-UVP-1+ 0.17V RI=24k 150 0.19V 195 0.21V 240
V
TUVP
Turn Off PFC Delay Time (No Delay for Start-up)
ms
PFC Stage Voltage Error Amplifier
Symbol
VREF Av Zo OVPFBPFC
Parameter
Reference Voltage Open-Loop Gain Output Impedance PFC Over-voltage Protection PFC Feedback Voltage Protection Hysteresis Clamp-High Feedback Voltage Clamp-High Gain Clamp-Low Feedback Voltage Clamp-Low Gain Maximum Source Current Maximum Sink Current PFC Feedback Under-Voltage Protection Output High Voltage on VEA Voltage level on FBPFC to Enable OPWM During Start-up Debounce Time of PFC UVP
Test Conditions
Min.
2.95
Typ.
3.00 60 110
Max.
3.05
Unit
V dB k
3.20 60 3.10 2.75 1.5 70 0.35 6 2.6 40
3.25 90 3.15 0.5 2.85 6.5 2.0 110 0.40 7 2.7 70
3.30 120 3.20 2.90
V mV V mA/V V mA/mV mA A
OVPFBPFC
VFBPFC-H GFBPFC-H VFBPFC-L GFBPFC-L IFBPFC-L. IFBPFC-H. UVPVFB VFBHIGH VRD-FBPFC TUVP-PFC
0.45 8 2.8 120
V V V s
Current Error Amplifier
Symbol
VOFFSET AI BW CMRR VOUT-HIGH VOUT-LOW IMR1, IMR2 IL IH
Parameter
Input Offset Voltage ((-) > (+)) Open-loop Gain Unit Gain Bandwidth Common-mode Rejection Ratio Output High Voltage Output Low Voltage Reference Current Source Maximum Source Current Maximum Sink Current
Test Conditions
Min.
Typ.
8 60 1.5
Max.
Unit
mV dB MHz dB V
VCM=0 ~ 1.5V 3.2
70 0.2
V A mA mA
RI=24k (IMR=20+IRI*0.8)
50 3 0.25
70
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
Peak Current Limit
Symbol
IP Vpk TpkD Bnkt
Parameter
Constant Current Output Peak Current Limit Threshold Voltage Cycle-by-Cycle Limit (Vsense < Vpk) Propagation Delay Leading-Edge Blanking Time
Test Conditions
RI=24k VRMS=1.05V VRMS=3V
Min.
90 0.15 0.35 270
Typ.
100 0.20 0.40 350
Max.
110 0.25 0.45 200 450
Unit
A V V ns ns
Multiplier
Symbol
IAC IMO-max IMO-1 IMO-2 VIMP
Parameter
Input AC Current Maximum Multiplier Current Output; Multiplier Current Output (Low-Line, High-Power) Multiplier Current Output (High-Line, High-Power) Voltage of IMP Open
Test Conditions
Multiplier Linear Range RI=24k VRMS=1.05V; IAC=90A; VEA=7.5V; RI=24k VRMS=3V; IAC=264A; VEA=7.5V; RI=24k
Min.
0
Typ.
230
Max.
360
Unit
A A
200 65 3.4
230 85 3.9
280
A A
4.4
V
PFC Output Driver
Symbol
VZ-PFC VOL-PFC VOH-PFC TR-PFC Tf-PFC DC(MAX)
Parameter
Output Voltage Maximum (Clamp) Output Voltage Low Output Voltage High Rising Time Falling Time Maximum Duty Cycle
Test Conditions
VDD=20V VDD=15V; IO=100mA VDD=13V; IO=100mA VDD=15V; CL=5nF; O/P=2V to 9V VDD=15V; CL=5nF; O/P=9V to 2V
Min.
Typ.
16
Max.
18 1.5
Unit
V V V ns ns %
8 40 40 93 70 60 120 110 97
PWM Stage FBPWM
Symbol
AV ZFB FBOPEN-LOOP TOPEN-PWM-Hiccup TOPEN-PWM VN SG VG
Parameter
FB to Current Comparator Attenuation Input Impedance PWM Open-Loop Protection Voltage Interval of PWM Open-Loop Protection Reset PWM Open-Loop Protection Delay Time Frequency Reduction Threshold on FBPWM Green-Mode Modulation Slope Voltage on FBPWM for Minimum Green-Mode Frequency
Test Conditions
Min.
2.2 4 4.2
Typ.
2.7 5 4.5 600 95 2.1 75 1.60
Max. Unit
3.2 7 4.8 700 120 2.3 90 1.75 V/V k V ms ms V Hz/mV V
RI=24k RI=24k
500 80 1.9 60 1.35
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
PWM-Current Sense
Symbol
TPD-PWM VLIMIT TBNK-PWM
Parameter
Propagation Delay to Output - VLIMIT Loop Peak Current Limit Threshold Voltage Leading-Edge Blanking Time Slope Compensation Vs=VSLOPE x (Ton/T) Vs: Compensation Voltage Added to Current Sense
Test Conditions
VDD=15V, OPWM drops to 9V
Min.
60 0.65 270
Typ.
0.70 350
Max.
120 0.75 450
Unit
ns V ns
VSLOPE
0.40
0.45
0.55
V
Output Driver
Symbol
VZ-PWM TPWM VOL-PWM VOH-PWM TR-PWM TF-PWM
Parameter
Output Voltage Maximum (Clamp) Interval of OPWM Lags Behind OPFC at Start-up Output Voltage Low Output Voltage High Rising Time Falling Time
Test Conditions
VDD=20V RI=24k VDD=15V; IO=100mA VDD=13V; IO=100mA VDD=15V; CL=5nF; O/P=2V to 9V VDD=15V; CL=5nF; O/P=9V to 2V
Min.
2
Typ.
16 4
Max.
18 6 1.5
Unit
V ms V V ns ns
8 30 30 60 50 120 110
Maximum Duty Cycle
Symbol
DC SS=6V DC SS=5V
Parameter
Maximum Duty Cycle for SS=6V Maximum Duty Cycle for SS=5V
Test Conditions
RI=24k RI=24k
Min.
62 46
Typ.
Max.
66 50
Unit
% %
Soft-Start
Symbol
ISS VDC-MAX-50% VDC-MAX--65% RD
Parameter
Constant Current Output for Soft-Start Voltage of SS for 50% Maximum Duty Cycle Voltage of SS for 65% Maximum Duty Cycle Discharge Resistance
Test Conditions
RT=24k
Min.
44 6
Typ.
50
Max.
56 5
Unit
A V V
470
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
TYPICAL CHARACTERISTICS
Start-Up Current (IDD ST) vs Temperature
Min. Operation Voltge (VDD-MIN) vs Temperature
20.0 18.0 16.0 14.0
IDD ST (uA)
11.0 10.8 10.6 10.4
VTH-MIN(V)
-40 -25 -10 5 20 35 50 65 80 95 110 125
12.0 10.0 8.0 6.0 4.0 2.0 0.0
Temperature ()
10.2 10.0 9.8 9.6 9.4 9.2 9.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature ()
Start Threshold Voltage (VTH-ON) vs Temperature
Frequency vs. FB Voltage
15.0 14.8 14.6
Frequency (KHz)
70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0
1.3 -40 -25 -10 5 20 35 50 65 80 95 110 125 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6
14.4
VTH-ON(V)
14.2 14.0 13.8 13.6 13.4 13.2 13.0
Temperature ()
FB Voltage (V)
Start-up Current vs. VDD Voltage
Duty Cycle vs. FB Voltage
70.0
10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
60.0 50.0
Duty Cycle (%)
VDD Voltage (V)
Start-up Current (uA)
40.0 30.0 20.0 10.0 0.0
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2
FB Voltage (V)
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Product Specification Green-Mode PFC / Forward PWM Controller
VDD OVP Threshold (VDD-OVP) vs Temperature
SG6932
PFC over Voltage Protection (OVPPFC) vs Temperature
25.5 25.3 25.1
VDD-OVP (V)
3.30 3.29 3.28 3.27
OVPPFC (V)
24.9 24.7 24.5 24.3 24.1 23.9 23.7 23.5
-40 -25 -10 5 20 35 50 65 80 95 110 125
3.26 3.25 3.24 3.23 3.22 3.21 3.20
-40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature ()
Temperature ()
PWM Frequency (FOSC) vs Temperature
Rising Time (TR-PFC) vs Temperature
68.0 67.5 67.0 66.5 66.0 65.5 65.0 64.5 64.0 63.5 63.0 62.5 62.0
-40 -25 -10 5 20 35 50 65 80 95 110 125 Temperature ()
100.0 90.0 80.0
TR(nS)
FOSC (KHz)
70.0 60.0 50.0 40.0 30.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature ()
PWM Frequency (FOSC-GREEN) vs Temperature
Falling Time (TF-PFC) vs Temperature
22.0 21.5
FOSC-MINFREQ (KHz)
100.0 90.0 80.0
TF (nS)
-40 -25 -10 5 20 35 50 65 80 95 110 125
21.0 20.5 20.0 19.5 19.0 18.5 18.0
Temperature ()
70.0 60.0 50.0 40.0 30.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature ()
Reference Voltage (VREF) vs Temperature
Maximum Duty Cycle (SS=5V) vs Temperature
3.05 3.04 3.03 3.02
DCMAX (%)
-40 -25 -10 5 20 35 50 65 80 95 110 125
50.0 49.5 49.0 48.5 48.0 47.5 47.0 46.5 46.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
VREF (V)
3.01 3.00 2.99 2.98 2.97 2.96 2.95
Temperature ()
Temperature ()
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
Maximum Duty Cycle (SS=6V) vs Temperature
SG6932
Rising Time (TR-PWM) vs Temperature
66.0 65.5 65.0
DCMAX (%)
120.0 110.0 100.0
TR-PWM (nS)
-40 -25 -10 5 20 35 50 65 80 95 110 125
64.5 64.0 63.5 63.0 62.5 62.0
Temperature ()
90.0 80.0 70.0 60.0 50.0 40.0 30.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature ()
PWM Open Loop Protection voltage (FBOPEN-LOOP) vs Temperature
Fall Time (TF-PWM) vs Temperature
4.80 4.75 4.70 4.65 4.60 4.55 4.50 4.45 4.40 4.35 4.30 4.25 4.20
-40 -25 -10 5 20 35 50 65 80 95 110 125
110.0 100.0 90.0
TF-PWM (nS)
FBOPEN-LOOP (V)
80.0 70.0 60.0 50.0 40.0 30.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature ()
Temperature ()
PWM Open Loop Protection Delay Time (TOPEN-PWM) vs Temperature
Constant Current Output for Soft Start (ISS) vs Temperature
120 115
TOPEN-PWM (mS)
55 54 53 52
ISS (uA)
-40 -25 -10 5 20 35 50 65 80 95 110 125
110 105 100 95 90 85 80
Temperature ()
51 50 49 48 47 46 45
-40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature ()
Peak Current Limit Threshold Voltge (VLIMIT) vs Temperature
0.75 0.74 0.73 0.72
VLIMIT (V)
0.71 0.70 0.69 0.68 0.67 0.66 0.65
-40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature ()
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
OPERATION DESCRIPTION
The highly integrated SG6932 is designed for power supplies with boost PFC and forward PWM. It requires very few external components to achieve green-mode operation and versatile protections / compensation. The patented interleave-switching feature synchronizes the PFC and PWM stages and reduces switching noise. At light load, the switching frequency is linearly decreased to reduce power consumption. The PFC function is implemented by averagecurrent-mode control. The patented switching charge multiplier-divider provides high-degree noise immunity for the PFC circuit. This also enables the PFC circuit to operate over a much wider region. The proprietary multi-vector output voltage control scheme provides a fast transient response in a low-bandwidth PFC loop, in which the overshoot and undershoot of the PFC voltage are clamped. If the feedback loop is broken, the SG6932 shuts off PFC to prevent extra-high voltage on output. For the forward PWM, the synchronized slope compensation ensures the stability of the current loop under continuous-mode operation. Hiccup operation during output overloading is also guaranteed. To prevent the power supply from drawing large current during start-up, the start-up for PWM stage is delayed 4ms after the PFC output voltage reaches its setting value. In addition, SG6932 provides complete protection functions such as brownout protection and built-in latch for over-voltage and RI open/short.
Figure 1. Input Voltage Detection
Switching Frequency / Current Sources
The switching frequency of SG6932 can be programmed by the resistor RI connected between RI pin and GND. The relationship is:
fPWM =
1560 (kHz ) ------------RI (k)
(1)
For example, a 24k resistor RI results in a 65kHz switching frequency. Accordingly, constant current IT flows through RI.
I
T
=
1.2V RI (k )
(mA) ----------------
(2)
IT is used to generate internal current reference.
IAC signal
Figure 1 shows the IAC pin connected to input voltage by a resistance and the current, IAC, is the input for PFC multiplier. For the linear range of IAC 0~360A, the range input voltage should be connected a resistance over 1.2M.
Line Voltage Detection (VRMS)
Figure 2 shows a resistive divider with low-pass filtering for line-voltage detection on VRMS pin. The VRMS voltage is used for the PFC multiplier and brownout protection. For brownout protection, when the VRMS voltage drops below 0.8V, OPFC turns off.
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
Figure 4. Control Loop of PFC Stage Figure 2. Line-Voltage Detection on VRMS Pin The current source output from the switching charge multiplier-divider can be expressed as:
Interleave Switching / Green-Mode
The SG6932 uses interleaved switching to synchronize the PFC and PWM stages. This reduces switching noise and spreads the EMI emissions. Figure 3 shows off-time (TOFF) inserted between the turn-off of the PFC gate drives and the turn-on of the PWM. The off-time (TOFF) is increased in response to the decreasing of the voltage level of FBPWM; therefore, the PWM switching frequency is linearly decreased to reduce switching losses.
IMO = K x
IAC x VEA (A ) VRMS 2
(3)
IMP, the current output from IMP pin, is the summation of IMO and IMR1. IMR1 and IMR2 are identical fixed-current sources. R2 and R3 are also identical. They are used to pull high the operating point of the IMP and IPFC pins when the voltage across RS goes negative with respect to ground. Through the differential amplification of the signal across RS, better noise immunity is achieved. The output of IEA is compared with an internal sawtooth and the pulse width for PFC is determined. Through the average current-mode control loop, the input current IS is proportional to IMO:
OPFC
OPWM TOFF
IMO x R 2 = IS x RS
(4)
Figure 3. Interleaved Switching According to Equation 4, the minimum value of R2 and maximum of RS can be determined since IMO should not exceed the specified maximum value. There are different concerns in determining the value of the sense resistor, RS. The value of RS should be small enough to reduce power consumption, but large enough to maintain the resolution. A current transformer (CT) may be used to improve the efficiency of high power converters. To achieve good power factor, the voltage for VRMS and VEA should be kept as DC as possible, according to Equation 3. Good RC filtering for VRMS and narrow bandwidth (lower than the line frequency) for voltage loop are suggested for better input current shaping. The www.sg.com.tw * www.fairchildsemi.com September 19, 2007
PFC Operation
The purpose of a boost active power factor corrector (PFC) is to shape the input current of a power supply. The input current waveform and phase follow that of the input voltage. Using SG6932, average-current-mode control is utilized for continuous-current-mode operation for the PFC booster. With the innovative multi-vector control for voltage loop and switching-charge multiplier-divider for current reference, excellent input power factor is achieved with good noise immunity and transient response. Figure 4 shows the total control loop for the average-current-mode control circuit of SG6932. (c) System General Corp. Version 1.1.1 (IAO33.0011.B2) - 13 -
Product Specification Green-Mode PFC / Forward PWM Controller transconductance error amplifier has output impedance RO (>90k) and a capacitor CEA (1F ~ 10F) connected to ground (as shown in Figure 5). This establishes a dominant pole f1 for the voltage loop:
SG6932
3.15V
+
SG69XX
f1 =
1 2 x R0 x CEA
2.85V
(5)
RA
FBPFC
3V
The average total input power can be expressed as:
+
RB
K
IACxVEA
VRMS
2
Pin = Vin( rms ) x Iin( rms ) VRMS x I MO VRMS x I AC x VEA 2 VRMS
CEA
VEA
(6) Figure 5. Multi-Vector Error Amplifier
Vin x VEA RAC VRMS x VEA 2 VRMS
From Equation 6, VEA, the output of the voltage error amplifier, actually controls the total input power and the power delivered to the load.
Cycle-by-Cycle Current Limiting
SG6932 provides cycle-by-cycle current limiting for both PFC and PWM stages. Figure 6 shows the peak current limit for the PFC stage. The PFC gate drive is terminated once the voltage on the ISENSE pin goes below VPK. The voltage of VRMS determines the voltage of VPK. The relationship between VPK and VRMS is shown in Figure 6. The amplitude of the constant current, IP, is determined by the internal current reference, IT, according to the equation:
Multi-Vector Error Amplifier
The voltage-loop error amplifier is transconductance, which has high output impedance (> 90k). A capacitor CEA (1F ~ 10F) connected from VEA to ground provides a dominant pole for the voltage loop. Although the PFC stage has a low bandwidth voltage loop for better input power factor, the innovative multi-vector error amplifier provides a fast transient response to clamp the overshoot and undershoot of the PFC output voltage. Figure 5 shows the block diagram of the multi-vector error amplifier. When the variation of the feedback voltage exceeds 5% of the reference voltage, the transconductance error amplifier adjusts its output impedance to increase the loop response. If RA is opened, SG6932 shuts off immediately to prevent extra-high voltage on the output capacitor.
Ip = 2 x I
T
= 2x
1.2V R I
(7)
Therefore, the peak current of the IS is given by (VRMS<1.05V):
IS_peak =
(Ip x RP) - 0.2V RS
(8)
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
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www.sg.com.tw * www.fairchildsemi.com September 19, 2007
Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
0.55V
FBPWM
+
+ IPWM
0.7V
SG69XX
Figure 6. Current Limit Figure 8. Slope Compensation
Power-On Sequence / Soft-Start
The SG6932 is enabled whenever the line voltage is higher than the brownout threshold. Once the SG6932 is active, the PFC stage is enabled first. The PWM stage is enabled following a 4ms delay after FBPFC voltage exceeds 2.7V. During start-up of PWM stage, the SS pin charges an external capacitor with a constant-current source. The voltage on FBPWM is clamped by SS during start-up. In the event of a protection condition occurring and/or PWM being disabled, the SS pin is quickly discharged.
Limited Power Control
Every time the output of power supply is shorted or over loaded, the FBPWM voltage increases. If the FB voltage is higher than a designed threshold, 4.2V, for longer than 95ms, the PWM output is turned off.
Gate Drivers
SG6932 output stages are fast totem-pole gate drivers. The output driver is clamped by an internal 18V Zener diode to protect the power MOSFET.
3V 2.7V
FBPFC
Protections
The SG6932 provides full protection functions to prevent the power supply and the load from being damaged. The protection features include:
4mS
OPFC
OPWM
Figure 7. Power-On Sequence
PFC Feedback Over-Voltage Protection. When the PFC feedback voltage exceeds the over-voltage threshold, the SG6932 inhibits the PFC switching signal. This protection also prevents the PFC power converter from operating abnormally while the FBPFC pin is open. Second PFC Over-Voltage Protection (OVP_PFC). The PFC stage over-voltage input. The comparator disables the PFC output driver if this input exceeds 3.25V. This pin can be connected to the FBPFC pin or the PFC boost output through a divider network. This pin provides an extra input for PFC over-voltage protection. PFC Feedback Under-Voltage Protection. The SG6932 stops the PFC switching signal whenever the PFC feedback voltage drops below the under-voltage threshold. This protection feature is designed to prevent the PFC
Forward PWM and Slope Compensation
The PWM stage is designed for forward power converters. Peak current mode control is used to optimize system performance. Slope compensation is added to stabilize the current loop. The SG6932 inserts a synchronized positively sloped ramp at each switching cycle. The positively sloped ramp is represented by the voltage signal Vs-comp. In the example in Figure 8, the ramp signal voltage is 0.55V.
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
- 15 -
www.sg.com.tw * www.fairchildsemi.com September 19, 2007
Product Specification Green-Mode PFC / Forward PWM Controller power converter from experiencing abnormal conditions while the FBPFC pin is shorted to ground. VDD Over-Voltage Protection. The PFC and PWM stages are disabled whenever the VDD voltage exceeds the over-voltage threshold. RI Pin Open / Short Protection. The RI pin is used to set the switching frequency and internal current reference. The PFC and PWM stages of SG6932 are disabled whenever the RI pin is short or open.
SG6932
independently tied from the decoupling capacitor to the PFC output capacitor CO. The ground in the output capacitor CO is the major ground reference for power switching. To provide a good ground reference and reduce the switching noise of both the PFC and PWM stages, the ground traces 6 and 7 should be located very near and be low impedance. The IPFC pin is connected directly to RS through R3 to improve noise immunity. Do not incorrectly connect to the ground trace 2. The IMP and ISENSE pins should be connected directly via the resistors R2 and RP to another terminal of RS.
PCB Layout
SG6932 has a single ground pin, which prevents high sink currents in the output being returned separately. Good high-frequency or RF layout practices should be followed. Avoid long PCB traces and component leads. Locate decoupling capacitors near the SG6932. A resistor of 5 ~ 20 is recommended, connected in series from the output to the gate of the MOSFET. Isolating the interference between the PFC and PWM stages is also important. Figure 9 shows an example of the PCB layout. The ground trace 1 is connected from the ground pin of SG6932 to the decoupling capacitor, which should be low impedance and as short as possible. The ground trace 2 provides a signal ground. It should be connected directly to the decoupling capacitor CDD and/or to the ground pin of the SG6932. The ground trace 3 is
Figure 9. PCB Layout
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
- 16 -
www.sg.com.tw * www.fairchildsemi.com September 19, 2007
Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
REFERENCE CIRCUIT
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
- 17 -
www.sg.com.tw * www.fairchildsemi.com September 19, 2007
Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
PACKAGE INFORMATION 16 PINS - PLASTIC DIP (D)
D
16 9
E1
1 8
E
eB
A2 L e b1 A1
A
DIMENSION
Symbol A A1 A2 b b1 D E E1 e L eB Millimeter Min. 0.381 3.175 Inch Min. 0.015 0.125
Typ.
Max. 5.334 3.429
Typ.
Max. 0.210 0.135
18.669 6.121 2.921 8.509 0
3.302 1.524 0.457 19.177 7.620 6.299 2.540 3.302 9.017 7
19.685 6.477 3.810 9.525 15
0.735 0.241 0.115 0.335 0
0.130 0.060 0.018 0.755 0.300 0.248 0.100 0.130 0.355 7
0.775 0.255 0.150 0.375 15
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
- 18 -
www.sg.com.tw * www.fairchildsemi.com September 19, 2007
Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
16 PINS - PLASTIC SOP (S)
16 9
E
H
Detail A
1
b e
8
F
c
D A2 y A1 A
L Detail A
DIMENSION
Symbol A A1 A2 b c D E e H L F y Millimeter Min. 1.346 0.101 1.244 Inch Min. 0.053 0.004 0.049
Typ.
Max. 1.753 0.254 1.499
Typ.
Max. 0.069 0.010 0.059
0.406 0.203 9.804 3.810 1.270 5.791 0.406 0.381X45 0 0.101 8 0 6.198 1.270 0.228 0.016 10.008 3.988 0.386 0.150
0.016 0.008 0.394 0.157 0.050 0.244 0.050 0.015X45 0.004 8
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
- 19 -
www.sg.com.tw * www.fairchildsemi.com September 19, 2007
Product Specification Green-Mode PFC / Forward PWM Controller
SG6932
(c) System General Corp. Version 1.1.1 (IAO33.0011.B2)
- 20 -
www.sg.com.tw * www.fairchildsemi.com September 19, 2007

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