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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
achieve versatile protections. It is available in a 20-pin SOP package. The patented interleave-switching feature synchronizes the PFC and PWM stages and reduces switching noise. 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, the SG6905 will shut off PFC to prevent extra-high voltage on output. For the flyback PWM, the synchronized slope compensation ensures the stability of the current loop under continuous-conduction-mode operation. Built-in line-voltage compensation maintains constant output-power limit. Hiccup operation during output overloading is also guaranteed. During start-up, the RDY pin will be pulled low until the PFC output voltage reaches to the setting level. This signal can be used to control the second power stage for proper power on sequence. SG6905 provides complete protection functions such as brownout protection and RI pin open/short.
FEATURES
Interleaved PFC/PWM switching Green mode PWM operation Low start-up and operating current Innovative switching charge multiplier-divider Multi-vector control for improved PFC output transient response Average-current-mode control for PFC PFC over-voltage and under-voltage protections PFC remote on/off Control PFC and PWM feedback open-loop protection Cycle-by-cycle current limiting for PFC/PWM Slope compensation for PWM Constant power limit for PWM Power-on sequence control Brownout protection Over temperature protection
APPLICATIONS
Switching Power Suppliers with Active PFC High-Power Adaptors
DESCRIPTION
The highly integrated SG6905 is specially designed for power supplies with boost PFC and flyback PWM. It requires very few external components to
TYPICAL APPLICATION
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905 PIN CONFIGURATION
MARKING DIAGRAMS
T: S = SOP P : Z =Lead Free Null=regular package XXXXXXXX: Wafer Lot Y: Year; WW: Week V: Assembly Location
SG6905TP XXXXXXXXYWWV
ORDERING INFORMATION
Part Number
SG6905SZ
Pb-Free
Package
20-pin SOP
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
PIN DESCRIPTIONS
Name
VRMS
Pin No. Type
1 Line-Voltage Detection
Function
Line voltage detection. The pin is used for PFC multiplier, brownout protection .For brownout protection; the controller will be disabled after a delay time when the VRMS voltage drops below a threshold voltage. Reference setting. One resistor connected between RI and ground determines the switching frequency. The switching frequency is equal to [1560 / RI] kHz, where RI is in k. For example, if RI is equal to 24k, then the switching frequency will be 65 kHz. This pin supplies an over temperature protection signal. A constant current is output from this pin. An external NTC thermistor must be connected from this pin to ground. The impedance of the NTC thermistor decreases whenever the temperature increases. Once the voltage of the OTP pin drops below the OTP threshold, the SG6905 will be disabled. This is the output of the PFC current amplifier. The signal from this pin will be compared with an internal saw-tooth and hence determine the pulse width for PFC gate drive. The inverting input of the PFC current amplifier. Proper external compensation circuits will result in excellent input power factor via average-current-mode control. The non-inverting input of the PFC current amplifier and also the output of multiplier. Proper external compensation circuits will result in excellent input power factor via average- current- mode control. The peak-current setting for PFC. The control input for voltage-loop feedback of PWM stage. It is internally pulled high through a 6.5k resistance. Usually an external opto-coupler from secondary feedback circuit is connected to this pin. The current-sense input for the Flyback PWM. Via a current sense resistor, this pin provides the control input for peak-current-mode control and cycle-by-cycle current limiting. Signal Ground During startup, the SS pin will charge an external capacitor with a 50A (RI=24k) constant current source. The voltage on FBPWM will be clamped by SS during startup. In the event of a protection condition occurring and/or PWM being disabled, the SS pin will be quickly discharged. The totem-pole output drive for the Flyback PWM MOSFET. This pin is internally clamped under 17V to protect the MOSFET. Power Ground The totem-pole output drive for the PFC MOSFET. This pin is internally clamped under 17V to protect the MOSFET. The power supply pin. This pin outputs a ready signal to control the power on sequence. Once the SG6905 is turned on and the FBPFC(PFC Feedback input)voltage is higher than 2.7V, will lock this pin to high impedance. Disable the SG6905 Will reset this pin to the low. The PFC stage will disabled whenever the voltage at this pin is exceed 2.45V. The feedback input for PFC voltage loop. The inverting input of PFC error amp. This pin is connected to the PFC output through a divider network. capacitor) is connected between this pin and ground. A large capacitor value will result in a narrow bandwidth and hence improve the power factor. Before start-up, this input is used to provide startup current for VDD. For normal operation, this input is used to provide current reference for the multiplier.
RI
2
Oscillator Setting
OTP
3
Over Temperature Protection Output for PFC Current Amplifier Inverting Input for PFC Current Amplifier Non-inverting Input
IEA
4
IPFC
5
IMP
6
for PFC Current Amplifier Peak Current Limit Setting for PFC PWM Feedback Input
ISENSE
7
FBPWM
8
IPWM AGND SS
9 10 11
PWM Current Sense Ground PWM Soft Start
OPWM GND OPFC VDD RDY PFC_ON FBPFC
12 13 14 15 16 17 18
PWM Gate Drive Ground PFC Gate Drive Supply Ready signal output Remote On/Off Voltage Feedback Input for PFC PFC voltage feedback loop
Error-Amp Output for The error-amp output for PFC voltage feedback loop. A compensation network (usually a VEA 19
IAC
20
Input AC Current
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
BLOCK DIAGRAM
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
ABSOLUTE MAXIMUM RATINGS
Symbol
VVDD IAC VHigh VLow PD TJ TSTG Rj-C TL VESD,HBM
Parameter
DC Supply Voltage* Input AC Current OPWM, OPFC, IAC Others Power Dissipation At TA < 50C Operating Junction Temperature Storage Temperature Range Thermal resistance (Junction to Case) Lead Temperature (Wave soldering or IR, 10 seconds) ESD capability, HBM model
Value
25 2 -0.3 to +25 -0.3 to +7 0.8 -40 to +125 -55 to +150 23.64 260 4.5
Unit
V mA V V W C C C/W C KV V
VESD,MM ESD capability, Machine model 250 *All voltage values, except differential voltages, are given with respect to GND pin. *Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device.
RECOMMENDED OPERATING CONDITIONS
Symbol
TA
Parameter
Operating Ambient Temperature*
Value
-20 to +85
Unit
C
*For proper operation
ELECTRICAL CHARACTERISTICS (VDD=15V, TA=25C UNLESS NOTED) VDD section
Symbol
VDD-OP IDD-ST IDD-OP VDD-ON VDD-OFF VDD-OVP tD-VDDOVP VDD-TH-G
Parameter
Continuously Operating Voltage Start-up Current Operating Current Start Threshold Voltage Min. Operating Voltage VDD OVP Threshold Debounce Time of VDD OVP VDD Low-Threshold Voltage to Exit Green-OFF Mode
Test Conditions
VDD-ON-0.16V VDD= 15V; RI= 24K OPFC, OPWM open
Min.
Typ.
10 6
Max.
20 25 10 17 11 25.5 25 VDD-OFF +2.1
Unit
V A mA V V V s V
15 9 23.5 RI= 24K 8 VDD-OFF +0.9
16 10 24.5 VDD-OFF +1.5
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
VRMS for UVP
Symbol
VRMS-UVP-1 VRMS-UVP-2 tD-PWM tUVP
Parameter
RMS AC Voltage Under Voltage Protection Threshold (with TUVP delay) Recovery level on VRMS When UVP occurs, the interval from OPFC off to OPWM off Under Voltage Protection Delay Time (No delay for startup)
Test Conditions
Min.
0.75 VRMS-UVP1 +0.17
Typ.
0.8 VRMS-UVP1+0.19
Max.
0.85 VRMS-UVP1
Unit
V V ms ms
+0.21
RI= 24K RI= 24K
tUVP-Min +9 150 195
tUVP-Min +14 240
PFC stage Voltage Error Amplifier
Symbol
VREF Av Zo OVPFBPFC OVPPFC tOVP-PFC VFBPFC-H GFBPFC-H VFBPFC-L GFBPFC-L IFBPFC-L IFBPFC-H UVPFBPFC tUVP-PFC
Parameter
Reference Voltage Open-loop Gain Output Impedance PFC Over-Voltage-Protection on FBPFC PFC Feedback Voltage Protection Hysteresis Debounce Time of PFC OVP 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 Debounce Time of PFC UVP
Test Conditions
Min.
2.95
Typ.
3 60 110
Max.
3.05
Unit
V dB K
3.2 60 RI= 24K 40 3.1 2.75 1.5 70 0.35 RI= 24K 40
3.25 90 70 3.15 0.5 2.85 6.5 2 110 0.4 70
3.3 120 120 3.2 2.9
V mV s V A/mV V mA/mV mA A
0.45 120
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= 24 K (IMR=20+IRI*0.8)
50 3 0.25
70
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
Peak Current Limit
Symbol
IP VPK tPD-PFC tLEB-PFC
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 70
Typ.
100 0.2 0.4 120
Max.
110 0.25 0.45 200 170
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= 24 K VRMS= 3V; IAC= 264A; VEA= 7.5V;RI= 24 K
Min.
0
Typ.
250
Max.
360
Unit
A A
200 65 3.4
250 85 3.9
280
A A
4.4
V
PFC Oscillator
Symbol
FOSC FDV FDT
Parameter
PFC Frequency Frequency Variation versus VDD Deviation Frequency Variation versus Temp. Deviation
Test Conditions
RI= 24K VDD= 11 to 20V TA= -20 to 85C
Min.
62
Typ.
65
Max.
68 2 2
Unit
KHz % %
PFC Output Driver
Symbol
VZ VOL-PFC tPFC VOH-PFC tR-PFC tF-PFC DCYMAX
Parameter
Output Voltage Maximum (Clamp) Output Voltage Low The interval of OPFC lags behind OPWM at startup Output Voltage High Rising Time Falling Time Maximum Duty Cycle
Test Conditions
VDD= 20V VDD= 15V; IO= 100mA
Min.
Typ.
16
Max.
18 1.5 13.5
Unit
V V ms V
8 VDD= 13V; IO= 100mA VDD= 15V; CL= 5nF; O/P= 2V to 9V VDD= 15V;CL= 5nF; O/P= 9V to 2V 93 40 8 40
11
70 60
120 110 98
ns ns %
PFC On/Off
Symbol
ION/OFF VOFF tPFC_ON
Parameter
Constant Current Output for PFC_ON pin Turn-off Threshold Voltage Debounce Time of PFC_On/Off
Test Conditions
RI= 24K RI= 24K
Min.
44 2 40
Typ.
50 2.45 70
Max.
56 2.9 120
Unit
A V s
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
PWM Stage FBPWM
Symbol
Av-PWM ZFB IFB FBOPEN-LOOP tOPEN-PWM tOFF-PWM-DLY VFB-N SG VFB-G
Parameter
FB to Current Comparator Attenuation Input Impedance Maximum Source Current PWM Open Loop Protection voltage PWM Open Loop Protection Delay Time PWM off to turn on delay time Frequency Reduction Threshold on FBPWM Green-Mode Modulation Slope Voltage on FBPWM at Fs = FOSC-MINFREQ
Test Conditions
Min.
2.5 4 0.8 4.2
Typ.
3.1 5 1.2 4.5 56 600 2.0 100 1.6
Max.
3.5 7 1.5 4.8 70 750 2.2 120 1.75
Unit
V/V K mA V ms ms V Hz/V V
RI= 24K PFC_ON > VOFF PFC_ON > VOFF PFC_ON > VOFF
45 450 1.8 80 1.35
PWM-Current Sense
Symbol
tPD-PWM VLIMIT tLEB-PWM
Parameter
Propagation Delay to Output 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
Min.
50 0.85 170
Typ.
0.9 250
Max.
120 0.95 350
Unit
ns V ns
VSLOPE
0.3
0.33
0.36
V
PWM Oscillator
Symbol
FOSC FOSC-MIN FDV FDT
Parameter
PWM Frequency Minimum Frequency Frequency Variation versus VDD Deviation Frequency Variation versus Temp. Deviation
Test Conditions
RI= 24K RI= 24K; FBPWM= VFB-G; PFC_ON > VOFF VDD= 11V to 20V TA= -20 to 85C
Min.
62 19
Typ.
65 21
Max.
68 23.5 2 2
Unit
KHz KHz % %
PWM Output Driver
Symbol
VZ-PWM VOL-PWM VOH-PWM tR-PWM tF-PWM DCYMAXPWM
Parameter
Output Voltage Maximum (Clamp) Output Voltage Low Output Voltage High Rising Time Falling Time PWM 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
8 30 30 73 60 50 78 120 110 83
ns ns %
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
RDY section
Symbol
VFB-RDY-HIGH IFB-RDY-HIGH VOL tRDY
Parameter
Threshold voltage of FBPFC for RDY high impedance The leakage current of RDY is a high impedance at the voltage of FBPFC Output Voltage Low for RDY is failed The interval between FBPFC exceeds VFB-RDY-HIGH and RDY is high impedance
Test Conditions
Min.
2.65
Typ.
2.7
Max.
2.75 10 0.5
Unit
V A V ms
FBPFC= 2V ISINK= 1mA 4
6
OTP section
Symbol
IOTP VOTP-ON VOTP-OFF tOTP
Parameter
OTP Pin Output Current Recovery level on OTP OTP Threshold Voltage OTP Debounce Time
Test Conditions
RI= 24K
Min.
90 1.35 1.15
Typ.
100 1.4 1.2
Max.
110 1.45 1.25 25
Unit
A V V s
RI= 24K
8
Soft-Start Section
Symbol
ISS RD
Parameter
Constant Current Output for Soft Start Discharge RDSON
Test Conditions
RT= 24K
Min.
44
Typ.
50 470
Max.
56
Unit
A
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
TYPICAL CHARACTERISTICS
S tart-Up Current (ID D - S T ) vs Temperature
25 20
11.0 10.5 10.0 9.5 9.0 8.5
Minimum Operating V oltage (V D D - O F F ) vs Temperature
I D D - S T (uA)
10 5 0 -40 -25 -10 5 20 35 50 65 80 95 110 125
V D D - O F F (V)
15
8.0 -40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature (
)
Temperature (
)
Operating Current (ID D - O P ) vs Temperature
10.0 8.8 68 67
PWM Fre que ncy (F OSC ) vs Te m pe ra ture
ID D - O P (mA)
66 7.6 6.4 5.2 4.0 -40 -25 -10 5 20 35 50 65 80 95 110 125
F OSC (KH z)
65 64 63 62 -40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature (
)
Te m pe ra ture (
)
Start Threshold Voltage (V D D - O N ) vs Temperature
17.0 16.5
V D D Ove r Volta ge Prote ction (V D D - OVP ) vs
25.5
Te m pe ra ture
V D D - O N (V )
15.5 15.0 14.5 14.0 -40 -25 -10 5 20 35 50 65 80 95 110 125
V D D - OVP (V)
16.0
25.0
24.5
24.0
23.5 -40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature (
)
Te m pe ra ture (
)
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
P FC Over V oltage P rotection on FBP FC (OV P F BP F C ) vs Temperature
3.30
104 120
Rising Time (t R - P F C ) vs Temperature
3.28
OVP F BPF C (V)
t R - P F C (ns)
-40 -25 -10 5 20 35 50 65 80 95 110 125
3.26 3.24 3.22 3.20
88 72 56 40 -40 -25 -10 5 20 35 50 65 80 95 110 125
Te m pe ra ture (
)
Temperature (
)
T hreshold Voltage of F BPF C for R DY high impedance
2.75 2.73
Falling Time (t F - P F C ) vs Temperature
110 96
( V F B - R D Y -H I GH ) vs T emperature
V F B- R D Y- H IG H (V)
t F - P F C (ns)
2.71 2.69 2.67 2.65 -40 -25 -10 5 20 35 50 65 80 95 110 125
82 68 54 40 -40 -25 -10 5 20 35 50 65 80 95 110 125
Te m pe ra ture (
)
Temperature (
)
Reference V oltage (V R E F ) vs Temperature
3.05 3.03 3.01 2.99 2.97 2.95 -40 -25 -10 5 20 35 50 65 80 95 110 125
Ma xim um D uty C ycle (D C Y M AX ) vs Te m pe ra ture
98 97
D C Y M AX (% )
V R E F (V )
96 95 94 93 -40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature (
)
Te m pe ra ture (
)
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Product Specification Green mode PFC/Flyback-PWM Controller
P WM Open Loop P rotection V oltage (FB O P E N - LO O P ) vs Temperature
4.80 4.68 4.56 4.44 4.32 4.20 -40 -25 -10 5 20 35 50 65 80 95 110 125
750 690 630 570 510 450 -40 -25 -10 5 20 35 50 65 80 95 110 125
SG6905
PWM off to turn on delay time (tO FF-P WM-DLY ) vs Temperature
FB O P E N - LO O P (V )
Temperature (
)
tO FF-P WM-DLY (ms)
Temperature (
)
PWM Opem Loop Protection Delay Time (tO P E N-P WM ) vs Temperature
70
Rising Time (t R - P W M ) vs Temperature
120 102
65
tO P E N-P WM (ms)
t R - P W M (ns)
60 55 50 45 -40 -25 -10 5 20 35 50 65 80 95 110 125
84 66 48 30 -40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature (
)
Temperature (
)
P eak Current Limit Threshold V oltage (V LIM IT ) vs
0.95 0.93
Falling Time (t F - P W M ) vs Temperature
110 94
Temperature
t F - P W M (ns)
-40 -25 -10 5 20 35 50 65 80 95 110 125
V LI M I T (V )
0.91 0.89 0.87 0.85
78 62 46 30 -40 -25 -10 5 20 35 50 65 80 95 110 125
Temperature (
)
Temperature (
)
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Product Specification Green mode PFC/Flyback-PWM Controller
PWM Ma xim um D uty C ycle (D C Y M AXPW M ) vs
83 81
SG6905
OTP Threshold V oltage (V O T P - O F F ) vs Temperature
1.25 1.23
Te m pe ra ture
D C Y M AXPW M (% )
79 77 75 73 -40 -25 -10 5 20 35 50 65 80 95 110 125
V O T P- O F F (V)
1.21 1.19 1.17 1.15 -40 -25 -10 5 20 35 50 65 80 95 110 125
Te m pe ra ture (
)
Te m pe ra ture (
)
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
OPERATION DESCRIPTION
The highly integrated SG6905 is specially designed for power supplies consist of boost PFC and flyback PWM. It requires very few external components to achieve green-mode operation and versatile protections. It is available in 20-pin SOP package. The patented interleave-switching feature synchronizes the PFC and PWM stages and reduces switching noise. At light loads, 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, the SG6905 will shut off PFC to prevent extra-high voltage on output. For the flyback PWM, the synchronized slope compensation ensures the stability of the current loop under continuous-conduction-mode operation. Built-in line-voltage compensation maintains constant output-power limit. Hiccup operation during output overloading is also guaranteed. During start-up, the RDY pin will be pulled low until the PFC output voltage reaches to the setting level. This signal can be used to control the second power stage for proper power on sequence. SG6905 provides complete protection functions such as brownout protection and RI pin open/short.
FIG.1 Start up circuit of the SG6905
PFC ON/OFF Control and RDY Signal for Power ON Sequence Control
A PFC on/off control function is built-in to control the power on and power off of PFC controller. Once the voltage on this pin is pulled below 2.45V, the OPFC will be enabled. Once the OPFC is enabled, the output voltage of the PFC converter will gradually increase to the regulated voltage. To provide a proper power on sequence control, a RDY pin will be pulled high after the PFC voltage reach 90% (FBPFC>VFB-RDY-HIGH) of its regulated voltage.
Switching Frequency and Current Start Up
Figure 1 shows the start up circuit of the SG6905. A resistor RAC is utilized to charge VDD capacitor through S1. The turn-on and turn-off threshold of SG6905 are fixed internally at 16V/10V. During start-up, the hold-up capacitor must be charged to 16V through the start-up resistor so that SG6905 will be enabled. The hold-up capacitor will continue to supply VDD before the energy can be delivered from auxiliary winding of the main transformer flyback converter. VDD must not drop below 10V during this start-up process. This UVLO hysteresis window ensures that hold-up capacitor is adequate to supply VDD during start-up. Since SG6905 consumes less than 25A startup current, the value of RAC can be large to reduce power consumption. One 10uF capacitor should hold enough energy for successful start-up. After start-up, S1 will switch so that the current IAC will be the input for PFC multiplier. This helps reduce circuit complexity and power consumption. (c) System General Corp. Version 1.1.1 (IAO33.0060.B1)
Sources
The switching frequency of SG6905 can be programmed by the resistor RI connected between RI pin and GND. The relationship is:
FOSC =
1560 RI (k )
(kHz) ----------- (1)
For example, a 24K resistor RI results in a 65 KHz switching frequency. Accordingly, a constant Current IT will flow through RI.
IT =
1.2V RI (k )
(mA) ---------------- (2)
IT is used to generate internal current reference.
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Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
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, the SG6905 is disabled with 195ms delay time if the voltage VRMS drops below 0.8V. For PFC multiplier, please refer to below section for more details. FIG.2 Line voltage detection circuit Refer to Fig. 3, the current output from IMP pin, IMP, is the summation of IMO and IMR1. IMR1 and IMR2 are identical fixed current sources. They are used to pull high the operating point of the IMP and IPFC pins since the voltage across RS goes negative with respect to ground. The constant current sources IMR1 and IMR2 are typically 60A. Through the differential amplification of the signal across Rs, better noise immunity is achieved. The output of IEA will be compared with an internal sawtooth and hence the pulse width for PFC is determined. Through the average current-mode control loop, the input current Is will be proportional to IMO.
Interleave Switching
The SG6905 uses interleaved switching to synchronize the PFC and Flyback stages. This reduces switching noise and spreads the EMI emissions. Figure 3 shows that an off-time TOFF is inserted in between the turn-off of the PFC gate drive and the turn-on of the PWM.
IMO x R2 = IS x RS -------------------FIG.3 Interleaved switching pattern
(4)
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 to reduce power consumption, but it should be 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 constant 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 trans-conductance error amplifier has output impedance ZO and a capacitor CEA (1F ~ 10F) should be connected to ground. This establishes a dominant pole f1 for the voltage loop.
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 will follow that of the input voltage. Using SG6905, 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 SG6905. The current source output from the switching charge multiplier/divider can be expressed as:
I MO = K x
IAC x V EA V RMS
2
(uA) ------------
(3)
f1 =
1 2 x ZO x CEA
----------------------
(5)
(c) System General Corp. Version 1.1.1 (IAO33.0060.B1)
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www.sg.com.t w * www.fairchildsemi.com September 27, 2007
Product Specification Green mode PFC/Flyback-PWM Controller The average total input power can be expressed as:
SG6905
From Equation 6, VEA, the output of the voltage error amplifier, actually controls the total input power and hence the power delivered to the load.
Pin = Vin(rms) x Iin(rms) VRMS x I MO VRMS x I AC x VEA 2 VRMS
---------------- (6)
Vin x VEA R AC VRMS x 2 VRMS = 2x VEA R AC
FIG.4 Average current mode control loop
(c) System General Corp. Version 1.1.1 (IAO33.0060.B1)
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www.sg.com.t w * www.fairchildsemi.com September 27, 2007
Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
Multi-vector Error Amplifier
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 trans-conductance error amplifier will adjust its output impedance to increase the loop response. Either RA or RB is opened, OPFC of SG6905 will shut off immediately to prevent extra-high voltage on the output capacitor.
FIG. 6 VRMS controlled current limiting The peak current of the ISENSE is given by (VRMS<1.05V):
ISENSE_peak =
(IP x RP) - 0.2V -----------------RS
(8)
Flyback PWM and Slope Compensation
As shown in Figure 7, peak-current-mode control is utilized for Flyback PWM. The SG6905 inserts a synchronized 0.5V ramp at the beginning of each switching cycle. This built-in slope compensation ensures stable operation for continuous current-mode operation.
FIG. 5 Multi-vector error amplifier FIG. 7 Peak current control loop
Cycle-by-Cycle Current Limiting
SG6905 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 ISENSE pin goes below VPK. The voltage of VRMS determines the voltage of VPK. The relationship between VPK and VRMS is also shown in Figure 6. The amplitude of the constant current IP is determined by the internal current reference according to the following equation:
When the IPWM voltage, across the sense resistor, reaches the threshold voltage (0.9V), the OPWM will be turned off after a small propagation delay tPD-PWM. To improve stability or prevent sub-harmonic oscillation, a synchronized positive-going ramp in inserted at every switching cycle.
IP = 2 x
1.2V --------------------RI
(7)
(c) System General Corp. Version 1.1.1 (IAO33.0060.B1)
- 17 -
www.sg.com.t w * www.fairchildsemi.com September 27, 2007
Product Specification Green mode PFC/Flyback-PWM Controller
SG6905 Soft-Start
During startup of PWM stage, the SS pin will charge an external capacitor with a constant current source. The voltage on FBPWM will be clamped by SS voltage during startup. In the event of a protected condition occurring and/or PWM being disabled, the SS pin will be quickly discharged.
Limited Power Control
Every time when the output of power supply is shorted or over loaded, the FBPWM voltage will increase. If the FBPWM voltage is higher than a designed threshold, FBOPEN-LOOP (4.5V), for longer than tOPEN-PWM (56ms), the OPWM will then be turned off. As OPWM is turned off, the supply voltage VDD will also begin decreasing. When VDD is lower than the turn-off threshold, VDD-OFF (10V), SG6905 will be totally shut down. Due to the start up resistor, VDD will be charged up to the turn-on threshold voltage, VDD-ON (16V), until SG6905 is enabled again. If the over loading condition still exists, the protection will take place repeatedly. This will prevent the power supply from being overheated under over loading condition.
Gate Drivers
SG6905 output stage is a fast totem-pole gate driver. The output driver is clamped by an internal 18V Zener diode to protect the external power MOSFET.
Over-Temperature Protection (OTP)
SG6905 provides an OTP pin for over-temperature protection. A constant current is output from this pin. If RI is equal to 24K, then the magnitude of the constant current will be 100A. An external NTC thermistor must be connected from this pin to ground shown as Figure 8. When the OTP voltage drops below VOTP-OFF (1.2V), SG6905 will be disabled, and will not recovery until OTP voltage exceeds VOTP-ON (1.4V).
Fig. 8 OTP function
(c) System General Corp. Version 1.1.1 (IAO33.0060.B1)
- 18 -
www.sg.com.t w * www.fairchildsemi.com September 27, 2007
Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
PACKAGE INFORMATION 20 PINS - PLASTIC SOP (S)
E
H
Detail A
1
b
10 e
F
c
A D
c
y
A2 A1
L Detail A
Dimension:
Symbol
A A1 A2 b c D E e H L F y
Millimeter Min. Typ.
2.362 0.101 2.260 0.406 0.203 12.598 7.391 1.270 10.007 0.406 0.508X45 0
Max.
2.642 0.305 2.337
Inch Min.
0.093 0.004 0.089
Typ.
Max.
0.104 0.012 0.092
0.016 0.008 12.903 7.595 10.643 1.270 0.101 8 0.496 0.291 0.050 0.394 0.016 0.020X45 0 0.004 8 0.419 0.050 0.508 0.299
(c) System General Corp. Version 1.1.1 (IAO33.0060.B1)
- 19 -
www.sg.com.t w * www.fairchildsemi.com September 27, 2007
Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
20 PINS - PLASTIC SSOP (R)
20
11
E
1
10 "A"
b
e 0.004
GAUGE PLANE
A2 L L1
c
A1 SEATING PLANE
DETAIL : A
Dimension:
Symbol
A A1 A2 b C D E E1 e L L1
Millimeter Min.
1.346 0.102 0.203 0.178 8.560 5.791 3.810 0.406 0
Inch Typ. Max.
1.752 0.254 1.499 0.305 0.254 8.738 6.198 3.988 1.270 8
Min.
0.053 0.004 0.008 0.007 0.337 0.228 0.150 0.016 0
Typ.
0.064 0.006
Max.
0.069 0.010 0.059 0.012 0.010 0.344 0.244 0.157 0.050 8
8.661 5.994 3.912 0.635 BASIC 0.635 1.041 BASIC
0.341 0.236 0.154 0.025 BASIC 0.025 0.041 BASIC
(c) System General Corp. Version 1.1.1 (IAO33.0060.B1)
- 20 -
www.sg.com.t w * www.fairchildsemi.com September 27, 2007
A
-H-
E1
Product Specification Green mode PFC/Flyback-PWM Controller
SG6905
(c) System General Corp. Version 1.1.1 (IAO33.0060.B1)
- 21 -
www.sg.com.t w * www.fairchildsemi.com September 27, 2007

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