FAIRCHILD SG6905SZ

Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
achieve versatile protections. It is available in a 20-pin
SOP package.
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
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.
APPLICATIONS
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.
Switching Power Suppliers with Active PFC
High-Power Adaptors
SG6905 provides complete protection functions such as
brownout protection and RI pin open/short.
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
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
-1-
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
MARKING DIAGRAMS
SG6905TP
XXXXXXXXYWWV
PIN CONFIGURATION
T: S = SOP
P : Z =Lead Free
Null=regular package
XXXXXXXX: Wafer Lot
Y: Year; WW: Week
V: Assembly Location
ORDERING INFORMATION
Part Number
Pb-Free
SG6905SZ
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
Package
20-pin SOP
-2-
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
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
RI
2
Oscillator Setting
switching frequency. The switching frequency is equal to [1560 / RI] kHz, where RI is in
Over Temperature
Protection
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.
Output for PFC
This is the output of the PFC current amplifier. The signal from this pin will be compared
Current Amplifier
with an internal saw-tooth and hence determine the pulse width for PFC gate drive.
kΩ. For example, if RI is equal to 24kΩ, then the switching frequency will be 65 kHz.
OTP
3
IEA
4
Inverting Input for
IPFC
5
PFC Current
Amplifier
IMP
6
ISENSE
7
FBPWM
8
The inverting input of the PFC current amplifier. Proper external compensation circuits will
result in excellent input power factor via average-current-mode control.
Non-inverting Input
The non-inverting input of the PFC current amplifier and also the output of multiplier.
for PFC Current
Proper external compensation circuits will result in excellent input power factor via
Amplifier
average- current- mode control.
Peak Current Limit
Setting for PFC
PWM Feedback
Input
The peak-current setting for PFC.
The control input for voltage-loop feedback of PWM stage. It is internally pulled high
through a 6.5kΩ 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
IPWM
9
PWM Current Sense
provides the control input for peak-current-mode control and cycle-by-cycle current
AGND
10
Ground
Signal Ground
SS
11
PWM Soft Start
During startup, the SS pin will charge an external capacitor with a 50µA (RI=24kΩ)
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.
OPWM
12
PWM Gate Drive
GND
13
Ground
OPFC
14
PFC Gate Drive
VDD
15
Supply
RDY
16
Ready signal output
turned on and the FBPFC(PFC Feedback input)voltage is higher than 2.7V, will lock this
PFC_ON
17
Remote On/Off
The PFC stage will disabled whenever the voltage at this pin is exceed 2.45V.
FBPFC
18
Voltage Feedback
The feedback input for PFC voltage loop. The inverting input of PFC error amp. This pin is
Input for PFC
connected to the PFC output through a divider network.
limiting.
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
pin to high impedance. Disable the SG6905 Will reset this pin to the low.
Error-Amp Output for The error-amp output for PFC voltage feedback loop. A compensation network (usually a
VEA
IAC
19
20
PFC voltage
capacitor) is connected between this pin and ground. A large capacitor value will result in
feedback loop
a narrow bandwidth and hence improve the power factor.
Input AC Current
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
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.
-3-
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
BLOCK DIAGRAM
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
-4-
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Value
Unit
VVDD
DC Supply Voltage*
25
V
IAC
Input AC Current
2
mA
VHigh
OPWM, OPFC, IAC
-0.3 to +25
V
VLow
Others
-0.3 to +7
V
PD
Power Dissipation At TA < 50°C
0.8
W
TJ
Operating Junction Temperature
-40 to +125
°C
TSTG
Storage Temperature Range
-55 to +150
°C
Rθj-C
Thermal resistance (Junction to Case)
23.64
°C/W
TL
Lead Temperature (Wave soldering or IR, 10 seconds)
260
°C
VESD,HBM
ESD capability, HBM model
4.5
KV
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.
V
RECOMMENDED OPERATING CONDITIONS
Symbol
Parameter
Value
Unit
TA
Operating Ambient Temperature*
-20 to +85
°C
*For proper operation
ELECTRICAL CHARACTERISTICS (VDD=15V, TA=25°C UNLESS NOTED)
VDD section
Symbol
Parameter
VDD-OP
Continuously Operating Voltage
Test Conditions
Min.
Typ.
Max.
Unit
20
V
IDD-ST
Start-up Current
VDD-ON-0.16V
10
25
µA
IDD-OP
Operating Current
VDD= 15V; RI= 24KΩ
6
10
mA
VDD-ON
Start Threshold Voltage
15
16
17
V
VDD-OFF
Min. Operating Voltage
9
10
11
V
VDD-OVP
VDD OVP Threshold
23.5
24.5
25.5
V
tD-VDDOVP
Debounce Time of VDD OVP
25
µs
VDD-TH-G
VDD Low-Threshold Voltage to Exit
VDD-OFF
VDD-OFF
VDD-OFF
V
Green-OFF Mode
+0.9
+1.5
+2.1
OPFC, OPWM open
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
RI= 24KΩ
-5-
8
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
VRMS for UVP
Symbol
VRMS-UVP-1
VRMS-UVP-2
tD-PWM
tUVP
Parameter
Test Conditions
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)
RI= 24KΩ
Min.
Typ.
Max.
Unit
0.75
0.8
0.85
V
VRMS-UVP-
VRMS-UVP-
VRMS-UVP-
1 +0.17
1+0.19
1
+0.21
tUVP-Min
tUVP-Min
+9
+14
V
ms
RI= 24KΩ
150
195
240
ms
Test Conditions
Min.
Typ.
Max.
Unit
2.95
3
3.05
PFC stage
Voltage Error Amplifier
Symbol
Parameter
VREF
Reference Voltage
Av
Open-loop Gain
Zo
Output Impedance
OVPFBPFC
PFC Over-Voltage-Protection on FBPFC
OVPPFC
tOVP-PFC
60
110
3.2
PFC Feedback Voltage Protection Hysteresis
Debounce Time of PFC OVP
RI= 24KΩ
3.25
V
dB
KΩ
3.3
V
60
90
120
mV
40
70
120
µs
3.1
3.15
3.2
V
2.9
V
VFBPFC-H
Clamp-High Feedback Voltage
GFBPFC-H
Clamp-High Gain
VFBPFC-L
Clamp-Low Feedback Voltage
GFBPFC-L
Clamp-Low Gain
IFBPFC-L
Maximum Source Current
IFBPFC-H
Maximum Sink Current
70
110
UVPFBPFC
PFC Feedback Under Voltage Protection
0.35
0.4
0.45
V
tUVP-PFC
Debounce Time of PFC UVP
RI= 24KΩ
40
70
120
µs
Test Conditions
Min.
Typ.
Max.
Unit
0.5
µA/mV
2.75
2.85
6.5
mA/mV
1.5
2
mA
µA
Current Error Amplifier
Symbol
Parameter
VOFFSET
Input Offset Voltage ((-) > (+))
8
mV
AI
Open-loop Gain
60
dB
BW
Unit Gain Bandwidth
1.5
MHz
CMRR
Common-mode Rejection Ratio
VOUT-HIGH
Output High Voltage
VOUT-LOW
Output Low Voltage
IMR1, IMR2
Reference Current Source
IL
Maximum Source Current
IH
Maximum Sink Current
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
VCM= 0~1.5V
70
dB
3.2
V
0.2
RI= 24 KΩ (IMR=20+IRI*0.8)
50
70
3
µA
mA
0.25
-6-
V
mA
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
Peak Current Limit
Symbol
IP
VPK
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
Constant Current Output
RI= 24KΩ
90
100
110
µA
Peak Current Limit Threshold Voltage
VRMS= 1.05V
0.15
0.2
0.25
V
Cycle-by-Cycle Limit (VSENSE < VPK)
VRMS= 3V
0.35
0.4
0.45
V
tPD-PFC
Propagation Delay
tLEB-PFC
Leading Edge Blanking Time
200
ns
70
120
170
ns
Typ.
Max.
Unit
Multiplier
Symbol
Parameter
Test Conditions
Min.
IAC
Input AC Current
Multiplier Linear Range
0
IMO–max
Maximum Multiplier Current Output;
RI= 24KΩ
Multiplier Current Output
VRMS= 1.05V; IAC= 90µA;
(low-line, high-power)
VEA= 7.5V;RI= 24 KΩ
Multiplier Current Output
VRMS= 3V; IAC= 264µA;
(high-line, high-power)
VEA= 7.5V;RI= 24 KΩ
IMO-1
IMO–2
VIMP
Voltage of IMP Open
360
250
200
250
65
85
3.4
3.9
µA
µA
280
µA
µA
4.4
V
PFC Oscillator
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
FOSC
PFC Frequency
RI= 24KΩ
62
65
68
KHz
FDV
Frequency Variation versus VDD Deviation
VDD= 11 to 20V
2
%
FDT
Frequency Variation versus Temp. Deviation
TA= -20 to 85°C
2
%
Typ.
Max.
Unit
16
18
V
1.5
V
11
13.5
ms
PFC Output Driver
Symbol
Parameter
Test Conditions
VZ
Output Voltage Maximum (Clamp)
VDD= 20V
VOL-PFC
Output Voltage Low
VDD= 15V; IO= 100mA
tPFC
The interval of OPFC lags behind OPWM at
Min.
8
startup
VOH-PFC
Output Voltage High
VDD= 13V; IO= 100mA
8
tR-PFC
Rising Time
VDD= 15V; CL= 5nF;
40
70
120
V
ns
40
60
110
ns
98
%
Unit
O/P= 2V to 9V
tF-PFC
Falling Time
VDD= 15V;CL= 5nF;
O/P= 9V to 2V
DCYMAX
Maximum Duty Cycle
93
PFC On/Off
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
ION/OFF
Constant Current Output for PFC_ON pin
RI= 24KΩ
44
50
56
µA
VOFF
Turn-off Threshold Voltage
2
2.45
2.9
V
tPFC_ON
Debounce Time of PFC_On/Off
40
70
120
µs
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
RI= 24KΩ
-7-
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
PWM Stage
FBPWM
Symbol
Parameter
Min.
Typ.
Max.
Av-PWM
FB to Current Comparator Attenuation
Test Conditions
2.5
3.1
3.5
Unit
V/V
ZFB
Input Impedance
4
5
7
KΩ
IFB
Maximum Source Current
0.8
1.2
1.5
mA
FBOPEN-LOOP
PWM Open Loop Protection voltage
4.2
4.5
4.8
V
45
56
70
ms
450
600
750
ms
PFC_ON > VOFF
1.8
2.0
2.2
V
Green-Mode Modulation Slope
PFC_ON > VOFF
80
100
120
Hz/V
Voltage on FBPWM at Fs = FOSC-MINFREQ
PFC_ON > VOFF
1.35
1.6
1.75
V
Test Conditions
Min.
Typ.
Max.
Unit
tOPEN-PWM
PWM Open Loop Protection Delay Time
tOFF-PWM-DLY
PWM off to turn on delay time
VFB-N
Frequency Reduction Threshold on FBPWM
SG
VFB-G
RI= 24KΩ
PWM-Current Sense
Symbol
Parameter
tPD-PWM
Propagation Delay to Output
50
VLIMIT
Peak Current Limit Threshold Voltage
0.85
Leading-Edge Blanking Time
tLEB-PWM
120
ns
0.9
0.95
V
170
250
350
ns
0.3
0.33
0.36
V
Slope Compensation
VSLOPE
VS = VSLOPE x (Ton/T)
VS : Compensation Voltage Added to
Current Sense
PWM Oscillator
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
FOSC
PWM Frequency
RI= 24KΩ
62
65
68
KHz
19
21
23.5
KHz
RI= 24KΩ; FBPWM= VFB-G;
FOSC-MIN
Minimum Frequency
FDV
Frequency Variation versus VDD Deviation
VDD= 11V to 20V
2
%
FDT
Frequency Variation versus Temp. Deviation
TA= -20 to 85°C
2
%
PFC_ON > VOFF
PWM Output Driver
Symbol
Parameter
Test Conditions
VZ-PWM
Output Voltage Maximum (Clamp)
VDD= 20V
VOL-PWM
Output Voltage Low
VDD= 15V; IO= 100mA
VOH-PWM
Output Voltage High
tR-PWM
Rising Time
tF-PWM
Falling Time
DCYMAXPWM
PWM Maximum Duty Cycle
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
VDD= 13V; IO= 100mA
VDD= 15V; CL= 5nF;
O/P= 2V to 9V
VDD= 15V; CL= 5nF;
O/P= 9V to 2V
-8-
Min.
Typ.
Max.
16
18
V
1.5
V
8
Unit
V
30
60
120
ns
30
50
110
ns
73
78
83
%
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
RDY section
Symbol
Parameter
VFB-RDY-HIGH
Threshold voltage of FBPFC for RDY high
impedance
IFB-RDY-HIGH
The leakage current of RDY is a high
impedance at the voltage of FBPFC
VOL
Output Voltage Low for RDY is failed
tRDY
The interval between FBPFC exceeds
VFB-RDY-HIGH and RDY is high impedance
Test Conditions
Min.
Typ.
Max.
Unit
2.65
2.7
2.75
V
FBPFC= 2V
10
µA
ISINK= 1mA
0.5
V
6
ms
4
OTP section
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
IOTP
OTP Pin Output Current
RI= 24KΩ
90
100
110
µA
V
VOTP-ON
Recovery level on OTP
1.35
1.4
1.45
VOTP-OFF
OTP Threshold Voltage
1.15
1.2
1.25
V
tOTP
OTP Debounce Time
25
µs
RI= 24KΩ
8
Soft-Start Section
Symbol
Parameter
Test Conditions
Min.
Typ.
Max.
Unit
ISS
Constant Current Output for Soft Start
RT= 24KΩ
44
50
56
µA
RD
Discharge RDSON
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
470
-9-
Ω
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
TYPICAL CHARACTERISTICS
Minimum Operating V oltage (V D D - O F F ) vs
S tart-Up Current (ID D - S T ) vs Temperature
25
20
10.5
15
V D D - O F F (V)
I D D - S T (uA)
Temperature
11.0
10
5
10.0
9.5
9.0
8.5
0
8.0
-40
-25
-10
5
20
35
50
Temperature (
65
80
95
110
125
-40
-25
-10
5
)
20
35
50
65
Temperature (
80
95
110
125
)
PWM Fre que ncy (F OSC ) vs Te m pe ra ture
Operating Current (ID D - O P ) vs Temperature
68
10.0
67
66
F OSC (KH z)
ID D - O P (mA)
8.8
7.6
6.4
5.2
65
64
63
4.0
62
-40
-25
-10
5
20
35
50
Temperature (
65
80
95
110
125
-40
-25
-10
5
20
)
35
50
65
Te m pe ra ture (
80
95
110
125
)
V D D Ove r Volta ge Prote ction (V D D - OVP ) vs
Start Threshold Voltage (V D D - O N ) vs Temperature
17.0
Te m pe ra ture
25.5
25.0
16.0
V D D - OVP (V)
V D D - O N (V )
16.5
15.5
15.0
24.5
24.0
14.5
14.0
23.5
-40
-25
-10
5
20
35
50
Temperature (
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
65
80
95
110
125
)
-40
-25
-10
5
20
35
50
Te m pe ra ture (
- 10 -
65
80
95
110
125
)
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
P FC Over V oltage P rotection on FBP FC
Rising Time (t R - P F C ) vs Temperature
120
(OV P F BP F C ) vs Temperature
3.30
104
t R - P F C (ns)
OVP F BPF C (V)
3.28
3.26
3.24
88
72
56
3.22
3.20
40
-40
-25
-10
5
20
35
50
65
Te m pe ra ture (
80
95
110
125
-40
-25
35
50
65
80
95
110
125
110
125
)
110
96
t F - P F C (ns)
V F B- R D Y- H IG H (V)
20
Falling Time (t F - P F C ) vs Temperature
( V F B - R D Y -H I GH ) vs T emperature
2.73
2.71
2.69
82
68
54
2.67
40
2.65
-40
-25
-10
5
20
35
50
65
Te m pe ra ture (
80
95
110
-40
125
-25
-10
5
20
35
50
Temperature (
)
Reference V oltage (V R E F ) vs Temperature
65
80
95
)
Ma xim um D uty C ycle (D C Y M AX ) vs Te m pe ra ture
3.05
98
3.03
97
D C Y M AX (% )
V R E F (V )
5
Temperature (
T hreshold Voltage of F BPF C for R DY high impedance
2.75
-10
)
3.01
2.99
2.97
96
95
94
2.95
93
-40
-25
-10
5
20
35
50
Temperature (
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
65
80
95
110
125
-40
)
-25
-10
5
20
35
50
Te m pe ra ture (
- 11 -
65
80
95
110
125
)
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September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
P WM Open Loop P rotection V oltage (FB O P E N - LO O P )
PWM off to turn on delay time (tO FF-P WM-DLY ) vs
Temperature
4.80
750
4.68
690
tO FF-P WM-DLY (ms)
FB O P E N - LO O P (V )
vs Temperature
4.56
4.44
4.32
4.20
630
570
510
450
-40
-25
-10
5
20
35
50
Temperature (
65
80
95
110
125
-40
-25
-10
5
)
20
35
50
65
Temperature (
PWM Opem Loop Protection Delay Time
80
95
110
125
)
Rising Time (t R - P W M ) vs Temperature
(tO P E N-P WM ) vs Temperature
120
70
102
t R - P W M (ns)
tO P E N-P WM (ms)
65
60
55
84
66
48
50
30
45
-40
-25
-10
5
20
35
50
Temperature (
65
80
95
110
-40
125
-25
20
35
50
65
80
95
110
125
110
125
)
Falling Time (t F - P W M ) vs Temperature
110
Temperature
94
t F - P W M (ns)
0.93
V LI M I T (V )
5
Temperature (
P eak Current Limit Threshold V oltage (V LIM IT ) vs
0.95
-10
)
0.91
0.89
78
62
46
0.87
0.85
30
-40
-25
-10
5
20
35
50
Temperature (
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
65
80
95
110
125
-40
)
-25
-10
5
20
35
50
Temperature (
- 12 -
65
80
95
)
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
OTP Threshold V oltage (V O T P - O F F ) vs
PWM Ma xim um D uty C ycle (D C Y M AXPW M ) vs
Temperature
Te m pe ra ture
83
1.25
1.23
V O T P- O F F (V)
D C Y M AXPW M (% )
81
79
77
1.21
1.19
1.17
75
1.15
73
-40
-25
-10
5
20
35
50
Te m pe ra ture (
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
65
80
95
110
125
-40
-25
-10
5
20
35
50
Te m pe ra ture (
)
- 13 -
65
80
95
110
125
)
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
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.
FIG.1 Start up circuit of the SG6905
PFC ON/OFF Control and RDY Signal for
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.
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.
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.
Switching Frequency and Current
Sources
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 25µA 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.
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
The switching frequency of SG6905 can be programmed
by the resistor RI connected between RI pin and GND.
The relationship is:
FOSC =
1560
RI (kΩ )
(kHz) ----------- (1)
For example, a 24KΩ resistor RI results in a 65 KHz
switching frequency. Accordingly, a constant Current IT
will flow through RI.
IT =
1.2V
RI (kΩ )
(mA) ---------------- (2)
IT is used to generate internal current reference.
- 14 -
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
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
60µA.
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.
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.
IMO × R2 = IS × RS -------------------FIG.3 Interleaved switching pattern
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.
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 ×
IAC × V EA
V RMS
2
(uA) ------------
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
(4)
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 (1µF ~ 10µF) should be connected
to ground. This establishes a dominant pole f1 for the
voltage loop.
(3)
f1 =
- 15 -
1
2π × ZO × CEA
----------------------
(5)
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
The average total input power can be expressed as:
Pin = Vin(rms) × Iin(rms)
∝ VRMS × I MO
∝ VRMS ×
I AC × VEA
2
VRMS
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.
---------------- (6)
Vin
× VEA
R AC
∝ VRMS ×
2
VRMS
= 2×
VEA
R AC
FIG.4 Average current mode control loop
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
- 16 -
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
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 × 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.
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.
The amplitude of the constant current IP is determined by
the internal current reference according to the following
equation:
IP = 2 ×
1.2V
--------------------RI
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
(7)
- 17 -
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
Limited Power Control
Soft-Start
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.
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.
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 24KΩ, then the magnitude of the constant
current will be 100µA. 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
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
- 18 -
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
PACKAGE INFORMATION
20 PINS – PLASTIC SOP (S)
E
H
Detail A
1
F
10
b
c
e
A
D
£ c
L
A2
y
A1
Detail A
Dimension:
Symbol
A
A1
A2
b
c
D
E
e
H
L
F
y
θ˚
Millimeter
Min.
Typ.
2.362
0.101
2.260
Max.
2.642
0.305
2.337
Inch
Min.
Typ.
0.093
0.004
0.089
0.406
0.203
12.598
7.391
12.903
7.595
0.496
0.291
10.643
1.270
0.394
0.016
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
0.508
0.299
0.050
0.508X45˚
0˚
0.104
0.012
0.092
0.016
0.008
1.270
10.007
0.406
Max.
0.419
0.050
0.020X45˚
0.101
8˚
- 19 -
0˚
0.004
8˚
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
20 PINS – PLASTIC SSOP (R)
11
1
10
E1
E
20
"A"
e
b
-H-
A2
GAUGE PLANE
A
0.004
£ c
A1
SEATING PLANE
L
DETAIL : A
L1
Dimension:
Symbol
Millimeter
Min.
A
A1
A2
b
C
D
E
E1
e
L
L1
θ˚
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
Inch
Typ.
1.346
0.102
0.203
0.178
8.560
5.791
3.810
0.406
0˚
8.661
5.994
3.912
0.635 BASIC
0.635
1.041 BASIC
Max.
Min.
Typ.
1.752
0.254
1.499
0.305
0.254
8.738
6.198
3.988
0.008
0.007
0.337
0.228
0.150
1.270
0.016
8˚
0˚
- 20 -
0.053
0.004
0.064
0.006
0.341
0.236
0.154
0.025 BASIC
0.025
0.041 BASIC
Max.
0.069
0.010
0.059
0.012
0.010
0.344
0.244
0.157
0.050
8˚
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007
Product Specification
SG6905
Green mode PFC/Flyback-PWM Controller
© System General Corp.
Version 1.1.1 (IAO33.0060.B1)
- 21 -
www.sg.com.t w • www.fairchildsemi.com
September 27, 2007