FAIRCHILD SG6859A

SG6859A
Low-Cost, Green-Mode PWM Controller for Flyback Converters
Features
Description
ƒ Green-Mode PWM
ƒ Supports the “Blue Angel” Standard
ƒ Low Start-up Current: 9μA
ƒ Low Operating Current: 3mA
ƒ Leading-Edge Blanking
ƒ Constant Output Power Limit
ƒ Universal Input
ƒ Built-in Synchronized Slope Compensation
ƒ Current-Mode Operation
ƒ Cycle-by-cycle Current Limiting
ƒ Under-Voltage Lockout (UVLO)
ƒ Programmable PWM Frequency with Frequency
This highly integrated PWM controller provides several
enhancements designed to meet the low standby-power
needs of low-power SMPS. To minimize standby power
consumption, the proprietary green-mode function
provides off-time modulation to linearly decrease the
switching frequency under light-load conditions. This
green-mode function enables the power supply to meet
even the strictest power conservation requirements.
Hopping
ƒ VDD Over-Voltage Protection (Auto Restart)
ƒ Gate Output Voltage Clamped at 17V
ƒ Low Cost
ƒ Few External Components Required
ƒ Small SOT-26 Package
The BiCMOS fabrication process enables reducing the
start-up current to 9μA and the operating current to
3mA. To further improve power conservation, a large
start-up resistance can be used. Built-in synchronized
slope compensation ensures the stability of peak
current mode control. Proprietary internal compensation
provides a constant output power limit over a universal
AC input range (90VAC to 264VAC). Pulse-by-pulse current
limiting ensures safe operation during short-circuits.
To protect the external power MOSFET from damage by
supply over voltage, the SG6859A’s output driver is
clamped at 17V. SG6859A controllers can be used to
improve the performance and reduce the production
cost of power supplies. The best choice for replacing
linear and RCC-mode power adapters, the SG6859A is
available in 8-pin DIP and 6-pin SOT-26 packages.
Applications
General-purpose switching mode power supplies and
flyback power converters, such as:
ƒ Battery chargers for cellular phones, cordless
phones, PDAs, digital cameras, and power tools
ƒ Power adapters for ink jet printers, video game
consoles, and portable audio players
ƒ Open-frame SMPS for TV/DVD standby and auxiliary
supplies, home appliances, and consumer electronics
ƒ Replacements for linear transformers and RCC SMPS
ƒ PC 5V standby power
Ordering Information
Part Number
Operating Temperature Range
Package
Packing Method
SG6859ATZ
-20°C to +85°C
SOT-26
Tape & reel
SG6859ADZ
-20°C to +85°C
DIP-8
Tube
All packages are lead free per JEDEC: J-STD-020B standard.
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
www.fairchildsemi.com
SG6859A — Low Cost, Green-Mode PWM Controller for Flyback Converters
March 2008
Figure 1. Typical Application
Internal Block Diagram
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Application Diagram
Figure 2. Functional Block Diagram
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
www.fairchildsemi.com
2
SOT-26
DIP-8
GND
GND
GATE
FB
VDD
VDD
FB
RI
SENSE
NC
NC
GATE
SENSE
RI
Figure 3. Pin Configurations
Pin Definitions
DIP
Pin #
SOT
Pin #
Name
Description
1
6
GATE
The totem-pole output driver for driving the power MOSFET.
2
5
VDD
Power supply.
NC
No connection
3
4
5
4
3
6
SENSE
Current sense. This pin senses the voltage across a resistor. When the voltage
reaches the internal threshold, PWM output is disabled. This activates overcurrent protection. This pin also provides current amplitude information for
current-mode control.
RI
A resistor connected from the RI pin to ground generates a constant current
source used to charge an internal capacitor and determine the switching
frequency. Increasing the resistance reduces the amplitude of the current source
and the switching frequency. A 95kΩ resistor RI results in a 50μA constant
current II and a 70kHz switching frequency.
NC
No connection
Feedback. The FB pin provides the output voltage regulation signal. It provides
feedback to the internal PWM comparator, so that the PWM comparator can
control the duty cycle.
7
2
FB
8
1
GND
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Pin Configuration
Ground.
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3
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device
reliability. The absolute maximum ratings are stress ratings only.
Symbol
Parameter
Min.
(1, 2)
Max.
Unit
30
V
VVDD
DC Supply Voltage
VFB
Input Voltage to FB Pin
-0.3
7.0
V
Input Voltage to Sense Pin
-0.3
7.0
V
150
°C
SOT
208.4
°C/W
DIP
82.5
°C/W
150
°C
VSENSE
TJ
Operating Junction Temperature
ΘJA
Thermal Resistance (Junction-to-Air)
TSTG
Storage Temperature Range
TL
ESD
-55
Lead Temperature (Wave Soldering or IR, 10 Seconds)
260
°C
Electrostatic Discharge Capability, Human Body Model
3.5
kV
Electrostatic Discharge Capability, Machine Model
200
V
Notes:
1. All voltage values, except differential voltages, are given with respect to GND pin.
2. Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device.
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Absolute Maximum Ratings
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4
Unless otherwise noted, VDD=15V and TA=25°C.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Units
VDD Section
VDD-OP
Continuously Operation Voltage
22
V
VDD-ON
Turn-on Threshold Voltage
15.5
16.5
17.5
V
VDD-OFF
Turn-off Threshold Voltage
8.5
9.5
10.5
V
IDD-ST
Startup Current
VDD=VDD-ON – 0.1V
9
15
μA
IDD-OP
Operating Supply Current
VDD=15V, CL=1nF
3.0
3.5
mA
VDD Over-voltage Protection Level
Auto Restart
25
26
V
VDD-OVP
tD-VDDOVP VDD Over-voltage Protection Debounce
VDD-G OFF
24
Auto Restart
VDD Low-threshold Voltage to Exit
Green-off Mode
125
μs
VDD-OFF
+1
V
5
kΩ
Feedback Input Section
ZFB
VFB-OPEN
VFB-OL
Input Impedance
FB Output High Voltage
FB Open-loop Trigger Level
tD-OLP
Delay of FB Pin Open-loop Protection
VFB-N
Green-Mode Entry FB Voltage
VFB-G
Green-Mode Ending FB Voltage
SG
5
Green-Mode Modulation Slope
V
4.3
4.6
2.60
2.85
4.9
56
ms
3.10
2.2
RI=95kΩ
40
V
V
V
75
100
55
100
Hz/mV
Current-Sense Section
ZSENSE
Input Impedance
10
tPD
Delay to Output
40
kΩ
VSTHFL
Flat Threshold Voltage for Current Limit
VSTHVA
Valley Threshold Voltage for Current Limit
0.75
0.80
0.85
V
Leading-Edge Blanking Time
270
320
370
ns
tLEB
DCYSAW
1
ns
Duty Cycle of SAW Limit
V
40
%
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Electrical Characteristics
Oscillator Section
Center Frequency
70
75
Frequency
THOP
Hopping Period
RI=95kΩ
3.7
ms
Green-Mode Frequency
RI=95kΩ
20
kHz
FDV
Frequency Variation vs. VDD Deviation
VDD=13.5 to 22V
FDT
Frequency Variation vs. Temperature
Deviation
TA=-20 to 85°C
FOSC-G
Hopping Range
RI=95kΩ
65
FOSC
kHz
±4.9
0
0.02
2.00
%
2
%
72
%
1.4
V
Output Section
DCYMAX
Maximum Duty Cycle
VGATE-L
Output Voltage Low
VDD=15V, Io=20mA
VGATE-H
Output Voltage High
VDD=13.5V, Io=20mA
tr
Rising Time
VDD=15V, CL=1nF
150
ns
tf
Falling Time
VDD=15V, CL=1nF
55
ns
Output Clamp Voltage
VDD=22V
VGATECLAMP
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
62
67
8
16
V
17
18
V
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5
13.0
16.8
12.0
VDD-OFF (V)
VDD-ON (V)
17.0
16.6
16.4
16.2
11.0
10.0
9.0
16.0
8.0
-40
-25
-10
5
20
35
50
65
80
95
110
125
-40
-25
-10
5
Temperature (℃)
50
65
80
95
110
125
Figure 5. Turn-off Threshold Voltage (VDD-ON)
vs. Temperature
3.0
3.5
2.5
3.3
IDD-OP (mA)
IDD-ST (μA)
35
Temperature (℃)
Figure 4. Turn-on Threshold Voltage (VDD-ON)
vs. Temperature
2.0
1.5
1.0
3.1
2.9
2.7
0.5
2.5
-40
-25
-10
5
20
35
50
65
80
95
110
125
-40
-25
-10
5
Temperature (℃)
20
35
50
65
80
95
110
125
Temperature (℃)
Figure 6. Start-up Current (IDD-ST) vs. Temperature
Figure 7. Operating Supply Current (IDD-OP)
vs. Temperature
70.0
70.0
69.0
69.0
DCYMAX (%)
FOSC (KHz)
20
68.0
67.0
66.0
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Typical Performance Characteristics
68.0
67.0
66.0
65.0
65.0
-40
-25
-10
5
20
35
50
65
80
95
110
125
-40
Temperature (℃)
-10
5
20
35
50
65
80
95
110
125
Temperature (℃)
Figure 8. Center Frequency (FOSC) vs. Temperature
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
-25
Figure 9. Maximum Duty Cycle (DCYMAX) vs.
Temperature
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6
3.0
3.0
2.8
2.8
2.6
VFB-G (V)
VFB-N (V)
3.2
2.6
2.4
2.4
2.2
2.2
2.0
-40
-25
-10
5
20
35
50
65
80
95
110
125
-40
-25
-10
5
20
Temperature (℃)
Figure 10. Green-Mode Entry FB Voltage (VFB-N)
vs. Temperature
50
65
80
95
110
125
Figure 11. Green-Mode Ending FB Voltage (VFB-G)
vs. Temperature
350.0
3.5
330.0
3.0
IDD-OP (mA)
tLEB (ns)
35
Temperature (℃)
310.0
290.0
2.5
2.0
1.5
270.0
1.0
250.0
-40
-25
-10
5
20
35
50
65
80
95
110
125
12
Figure 12. Leading-Edge Blanking Time (tLEB)
vs. Temperature
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
13
14
15
16
17
18
19
20
21
22
23
24
VDD (V)
Temperature (℃)
Figure 13. Operating Supply Current vs. VDD Voltage
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Typical Performance Characteristics
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7
output GATE drive is turned off following a short
propagation delay, tPD. This propagation delay
introduces an additional current proportional to
tPD•VIN/LP. The propagation delay is nearly constant,
regardless of the input line voltage VIN. Higher input line
voltages result in larger additional currents. At high
input line voltages, the output power limit is higher than
at low input line voltages. To compensate for this output
power limit variation across a wide AC input range, the
threshold voltage is adjusted by adding a positive ramp.
This ramp signal rises from 0.8V to 1V, then flattens out
at 1V. A smaller threshold voltage forces the output
GATE drive to terminate earlier, which reduces the total
PWM turn-on time and makes the output power equal to
that of low line input. This proprietary internal
compensation ensures a constant output power limit for
a wide AC input voltage range (90VAC to 264VAC).
SG6859A devices integrate many useful designs into
one controller for low-power, switch-mode power
supplies. The following descriptions highlight some of
the features of the SG6859A series.
Start-up Current
The start-up current is only 9μA. Low start-up current
allows a start-up resistor with high resistance and lowwattage to supply the start-up power for the controller. A
1.5MΩ, 0.25W, start-up resistor and a 10µF/25V VDD
hold-up capacitor are sufficient for an AC-to-DC power
adapter with a wide input range (100VAC to 240VAC).
Operating Current
The operating current has been reduced to 3mA. The
low operating current results in higher efficiency and
reduces the VDD hold-up capacitance requirement.
Under-Voltage Lockout (UVLO)
Green-Mode Operation
The turn-on and turn-off thresholds are fixed internally
at 16.5V and 9.5V. During start-up, the hold-up
capacitor must be charged to 16.5V through the start-up
resistor to enable the SG6859A. The hold-up capacitor
continues to supply VDD until power can be delivered
from the auxiliary winding of the main transformer. VDD
must not drop below 9.5V during this start-up process.
This UVLO hysteresis window ensures that hold-up
capacitor is adequate to supply VDD during start-up.
The proprietary green-mode function provides off-time
modulation to linearly decrease the switching frequency
under light-load conditions. On-time is limited to provide
stronger protection against brownouts and other
abnormal conditions. The feedback current, which is
sampled from the voltage feedback loop, is taken as the
reference. Once the feedback current exceeds the
threshold current, the switching frequency starts to
decrease. This green-mode function dramatically
reduces power consumption under light-load and zeroload conditions. Power supplies using the SG6859A
can meet even the strictest regulations regarding
standby power consumption.
Gate Output
The BiCMOS output stage is a fast totem pole gate
driver. Cross conduction has been avoided to minimize
heat dissipation, increase efficiency, and enhance
reliability. The output driver is clamped by an internal
17V Zener diode to protect power MOSFET transistors
against undesired over-voltage gate signals.
Oscillator Operation
A resistor connected from the RI pin to ground
generates a constant current source used to charge an
internal capacitor. The charge time determines the
internal clock speed and the switching frequency.
Increasing the resistance reduces the amplitude of the
input current and the switching frequency. A 95kΩ RI
resistor results in a 50µA constant current II and a
70kHz switching frequency. The relationship between RI
and the switching frequency is:
fPWM =
6650
(kHz)
RI(kΩ)
Built-in Slope Compensation
The sensed voltage across the current-sense resistor is
used for current-mode control and pulse-by-pulse
current limiting. Built-in slope compensation improves
stability and prevents sub-harmonic oscillations due to
peak-current mode control. The SG6859A has a
synchronized, positively-sloped ramp built-in at each
switching cycle. The slope of the ramp is:
(1)
0.36 × Duty
Duty(max.)
Leading-Edge Blanking
Each time the power MOSFET is switched on, a turn-on
spike occurs at the sense-resistor. To avoid premature
termination of the switching pulse, a 320ns leadingedge blanking time is built in. Conventional RC filtering
can be omitted. During this blanking period, the currentlimit comparator is disabled and cannot switch off the
gate driver.
(2)
Noise Immunity
Noise from the current sense or the control signal can
cause significant pulse-width jitter, particularly in
continuous-conduction mode (CCM). While slope
compensation helps alleviate these problems, further
precautions should still be taken. Good placement and
layout practices should be followed. Avoiding long PCB
traces and component leads, locating compensation
and filter components near the SG6859A, and increasing
power MOS gate resistance improve performance.
Constant Output Power Limit
When the SENSE voltage across the sense resistor,
RS, reaches the threshold voltage (around 1V), the
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Operation Description
www.fairchildsemi.com
8
F1
L1
1
2
1
L
BD1
C3
R3
R1
CX1
2
4
C1
C2
R5
R4
T1
R2
3
L2
D4
1,2
2
1
1
2
VO
1
10
N
1
9
R10
2
D1
2
U1
GND GATE
6
R7
C8
D5
C9
Q1
1
2
1
C7
8
5
3
FB
VDD
RI
SENSE
5
7
3
2
3,4
GND
R15
4
C6
C11
R9
R6
R8
D2
1
2
R11
1
4
C4
R13
U2
2
3
R14
C10
3
CY1
U3
1
2
R12
Figure 14. Reference Circuit
BOM
Reference
BD1
Component
Reference
Component
BD 1A/500V
L2
10µH 6mm
CX1 (Optional)
XC 0.1μF
Q1
MOSFET 1A/600V
CY1 (Optional)
YC 102P/400V (Y1)
R1,R2
R 750KΩ 1206
C1
CC 103P/500V
R3,R4
R 47KΩ 1206
C2
EC 10μF/400V 105°C
R5
R 47Ω 1206
C3
CC 102P/500V
R6
R 4.7Ω 1206
C4
EC 10μF/50V
R7
R 100Ω 0805
C6
CC 472P 0805
R8
R 10Ω 1206
C7 (Optional)
CC 102P/100V 1206
R9
R 100KΩ 0805
C8
EC 470μF/10V 105°C
R10 (Optional)
R 10Ω 1206
C9
EC 220μF/10V 105°C
R11
R 100Ω 1/8W
C10
CC 222P 0805
R12
R 33KΩ 0805
C11
N.C.
R13
R 33KΩ 1/8W
D1
Diode FRI07
R14
R 4.7KΩ 0805
D2
Diode FR102
R15
R 0Ω 0805
D4
Diode SB360
T1
EE-16
D5 (Optional)
ZD 6.8V 0.5W
U1
IC SG6859A
F1
R 1Ω/0.5W
U2
PC817
L1
20mH 6•8mm
U3
TL431
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Applications Information
www.fairchildsemi.com
9
D
Θ ¢X
5
E1
8
e
E
B
A
A1
A2
4
1
L
b1
b
e
Figure 15. 8-Pin Dip-8 Package
Dimensions
Symbol
Millimeters
Min.
Typ.
A
0.381
A2
3.175
b
0.015
3.302
3.429
0.125
E
9.271
6.223
6.350
0.135
0.018
10.160
0.355
7.620
e
0.130
0.060
0.457
9.017
Max.
0.210
1.524
b1
E1
Typ.
5.334
A1
D
Inches
Min.
Max.
0.365
0.400
0.300
6.477
0.245
2.540
0.250
0.255
0.100
L
2.921
3.302
3.810
0.115
0.130
0.150
eB
8.509
9.017
9.525
0.335
0.355
0.375
θ˚
0˚
7˚
15˚
0˚
7˚
15˚
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Physical Dimensions
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10
D
Detail A
b
4
E
E1
6
1
e
c
3
e1
1
R
θ
A
A2
1
L2
R
L
A1
θ
L1
1
θ
Detail A
Figure 16. 6-Pin SOT-26 Package
Dimensions
Symbol
Millimeters
Min.
Typ.
Inches
Min.
Max.
Typ.
Max.
A
1.45
0.057
A1
0.15
0.006
A2
0.90
1.30
0.036
b
0.30
0.50
0.011
c
0.08
0.22
0.003
D
1.15
2.90
0.045
0.009
0.114
2.80
0.110
E1
1.60
0.063
e
0.95
0.037
e1
1.90
0.075
0.30
L1
0.60
0.020
0.60
L2
R
0.45
0.051
0.020
E
L
0.018
0.024
0.024
0.25
0.010
0.10
0.004
R1
0.10
0.25
0.004
θ°
0°
4°
8°
0°
4°
8°
θ1°
5°
10°
15°
5°
10°
15°
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
Physical Dimensions (Continued)
0.010
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11
SG6859A — Low-Cost, Green-Mode PWM Controller for Flyback Converters
© 2007 Fairchild Semiconductor Corporation
SG6859A Rev. 1.0.0
www.fairchildsemi.com
12