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SG6858 — Low-Cost, Green-Mode, PWM Controller for Flyback Converters
September 2009
SG6858
Low-Cost, Green-Mode, PWM Controller for Flyback
Converters
Features
Green-Mode PWM
Supports the ”Blue Angel” Standard
Low Startup Current: 10µA (Maximum)
Low Operating Current: 2.5mA
Leading-Edge Blanking (LEB)
Constant Output Power Limit
Built-in Synchronized Slope Compensation
Current-Mode Operation
Cycle-by-Cycle Current Limiting
Under-Voltage Lockout (UVLO)
Programmable PWM Frequency
V
DD
Over-Voltage Protection with Auto-Restart
Gate Output Voltage Clamped at 17V
Few External Components Required
SSOT-26 and DIP-8 Packages Available
Description
This highly integrated PWM controller provides several
special 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.
The BiCMOS fabrication process enables reducing the
startup current to 10µA and the operating current to
2.5mA. To further improve power conservation, a large
startup 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 (90V
AC
to 264V
AC
). Pulse-by-pulse
current limiting ensures safe operation even during
short circuits.
To protect the external power MOSFET from being
damaged by supply over voltage, the output driver is
clamped at 17V. SG6858 controllers can improve the
performance and reduce the production cost of power
supplies. The SG6858 replaces linear and RCC-mode
power adapters. It is available in 8-pin DIP and 6-pin
SSOT-26 packages.
Applications
Battery chargers for cellular phones, cordless
phones, PDAs, digital cameras, and power tools
Power adapters for ink jet printers, video game
consoles, and portable audio players
Open-frame SMPS for TV/DVD standby and other
auxiliary supplies, home appliances, PC 5V
standby power, and consumer electronics
Replacements for linear transformers and RCC
SMPS
Offline High Brightness (HB) LED drivers
Ordering Information
Part Number
SG6858TZ
SG6858DZ
Operating Temperature Range
-40 to +125°C
-40 to +125°C
Eco Status
RoHS
RoHS
Package
6-Pin SSOT-26
8-Pin DIP-8
Packing Method
Tape & Reel
Tube
For Fairchild’s definition of Eco Status, please visit:
http://www.fairchildsemi.com/company/green/rohs_green.html.
© 2008 Fairchild Semiconductor Corporation
SG6858 • Rev. 1.2.4
www.fairchildsemi.com
SG6858 — Low-Cost, Green-Mode, PWM Controller for Flyback Converters
Typical Application
L
EMI
AC Input
N
Filter
Bridge
Rectifier
Diode
+
C
Bulk
R
Start
R
SN
D
VDD
+
C
VDD
5
R
SN2
C
SN2
C
SN
N
P
D
SN
N
S
D
R
+
C
O1
C
O2
V
O
+
ZD
O
V
O
-
N
A
VDD
3
RI
GATE
6
SG6858
SENSE
4
GND
1
R
RI
2
FB
R
G
R
LF
R
SENSE
R
d
R
1
C
FB
C
LF
PC817
R
F
TL431
R
2
C
F
Figure 1. Typical Application
Block Diagram
GND
1(8)
OVP
25V
OSC
S
R
Q
Soft
Driver
RI
3(5)
V
DD
6(1) GATE
VDD 5(2)
Internal
BIAS
Vlimit ramp
+
UVLO
Slope
Compensation
16.5V/11.5V
Green
Mode
Controller
3R
2R
Blanking
Circuit
5V
4(4) SENSE
2(7) FB
SOT(DIP)
Figure 2. Block Diagram
© 2008 Fairchild Semiconductor Corporation
SG6858 • Rev. 1.2.4
www.fairchildsemi.com
2
SG6858 — Low-Cost, Green-Mode, PWM Controller for Flyback Converters
Marking Information
XXX:AAI=SG6858
TT: Die run code
●:
Year code
—
: Week code
Figure 3. SSOT-26
F:
Fairchild Logo
Z: Assembly Plant Code
X: Year Code
Y: Week Code
TT: Die Run Code
T: N=DIP
P: Y=Green Package
M: Manufacture flow code
Figure 4. DIP-8
Pin Configuration
GND
FB
RI
1
2
3
SOT - 26
6
5
4
GAT E
GATE
VDD
1
2
3
4
DIP-8
8
7
6
5
GND
FB
NC
RI
VDD
NC
SENS E
SE NSE
Figure 5. Pin Configurations
Pin Definitions
Pin #
DIP-8 SSOT-26
1
2
3
4
4
6
5
GATE
VDD
NC
Totem-pole output driver for the power MOSFET.
Power supply.
No connection.
Name Description
Current sense. This pin senses the voltage across a resistor. When the voltage
SENSE reaches the internal threshold, PWM output is disabled. This activates over-current
protection. This pin provides current amplitude information for current-mode control.
A resistor connected from the RI pin to ground generates a constant current source.
This current is used to charge an internal capacitor to determine the switching
frequency. Increasing the resistance reduces the amplitude of the current source
and reduces the switching frequency. A 95kΩ resistor, R
I,
results in a 50µA constant
current, I
I,
and a 70kHz switching frequency.
No connection.
Feedback. The FB pin provides the output voltage regulation signal, and feedback to
the internal PWM comparator, so the PWM comparator can control the duty cycle.
Ground.
www.fairchildsemi.com
3
5
3
RI
6
7
8
2
1
NC
FB
GND
© 2008 Fairchild Semiconductor Corporation
SG6858 • Rev. 1.2.4
SG6858 — Low-Cost, Green-Mode, PWM Controller for Flyback Converters
Absolute Maximum Ratings
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. All voltage values, except differential voltages, are
given with respect to GND pin.
Symbol
V
DD
V
FB
V
SENSE
R
ΘJC
T
J
T
STG
T
L
ESD
Supply Voltage
Input Voltage to FB Pin
Input Voltage to SENSE Pin
Parameter
Min.
-0.3
-0.3
SSOT
DIP
-40
-55
Max.
30
7.0
7.0
208.4
82.5
+125
+150
260
3.0
0.2
Unit
V
V
V
°C/W
°C
°C
°C
kV
Thermal Resistance (Junction-to-Case)
Operating Junction Temperature
Storage Temperature Range
Lead Temperature, Wave Soldering, 10 Seconds
Electrostatic Discharge Capability
Human Body Model, JESD22-A114
Machine Model, JESD22-A115
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to Absolute Maximum Ratings.
Symbol
V
DD
T
A
DC Supply Voltage
Parameter
Operating Ambient Temperature
Min.
-40
Max.
22
+125
Unit
V
°C
© 2008 Fairchild Semiconductor Corporation
SG6858 • Rev. 1.2.4
www.fairchildsemi.com
4
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