System General SG6848D, SG6848T Schematic [ru]
Product Specification
O
UTPU
Low Cost Green-Mode PWM Controller for Flyback Converters SG6848
FEATURES
Green-Mode PWM
Supports the “Blue Angel” Standard
Low Start-up Current (5uA)
Low Operating Current (2mA)
Leading-Edge Blanking
Constant Output Power Limit
Universal Input
Built-in Synchronized Slope Compensation
Current Mode Operation
Cycle-by-cycle Current Limiting
Under Voltage Lockout (UVLO)
Programmable PWM Frequency
Gate Output Voltage Clamped at 15V
Low Cost
Few External Components Required
Small SOT-26 Package
APPLICATIONS
General-purpose switching mode power supplies and
flyback power converters, such as
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, and consumer
electronics
Replacements for linear transformers and RCC
SMPS
PC 5V standby power.
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 easily meet even the strictest power
conservation requirements.
The BiCMOS fabrication process enables reducing
the start-up current to 5uA, and the operating current to
2mA. 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 even during short-circuits.
To protect the external power MOSFET from being
damaged by supply over voltage, the SG6848’s output
driver is clamped at 15V. SG6848 controllers can be used
to improve the performance and reduce the production
cost of power supplies. The SG6848 is the best choice for
replacing linear and RCC-mode power adapters. It is
available in 8-pin DIP and 6-pin SOT-26 packages.
TYPICAL APPLICATI ON
© System General Corp. - 1 - www.sg.com.tw
Version 1.2(IRO33.0010.B0) May.06, 2003
From bridge rectifier
R9
95k
C6
472p
120~ 380VDC
FB
SG6848
VDD
GND
RIN
1.5M
SENSE
T
From auxiliary winding
C
IN
10u
R7
100
R
4.7
S
Product Specification
1
W
Low Cost Green-Mode PWM Controller for Flyback Converters SG6848
MARKING DI A G RA MS
PI N CONFIGURATION
M: Mask Version
MAYW
Y: Year; WW: Work Week
1
8
SG6848D
XXXXXXXYYWWV
XXXXXXX: Wafer Lot
YY: Year; WW: Week
V: Assembly Location
1
GND
FB
RI
GATE
VDD
NC
SENSE
SOT-26
2
3
DIP-8
1
2
3
4
GATE
6
5
VDD
4
SENSE
GND
8
FB
7
6
NC
5
RI
ORDERING INFORMATION
Part Number PWM Frequency Package
SG6848T 70kHz 6-Pin SOT-26
SG6848D 70kHz 8-pin DIP-8
PIN DESCRIPTI O NS
Name
GATE 1 / (6) Driver Output The totem- pole output driver for driving the power MOSFET.
VDD 2 / (5) Supply Power supply.
NC 3 NC pin.
SENSE 4 / (4) Analog Input
RI 5 / (3)
NC 6 NC pin.
FB 7 / (2) Analog Input
GND 8 / (1) Supply Ground.
Pin No.
DIP-8 / (SOT-26)
Type Function
Current s ense. This pin senses the voltage across a resistor. W hen the voltage r eaches
the internal thr eshold, PWM output is disabled. This activates over-curr ent protection.
This pin also pr ovides current amplitude inf ormation for current-mode control.
A resistor connected from the RI pin to ground will generate a constant current source for
Analog
Input/Output
the SG6848. This current is used to charge an internal capacitor, to determine the
switching frequency. Increasing the resistance will reduce the amplitude of the current
source and reduce the switching fr equency. A 95kΩ resistor R
current I
Feedback. The FB pin provides the output voltage regulation signal. It provides feedback
to the internal PW M comparator, so that the PW M comparator c an c ontrol the duty cycle.
and a 70kHz switching frequency.
i
results in a 50uA constant
i
© System General Corp. - 2 - www.sg.com.tw
Version 1.2(IRO33.0010.B0) May.06, 2003
Product Specification
Low Cost Green-Mode PWM Controller for Flyback Converters SG6848
BLOCK DIAGRAM
VDD 2 (5)
GND
8 (1)
+
_
UVLO
16.3V/11.7V
Internal
Bias
RI
5 (3)
OSC
Q
S
R
Green
Mode
Controller
OCP
Comp
Slope
Compensation
PWM
Comp
ON/OFF
Driver
Vlimit
ramp
VDD
Blanking
Circuit
4.8V
1 (6)
4 (4)
7 (2)
GATE
SENSE
FB
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VDD DC Supply Voltage *
Zener Clamp
Zener Current
VFB Input Voltage to FB Pin -0.3 to 6 V V
V
Input Voltage to Sense Pin -0.3 to 6V V
Sense
Pd Power Dissipation 300 mW
TJ Operating Junct ion Temperature 150 ℃
RθJA Thermal Resistance (Junction t o Air)
T
Storage Temper ature Range -55 to +150 ℃
stg
T
L
ESD Capability, HBM Model 3.0 kV
ESD Capability, Model 300 V
Lead Temperature (Soldering)
SOT-26 208.4 °C/W
DIP-8 82.5 °C/W
20 sec SOT-26
10 sec DIP-8
25
26
10
220
260
* All voltage values, except differential voltages, are given with respect to the network ground terminal.
V
V
mA
°C
© System General Corp. - 3 - www.sg.com.tw
Version 1.2(IRO33.0010.B0) May.06, 2003
Product Specification
Low Cost Green-Mode PWM Controller for Flyback Converters SG6848
RECOMMENDED OPERATING CONDITIONS
Symbol Parameter Value Unit
VDD DC Supply Voltage ≦20 V
Ta Operating Ambient Temperature -30 to +85 ℃
ELECTRICAL CHARACTERISTICS (TA = 25°°°°C, VDD=15V)
Feedback Input Section
Symbol Parameter Test Condition Min. Typ. Max. Unit
Ioz Zero Duty Cycle Input Current 1.3 2.0 mA
Vop Open Loop Voltage 4.5 V
Current Sense Section
Symbol Parameter Test Condition Min. Typ. Max. Unit
Zcs Input Impedance 10 kΩ
TPD Delay to Output 150 200 nsec
V
Current Limit Flatten Threshold Voltage 1.0 V
TH,FLT
V
Current Limit Valley Threshold Voltage 0.80 0.85 0.90 V
TH,VALLEY
Oscillator Section
Symbol Parameter Test Condition Min. Typ. Max. Unit
F
Frequenc y RI=95kΩ 65 70 75 kHz
osc
F
Green-Mode Frequenc y RI=95kΩ 13 15 kHz
osc -green
Ig Green-Mode FB Input Current 1.16 mA
In
Sg Green-Mode Modulation Slope RI=95kΩ 300 Hz/uA
Fdv Frequenc y Variation versus VDD Deviation VDD=12 to 20V 0.02 2 %
Fdt Frequenc y Variation versus T emp. D eviation TA=-30 to 85 ℃ 2 %
Green-Mode Start Threshold FB Input Current
= 0.3mA for a Maximum Duty Cycle
I
n
1 mA
PWM Section
Symbol Parameter Test Condition Min. Typ. Max. Unit
DC
Maximum Dut y Cycle 70 75 80 %
(MAX)
DC
Minimum D uty Cycle - 1 2 %
(MIN)
Bnk Leading-Edge Blanking Time 250 nsec
Output Section
Symbol Parameter Test Condition Min. Typ. Max. Unit
Vol Output Voltage Low VDD=15V, Io=20mA 1.5 V
Voh Output Voltage High VDD=15V, Io=20mA 8 V
tr Rising Time VDD=15V, CL=1nF 50 200 nsec
tf Falling Time VDD=15V, CL=1nF 30 150 nsec
V
Output Clamp Voltage VDD=20V 15 17 V
CLAMP
© System General Corp. - 4 - www.sg.com.tw
Version 1.2(IRO33.0010.B0) May.06, 2003
Product Specification
Low Cost Green-Mode PWM Controller for Flyback Converters SG6848
Under Voltage Lockout Section
Symbol Parameter Test Condition Min. Typ. Max. Unit
V
Start Threshold Voltage TA=25°C 15.3 16.3 17.3 V
TH(ON)
V
Min. Operating Voltage TA=25°C 10.9 11.7 12.5 V
DD(min)
Total Standby Current Section
Symbol Parameter Test Condition Min. Typ. Max. Unit
I
Start-up Current VDD=15V 5 30 uA
DD ST
I
Operating Supply Current VDD=15V 2 5 mA
DD OP
© System General Corp. - 5 - www.sg.com.tw
Version 1.2(IRO33.0010.B0) May.06, 2003
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