Product Specification
Highly-Integrated Green-Mode PWM Controller
SG6846
System General Corp. - 1 - www.sg.com.tw
Version 1.1(IAO33.0008.B1) Jan. 23, 2006
FEATURES
Two-level OCP with 96mS delay time
Peak-current-mode operation with cycle-by-cycle
current limiting
PWM frequency continuously decreasing w/ burst
mode at light loads
Low start-up current (8uA)
Low operating current (3.7mA)
VDD over-voltage protection (OVP)
AC input brownout protection with hysteresis
Programmable over-temperature protection (OTP)
Constant power limit over universal AC input range
Internal latch circuit for OTP, OVP, OCP
Very few external components
APPLICATIONS
General-purpose switch mode power supplies and
flyback power converters, including:
Power adapters
Open-frame SMPS
Specifically fit for SMPS with surge-current output,
such as for printers, scanners, motor drivers, etc.
DESCRIPTION
The highly integrated SG6846 series of PWM
controllers provides several features to enhance the
performance of flyback converters. To minimize standby
power consumption, a proprietary green-mode function
provides off-time modulation to continuously decrease
the switching frequency under light-load conditions.
Under zero-load conditions, the power supply enters
burst-mode. This completely shuts off PWM output. The
output restarts just before the supply voltage drops below
the UVLO lower limit. This green-mode function enables
power supplies to easily meet international power
conservation requirements.
The SG6846 is especially designed for SMPS with
surge-current output. It is incorporated with a two-level
OCP function. Besides the cycle-by-cycle current limiting,
if the switching current is higher than 2/3 of the
peak-current threshold for a delay time, over-current
protection will be activated such that the SG6846 will be
totally shutdown. Other protection functions include: AC
input brownout protection with hysteresis, and VDD
over-voltage protection. For over-temperature protection,
an external NTC thermistor can be applied to sense the
ambient temperature. When OCP, VDD OVP, or OTP are
activated, an internal latch circuit is used to latch-off the
controller. The latch will reset when the VDD supply is
removed.
Other features of this controller include: Built-in
synchronized slope compensation, proprietary internal
compensation for constant output power limit over
universal AC input range. Also, the gate output is clamped
at 18V to protect the external MOSFET from over-voltage
damage.
The SG6846 series controllers are available in both
8-pin DIP and SO packages.
TYPICAL APPLICATION
Product Specification
Highly-Integrated Green-Mode PWM Controller
SG6846
System General Corp. - 2 - www.sg.com.tw
Version 1.1(IAO33.0008.B1) Jan. 23, 2006
MARKING DIAGRAMS PIN CONFIGURATION
ORDERING INFORMATION
Part Number
Package
OTP Mode
SG6846LS
8-Pin SOP
Latch off
SG6846LD
8-Pin DIP
Latch off
SG6846CS 8-Pin
SOP
Hysteresis
SG6846CD 8-Pin
DIP
Hysteresis
SG6846LSZ
8-Pin SOP (Lead Free)
Latch off
SG6846LDZ
8-Pin DIP (Lead Free)
Latch off
SG6846CSZ
8-Pin SOP (Lead Free)
Hysteresis
SG6846CDZ
8-Pin DIP (Lead Free)
Hysteresis
SG6846FTP
MXXXXXXYYWWV
8
1
F:
L = OTP Latch
C = Hysteresis OTP
T
: D = DIP, S = SOP
P
: Null = regular
Z = Lead free
M
: Mask version
XXXXXX
: Wafer Lot
YY
: Year;
WW
: Week
V
: Assembly Location
RI
VIN
GATE
VDD
SENSE
RT
GND
FB
3
1
2
5
6
8
7
4
Product Specification
Highly-Integrated Green-Mode PWM Controller
SG6846
System General Corp. - 3 - www.sg.com.tw
Version 1.1(IAO33.0008.B1) Jan. 23, 2006
PIN DESCRIPTIONS
Pin No. Symbol Function
Description
1 GND
Ground
Ground.
2 FB Feedback
The signal from the external compensation circuit is fed into this pin. This FB pin and the
current-sense signal from Pin 6 determine the PWM duty cycle.
3 VIN
Line-voltage
Detection
Line-voltage detection. The line-voltage detection is used for brownout protection with
hysteresis. Constant output power limit over universal AC input range is also achieved using
this VIN signal. It is suggested to add low pass filter to filter out line ripple on bulk capacitor.
4 RI
Reference
Setting
A resistor from the RI pin to ground will generate a reference current source inside SG6846.
This determines the switching frequency. Increasing the resistance will reduce the switching
frequency. Using a 26k resistor Ri results in a 65kHz switching frequency.
5 RT
Temperature
Detection
For over-temperature protection. An external NTC thermistor is connected from this pin to
GND pin. The impedance of the NTC will decrease at high temperatures. Once the voltage
of the RT pin drops below a threshold, PWM output will be disabled.
6 SENSE
Current
Sense
Current sense. The sensed voltage is used for peak-current-mode control and
cycle-by-cycle current limiting. If the switching current is higher than 2/3 of the peak-current
threshold for longer than 96ms, over-current protection will be activated. This two-level OCP
feature is especially suitable for SMPS with surge current output.
7 VDD
Power
Supply
Power Supply. The internal protection circuit will disable PWM output when VDD over
voltage.
8 GATE
Driver
Output
The totem-pole output driver for the power MOSFET. A soft driving waveform is
implemented for improved EMI.
BLOCK DIAGRAM (OTP LATCH VERSION)
Product Specification
Highly-Integrated Green-Mode PWM Controller
SG6846
System General Corp. - 4 - www.sg.com.tw
Version 1.1(IAO33.0008.B1) Jan. 23, 2006
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
Test Condition
Value
Unit
V
DD
Supply
Voltage
25
V
V
L
Input Voltage to VIN, FB, SENSE, RT, RI Pin
-0.3 to 7V
V
P
D
Power
Dissipation
at T
A
< 50C DIP
SOP
800
400
mW
R
J-C
Thermal
Resistance
Junction-Case DIP
SOP
67.1
41.2
C/W
T
J
Operating Ambient Temperature
-40 to 125
C
T
STG
Storage Temperature Range
-65 to +150
C
T
L
Lead Temperature (Soldering)
10 sec DIP
10 sec SOP
260
230
C
*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 JUNCTION TEMPERATURE: -30C ~ 85C*
*For proper operation
ELECTRICAL CHARACTERISTICS (VDD = 15V, T
A
= 27C, unless noted)
VDD Section
Symbol Parameter
Test
Condition Min. Typ. Max.
Unit
V
OP
Continuously Operating Voltage
20
V
V
TH-ON
On Threshold Voltage
15.5
16.5
17.5
V
V
TH-OFF
Off Threshold Voltage
9.5
10.5
11.5
V
I
DD-ST
Start-Up Current
VDD = 15V
8
30
uA
I
DD-OP
Operating Supply Current
GATE Open
3.7
5
mA
V
DD-OVP
VDD Over Voltage Protection (Latch off)
22.6
23.6
24.6
V
T
VDD-OVP
VDD OVP Debounce Time
RI = 26K
100
usec
I
DD-OVP
VDD OVP Latch-up Holding Current
VDD = 5V, T
A
= 27
o
C
45
uA
V
DD-TH-G
VDD Low-threshold Voltage to Exit Green-OFF
Mode
V
TH(OFF)
+
1.25
V
VIN Section
Symbol Parameter
Test
Condition Min. Typ. Max.
Unit
V
IN-OFF
PWM Turn-off Threshold Voltage
0.67
0.72
0.77
V
V
IN-ON
PWM Turn-on Threshold Voltage
V
IN-OFF
+
0.2
V
Feedback Input Section
Symbol Parameter
Test
Condition Min. Typ. Max.
Unit
A
V
Input-Voltage to Current-Sense Attenuation
1/4.2
V/V
Z
FB
Input
Impedance
4
5.5
7
K
V
FB0
FB Pin open voltage
6.2
V
Product Specification
Highly-Integrated Green-Mode PWM Controller
SG6846
System General Corp. - 5 - www.sg.com.tw
Version 1.1(IAO33.0008.B1) Jan. 23, 2006
Current Sense Section
Symbol Parameter
Test
Condition Min. Typ. Max.
Unit
Z
CS
Input
Impedance
12
k
T
PD
Delay
to
Output
100 200 nsec
B
NK
Leading Edge Blanking Time
360
nsec
V
TH-P
@V
IN
=1V Threshold Voltage for Current Limit
VIN = 1V, RI = 26k
0.78 0.83 0.88 V
V
TH-P
@V
IN
=3V Threshold Voltage for Current Limit
VIN =3V, RI = 26k 0.65 0.70 0.75 V
V
TH-O
@V
IN
=1V 2/3 Threshold Voltage for Current Limit
VIN = 1V, RI = 26k
0.56 0.61 0.66 V
V
TH-O
@V
IN
=3V 2/3 Threshold Voltage for Current Limit
VIN =3V, RI = 26k 0.46 0.51 0.56 V
T
DELAY-OCP
The Delay Time for Over-current Protection RI = 26K 82
96
110
msec
Oscillator Section
Symbol Parameter
Test
Condition Min. Typ. Max.
Unit
F
OSC
PWM Frequency
RI = 26k
60 65 70 KHz
F
OSC-GREEN
Green-mode Frequency
RI = 26k 20
22.5
25
KHz
V
N
FB Pin Threshold for the Beginning of Green
Mode
2.1
V
V
G
Green-OFF Mode Voltage at FB pin
1.6
V
S
G
Slope for Green-Mode Modulation
RI = 26k
85
Hz/mV
F
DV
Frequency Variation Versus VDD Deviation
VDD = 11.5V to 20V
5
%
F
DT
Frequency Variation Versus Temp. Deviation
T
A
= -30 to 85 1.5
5 %
Frequenc
y
V
F
B
F
OSC-GOFF
: 0kHz
V
N
: 2.1V
PWM Frequency
V
G
: 1.6V
S
G
: 85Hz/mV
F
OSC-GREEN
: 22.5kHz
F
OSC
: 65kHz
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