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SG6846 — Highly Integrated Green-Mode PWM Controller
November 2008
SG6846
Highly Integrated Green-Mode PWM Controller
Features
Low Startup Current: 8µA
Low Operating Current: 3.7mA
Peak-Current Mode of Operation with Cycle-by-
Cycle Current Limiting
PWM Frequency Continuously Decreasing with
Burst Mode at Light Loads
V
DD
Over-Voltage Protection (OVP)
AC Input Brownout Protection with Hysteresis
Constant Output-Power Limit (Full AC Input Range)
Internal Latch Circuit for OVP, OTP, and OCP
Two-level Over-Current Protection (OCP) with
96ms Delay Time
Very Few External Components
Programmable Over-Temperature Protection (OTP)
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 under-voltage lockout (UVLO)
lower limit. This green-mode function enables power
supplies to meet international power conservation
requirements easily.
The SG6846 is designed especially for switch-mode
power supply (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, OCP is activated such that the SG6846 is totally
shut down. Other protection functions include: AC-input
brownout protection with hysteresis and V
DD
OVP. For
OTP, an external NTC thermistor can be applied to
sense the ambient temperature. When OCP, V
DD
OVP,
or OTP are activated, an internal latch circuit is used to
latch off the controller. The latch resets when the V
DD
supply is removed.
Other features of this controller include built-in
synchronized slope compensation and 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 dual in-line (DIP) and small outline (SOP) packages.
Applications
General-purpose switch-mode power supplies and
flyback power converters, including:
Power Adapters
Open-Frame SMPS
SMPS with Surge-Current Output, such as for
Printers, Scanners, Motor Drivers
Ordering Information
Part
Number
SG6846LSZ
SG6846LSY
SG6846LDZ
SG6846LDY
Operating Temperature
Range
-20 to +85°C
-20 to +85°C
-20 to +85°C
-20 to +85°C
OTP Latch
Yes
Yes
Yes
Yes
Eco Status
RoHS
Green
RoHS
Green
Package
8-Pin SOP
8-Pin SOP
8-Pin DIP
8-Pin DIP
Packing
Method
Tape & Reel
Tape & Reel
Tube
Tube
For Fairchild’s definition of “green” Eco Status, please visit:
http://www.fairchildsemi.com/company/green/rohs_green.html.
© 2008 Fairchild Semiconductor Corporation
SG6846 • Rev. 1.3.1
www.fairchildsemi.com
SG6846 — Highly Integrated Green-Mode PWM Controller
Typical Application
Figure 1. Typical Application
Block Diagram
Figure 2. Block Diagram
© 2008 Fairchild Semiconductor Corporation
SG6846 • Rev. 1.3.1
www.fairchildsemi.com
2
SG6846 — Highly Integrated Green-Mode PWM Controller
Marking Information
F:
L = OTP Latch
SG6846FTP
XXXXXXXXYWWV
T:
D = DIP, S = SOP
P :
Z = Lead Free + ROHS Compatible
Null = Regular Package
XXXXXXXX:
Wafer Lot
Y:
Year;
WW:
Week
V:
Assembly Location
※
Marking for SG6846LSZ (Pb-free)
SG6846LDZ (Pb-free)
Figure 3. Top Mark 1
:
Fairchild logo
Z:
Plant Code
X:
Year Code
Y:
Week Code
TT:
Die Run Code
F:
L = OCP Latch
T:
Package Type (D = DIP, S = SOP)
P:
Y = Green Package
M:
Manufacturing Flow Code
※
Marking for SG6846LSY (Green-compound)
SG6846LDY (Green-compound)
Figure 4. Top Mark 2
© 2008 Fairchild Semiconductor Corporation
SG6846 • Rev. 1.3.1
www.fairchildsemi.com
3
SG6846 — Highly Integrated Green-Mode PWM Controller
Pin Configuration
Figure 5. Pin Configuration
Pin Definitions
Pin #
1
2
Name
GND
FB
Function
Ground
Feedback
Line-Voltage
Detection
Description
Ground.
The signal from the external compensation circuit is fed into this pin. The FB
pin and the current-sense signal from Pin 6 determine the PWM duty cycle.
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 the V
IN
signal. It is suggested to add low-pass
filter to filter out line ripple on bulk capacitor.
A resistor from the RI pin to ground generates a reference current source
inside SG6846. This determines the switching frequency. Increasing the
resistance reduces the switching frequency. Using a 26kΩ resistor RI results in
a 65KHz switching frequency.
For OTP.
An external negative temperature coefficient (NTC) thermistor is
connected from this pin to the GND pin. The impedance of the NTC decreases
at high temperatures. Once the voltage of the RT pin drops below a threshold,
PWM output is disabled.
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, OTP is activated. This two-level
OCP feature is especially suitable for SMPS with surge current output.
Power Supply.
The internal protection circuit disables PWM output in
response to V
DD
over voltage.
The totem-pole output driver for the power MOSFET. A soft driving waveform is
implemented for improved electromagnetic interference (EMI).
3
VIN
4
RI
Reference
Setting
5
RT
Temperature
Detection
6
SENSE
Current Sense
7
8
VDD
GATE
Power Supply
Driver Output
© 2008 Fairchild Semiconductor Corporation
SG6846 • Rev. 1.3.1
www.fairchildsemi.com
4
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