SG6846B — Highly Integrated Green-Mode PWM Controller
October 2008
SG6846B
Highly Integrated Green-Mode PWM Controller
Features
Low Startup Current: 8µA
Low Operating Current: 3.7mA
Peak-Current Mode 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
(BLSY, BLSZ)
Two-level OCP Delay with 200ms
Programmable PWM Frequency with Frequency
Hopping
OCP Threshold is 2/3 Peak Current Limit
Soft Startup Time: 5ms
Description
The highly integrated PWM controller, SG6846B,
provides several features to enhance the performance
of fly-back 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. If
V
FB
is larger than around 1.6V, PWM pulses out. This
green-mode function enables power supplies to meet
international power conservation requirements.
The SG6846B is 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 OCP threshold and
lasts for 200ms, SG6846B stops gate immediately and
latches itself (BLSY version) or restarts after V
DD
charges up to 16.5V (BCSY version). SG6846B also
integrates frequency-hopping function internally. The
frequency hopping function helps reduce EMI emission
of a power supply with minimum line filters. It has built-
in synchronized slope compensation, proprietary
internal compensation for constant output power limit
over universal AC input range. The gate output is
clamped at 18V to protect the external MOSFET from
over-voltage damage.
Protection include: AC input brownout protection with
hysteresis and V
DD
over-voltage protection. For over-
temperature protection, 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 V
DD
supply is removed.
SG6846B is available in 8-pin SOP package.
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
SG6846BLSY
SG6846BLSZ
SG6846BCSY
SG6846BCSZ
Operating
Temperature Range
-40 to +105°C
-40 to +105°C
-40 to +105°C
-40 to +105°C
OCP
Latch
Yes
Yes
No
No
Eco
Status
Green
RoHS
Green
RoHS
Package
8-Pin Small Outline Package (SOP)
8-Pin Small Outline Package (SOP)
8-Pin Small Outline Package (SOP)
8-Pin Small Outline Package (SOP)
Packing
Method
Tape & Reel
Tape & Reel
Tape & Reel
Tape & Reel
For Fairchild’s definition of “green” Eco Status, please visit:
http://www.fairchildsemi.com/company/green/rohs_green.html.
© 2008 Fairchild Semiconductor Corporation
SG6846B • Rev. 1.3.3
www.fairchildsemi.com
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
