SG6846A — Highly Integrated Green-Mode PWM Controller
September 2008
SG6846A
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 OCP Delay: 1600ms
Output Short-Circuited Delay Time: 100ms
Programmable PWM Frequency with
Frequency Hopping
OCP Threshold is Half Peak Current Limit
Feedback Open-loop Protection with 1700ms Delay
Built-in Soft-Start
Description
The SG6846A is especially designed for SMPS with
surge-current output, incorporated with a two-level OCP
function. Besides the cycle-by-cycle current limiting, if
the switching current is higher than two thirds the peak-
current threshold for 1700ms, over-current protection is
activated such that the SG6846A is latched off.
If the switching current is higher than two thirds of the
peak-current threshold for 100ms, and the voltage on
the V
DD
is still higher than V
DD-OFF
+ 1V, the PWM
pulses are latched off immediately once the V
DD
voltage
is lower than V
DD-OFF
+ 1V. This is useful when an
output short circuit occurs.
SG6846A also integrates a frequency-hopping function
internally to reduce EMI emission of a power supply
with minimum line filters. Its built-in synchronized slope
compensation
provides
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. Internal soft-start is built-in to
soften the stress on the MOSFET and startup current
during power on period.
Other protection functions include AC input brownout
protection with hysteresis, V
DD
over-voltage protection,
and over-temperature protection. For over-temperature
protection, an external NTC thermistor can be applied to
sense the ambient temperature. When OCP, V
DD
OVP,
or OTP is activated, an internal latch circuit latches off
the controller. The PWM pulses stay latched off until the
power supply is disconnected from the mains outlet.
SG6846A controller 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
SG6846ALSY
SG6846ACSY
SG6846ALSZ
Operating
Temperature Range
-40 to +105°C
-40 to +105°C
-40 to +105°C
OCP
Latch
Yes
No
Yes
Eco
Status
Green
Green
RoHS
Package
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
For Fairchild’s definition of “green” Eco Status, please visit:
http://www.fairchildsemi.com/company/green/rohs_green.html.
© 2008 Fairchild Semiconductor Corporation
SG6846A • Rev. 1.1.4
www.fairchildsemi.com
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
