SG6846A Datasheet, PDF (1/13 Pages) Fairchild Semiconductor – Highly Integrated Green-Mode PWM Controller

Highly Integrated Green-Mode PWM Controller
FEATURES
ƒ Two-level OCP with 1700ms delay time
ƒ Output short-circuited delay time: 100ms
ƒ Low start-up current (8µA)
ƒ Low operating current (3.7mA)
ƒ Peak-current mode operation with cycle-by-cycle
current limiting
ƒ Programmable PWM frequency with frequency
hopping
ƒ PWM frequency continuously decreasing with burst
mode at light loads
ƒ V_DD over-voltage protection (OVP)
ƒ AC input brownout protection with hysteresis and
constant output power limit
ƒ Constant output power limit (full AC input range)
ƒ Internal latch circuit for OVP, OTP, and OCP
ƒ Built-in soft-start
ƒ Open-loop protection with 1700ms delay time
APPLICATIONS
General-purpose switch-mode power supplies and
flyback power converters, including:
ƒ Power adapters
ƒ Open-frame SMPS
ƒ Specifically fit for SMPS with surge-current output
(such as for printers, scanners, motor drivers, etc.)
DESCRIPTION
The highly integrated SG6846A series of PWM
controllers provides features to enhance the performance
of flyback converters. To minimize standby power
Product Specification
SG6846A
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.
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 and the SG6846A latches off.
If the switching current is higher than two thirds the
peak-current threshold for 100ms and the voltage on the
VDD pin is higher than V_DD-OFF + 1V, the PWM pulses
are latched off immediately once V_DD voltage is lower
than V_DD-OFF + 1V; useful if an output short-circuit occurs.
SG6846A also integrates a frequency hopping function
that reduces 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 a 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 reduce stress on the
MOSFET and start-up 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 are activated, an internal latch circuit is used to
latch-off the controller. The PWM pulses stay latched off
until the power supply is unplugged from the main outlet.
SG6846A is available in an 8-pin SOP package.
TYPICAL APPLICATION
© System General Corp.
Version 1.1.1 (IAO33.0059.B1)
-1-
www.sg.com.tw • www.fairchildsemi.com
September 26, 2007