SG6742 Datasheet, PDF (1/14 Pages) Fairchild Semiconductor – Highly Integrated Green-Mode PWM Controller

Highly Integrated Green-Mode PWM Controller
FEATURES
„ High-voltage start-up
„ Low operating current (4mA)
„ Linearly decreasing PWM frequency to 22KHz
„ Frequency jittering to reduce EMI emission
„ Fixed PWM frequency (65KHz)
„ Peak-current-mode control
„ Cycle-by-cycle current limiting
„ Leading-edge blanking
„ Synchronized slope compensation
„ Internal open-loop protection
„ GATE output maximum voltage clamp (18V)
„ V_DD under-voltage lockout (UVLO)
„ V_DD over voltage protection (OVP)
„ Programmable over-temperature protection (RT)
„ Internal latch circuit (OVP, RT)
„ Constant power limit (full AC input range)
„ Internal OTP sensor with hysteresis
APPLICATIONS
General-purpose switch-mode power supplies and
flyback power converters, including:
„ Power Adapters
„ Open-Frame SMPS
DESCRIPTION
The highly integrated SG6742 series of PWM controllers
provides several features to enhance the performance of
flyback converters.
Product Specification
SG6742
To minimize standby power consumption, a proprietary
green-mode function provides off-time modulation to
linearly decrease the switching frequency at light-load
conditions. To avoid acoustic noise problems, the
minimum PWM frequency is set above 22KHz. This
green-mode function enables the power supply to meet
international power conservation requirements. With the
internal high-voltage start-up circuitry, the power loss due
to bleeding resistors is eliminated. To further reduce power
consumption, SG6742 is manufactured using the BiCMOS
process, which allows an operating current of 4mA.
SG6742 integrates a frequency a hopping function that
helps reduce EMI emission of a power supply with
minimum line filters. Also, its built-in synchronized slope
compensation achieves stable peak-current-mode control.
The proprietary internal line compensation ensures
constant output power limit over a wide AC input voltages,
from 90V_AC to 264V_AC.
SG6742 provides many protection functions. In addition
to cycle-by-cycle current limiting, the internal open-loop
protection circuit ensures safety should an open-loop or
output short-circuit failure occur. PWM output is disabled
until V_DD drops below the UVLO lower limit when the
controller starts up again. As long as V_DD exceeds about
26V, the internal OVP circuit is triggered.
SG6742 is available in an 8-pin DIP or SOP package.
TYPICAL APPLICATION
© System General Corp.
Version 1.0.1 (IAO33.0083.B0)
-1-
www.sg.com.tw • www.fairchildsemi.com
September 24, 2007