GENERAL DESCRIPTION
OB2278 is a highly integrated current mode PWM
control IC optimized for high performance, low
standby power and cost effective offline flyback
converter applications.
PWM switching frequency at normal operation is
externally programmable and trimmed to tight
range. At no load or light load condition, the IC
operates in extended ‘burst mode’ to minimize
switching loss. Lower standby power and higher
conversion efficiency is thus achieved.
VDD low startup current and low operating current
contribute to a reliable power on startup design
with OB2278. A large value resistor could thus be
used in the startup circuit for reduced power loss.
The internal slope compensation improves system
large signal stability and reduces the possible
sub-harmonic oscillation at high PWM duty cycle
output. Leading-edge blanking on current sense
input removes the signal glitch due to snubber
circuit diode reverse recovery and greatly reduces
the external component count and system cost in
the design.
OB2278 offers comprehensive protection
coverage including Cycle-by-Cycle current
limiting(OCP),
VDD
Under
Voltage
Lockout(UVLO),
VDD
Over
Voltage
Protection(OVP), VDD Clamp, Gate Clamp, Over
Load protection(OLP) and Over Temperature
protection (OTP), etc.
Different latch shutdown options are offered on
OB2278 in different device version. T version
supports both OVP and OTP latch shutdown. L
version provides all OVP, OTP and OLP latch
shutdown control.
Excellent EMI performance is achieved with soft
switching control at the totem pole gate drive
output.
OB2278 is offered in SOP-8 and DIP-8 packages.
TYPICAL APPLICATION
OB2278
Current Mode PWM ControllerLatch Shutdown
Product Specification
FEATURES
■ Power On Soft Start
■ Extended Burst Mode Control For Improved
Efficiency and Minimum Standby Power
Design
■ Audio Noise Free Operation
■ External Programmable PWM Switching
Frequency
■ Internal Synchronized Slope Compensation
■ Low VIN/VDD Startup Current(3uA) and Low
Operating Current (2.3mA)
■ Leading Edge Blanking on Current Sense
Input
■ Complete Protection Coverage with selective
protections for Latch Shutdown
o VDD Over Voltage Protection(OVP) – Latch
Shutdown
o Over Temperature Protection(OTP) – Latch
Shutdown
o Over Load Protection. (OLP) – Auto
recovery or Latch Shutdown
o VDD Under Voltage Lockout with Hysteresis
(UVLO)
o Gate Output Voltage Clamp (16.5V)
o Built-in OCP Compensation to Achieve
Minimum OPP Variation over Universal AC
Input Range.
APPLICATIONS
Offline AC/DC flyback converter for
■ Adaptor
■ Notebook Adaptor
■ LCD Monitor/TV/PC/Set-Top Box Power
Supplies
■ Open-frame SMPS
■ Printer Power
©On-Bright Electronics
Confidential
-1-
Datasheet
OB_DOC_DS_2278A2
