CURRENT MODE PWM CONTROLLER FOR FORWARD AND FLYBACK APPLICATIONS

DESCRIPTION

The UTC UC3853A is a high performance current mode PWM

controller ideally suited for low standby power. Low V DD startup

current make the power reliable on startup design and a large

value resistor could be used to minimize the standby power. At no

load condition, the IC operates in power-saving mode for lower

standby power, decreasing frequency for Higher conversion

efficiency at light load condition. It contains protection with

automatic recovery including OLP, OCP, VCC OVP, BNO and

OTP. To protect the power MOSFET, Gate-drive output is fixed up

to 15V max.

Excellent EMI performance is achieved with UTC proprietary

frequency hopping technique (ZL201020615247.1) together with

soft driver control. The controller offers everything needed to build

cost−effective and reliable ac−dc switching supplies dedicated to

ATX power supplies. Finally a SOP-8 package saves PCB space

and represents a solution of choice in cost sensitive project.

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FEATURES

* Peak Current Mode Control

* Adjustable Switching Frequency

* Adjustable Soft−start Timer

* Adjustable Internal Ramp Compensation

* Jittering Frequency ±6% of the Switching Frequency

* Power-saving mode for high standby efficiency

* Auto−recovery Primary OCP with 10ms Fixed Delay

* Auto−recovery Brown−Out Detection

* Delayed Operation Upon Start−up via an Internal Fixed Timer

* UC384X−like UVLO Thresholds

* V CC from 9V to 28V with Auto−recovery UVLO

* Internal 350ns Leading Edge Blanking

* Gate output voltage clamped at 15V

* UC3853A: Maximum 47% Duty Cycle

* UC3853B: Maximum 75% Duty Cycle