SG3525 Pulse Width ModulatorThere are numerous Pulse Width Modulation (PWM) controllers available that make the use and application of PWM quite easy. One of the most popular of such controllers is the versatile and ubiquitous SG3525 produced by multiple manufacturers - ST Microelectronics, Fairchild Semiconductors, On Semiconductors, to name a few.
The SG3525A pulse width modulator control circuit offersimproved performance and lower external parts count whenimplemented for controlling all types of switching power supplies.The on1% and the erroramplifier has an input commonmode voltage range that includes thereference voltage, thus eliminating the need for external dividerresistors. A sync input to the oscillator enables multiple units to beslaved or a single unit to be synchronized to an external system clock.A wide range of dead time can be programmed by a single resistorconnected between the CT and Discharge pins. This device alsofeatures builtin softstart circuitry, requiring only an external timingcapacitor. A shutdown pin controls both the softstart circuitry and theoutput stages, providing instantaneous turn off through the PWM latchwith pulsed shutdown, as well as softstart recycle with longershutdown commands. The under voltage lockout inhibits the outputsand the changing of the softstart capacitor when VCC is belownominal. The output stages are totempole design capable of sinkingand sourcing in excess of 200 mA. The output stage of the SG3525Afeatures NOR logic resulting in a low output for an offstate.