SG3525A Pulse Width Modulator Control Circuit
The SG3525A pulse width modulator control circuit offers
improved performance and lower external parts count when
implemented for controlling all types of switching power supplies.
The on?chip +5.1 V reference is trimmed to
1% and the error
amplifier has an input common?mode voltage range that includes the
reference voltage, thus eliminating the need for external divider
resistors. A sync input to the oscillator enables multiple units to be
slaved or a single unit to be synchronized to an external system clock.
A wide range of deadtime can be programmed by a single resistor
connected between the CT and Discharge pins. This device also
features built?in soft?start circuitry, requiring only an external timing
capacitor. A shutdown pin controls both the soft?start circuitry and the
output stages, providing instantaneous turn off through the PWM latch
with pulsed shutdown, as well as soft?start recycle with longer
shutdown commands. The under voltage lockout inhibits the outputs
and the changing of the soft?start capacitor when VCC is below
nominal. The output stages are totem?pole design capable of sinking
and sourcing in excess of 200 mA. The output stage of the SG3525A
features NOR logic resulting in a low output for an off?state.