Pulse Width Modulator Control Circuits

The SG3525A, SG3527A pulse width modulator control circuits offer 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. These devices also feature 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 while the SG3527A utilized OR logic which gives a high output when off.

• 8.0 V to 35 V Operation

• 5.1 V ± 1.0 Trimmed Reference

• 100 Hz to 400 kHz Oscillator Range

• Separate Oscillator Sync Pin

• Adjustable Deadtime Control

• Input Undervoltage Lockout

• Latching PWM to Prevent Multiple Pulses

• Pulse–by–Pulse Shutdown

• Dual Source/Sink Outputs: ±400 mA Peak