PWM CONTROLLER IC 3525

The function of each pin of the IC3525A:
Pin 1: It takes the reference input and compares it with the feed back.
Pin 2: It takes the feedback from the output and compares it with the reference input.
Pin 3: This pin is not used in the circuit it is used to cascade this pin with other devices.
ØPin 4: OSC output is used to get an oscillator frequency.
Pin 5 and Pin 6: There are used to select the operating frequency of the whole circuit.
Pin no 7: This is the discharge pin and it is used to set the delay between the pulses.
Pin no 8: This is the soft start pin and it allows the device to start slowly and gradually.
Pin no 9: This pin provides closed loop frequency compensation to the circuit.
Pin no 10: This is the shutdown pin and it pulls the IC to shutdown in case of hazardous
circumstances.
Pin no 11 and 14: They provide the output from the IC in the form of the pulses.
Pin no 12 and 15: This is supply and ground pin of I.C.
Pin no 16: It provides the reference voltage for the pin no 2.

The SG3525A, 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 dead time 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.

Features of 3525A
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 Dead time Control
Input Under voltage Lockout
Latching PWM to Prevent Multiple Pulses
Pulse–by–Pulse Shutdown
Dual Source/Sink Outputs: ±400 mA Peak