Go through the SG3525 datasheet. The resistor between Rt(pin 6) and ground, and the capacitor between Ct(pin 5) and ground set the frequency. Resistor between Rd (pin 7) and Ct (pin 5) sets deadtime. The relationship between these and frequency is given in the datasheet. To shutdown the SG3525, you can pull pin 8 to ground or pull pin 10 high. Both of these are also shown in the datasheet.
Here's the datasheet:
SG3525 (ON SEMI):
www.onsemi.com/pub/Collateral/SG3525A-D.PDF