Using IR21531 as a simple 1 channel gate driver
You won't be able to use the IR21531 the way you desired. This device does not accept an input signal (other than Shutdown) where you can directly control the gating rate and duration of gate pulse.

You said you want to use a 3.3v PWM signal to drive your FET (MOSFET). 
Search on the internet or in stores for a Low Side Driver.  Even here on EE Stack Exchange there are many answers when searching for drivers and low side drivers.

Exixsting questions that may help you: 


Help understanding Low side N-Channel MOSFET driver circuit   
MOSFET Driver Failure




Another solution would be to use a gate driver like MIC5019 that includes internal charge pump to convert 3.3V into 10V.