Find AN899! The output signal form the controller has pulse shape. After that there are 2 options. First directly passing this pulses to the power circuit. Your load (if it`s inductive) will "transform" this pulses to something near to sinusoidal voltage. If your load is not inductive it`s a good idea to use output pulse transformer or output filter.
Second way is to use a triangular voltage and the signal on your power circuit to be a sum of both(and again the load will make the changes if it`s inductive).
You must know the register that holds the value of the output frequency and this with the duty cycle are different. This with the duty cycle is 4 times bigger. This means if you load 200 for frequency the max value for duty cycle is 800.
Stoyanoff