As mentioned, the P-P voltage should stay the same.
Video shown below is from the PWM routine of:
pwmout C.2,99,400 'start PWM on Port C Pin 2 @ 100%
for w1 = 0 to 400 ' pwmduty needs a (W)ord var, not a (B)yte var
pwmduty C.2, w1 'adjust PWM Duty from 0% to 100%