"my clock speed is 22MHz, the slowest PWM I can produce is 168Hz."

I see. You are right. I didn't calculate it before. You really cannot generate 50Hz on a PWM output directly. In your case is one chance for your 80C552 PWM. It's SW/HW solution. Set 200Hz (200.64Hz or 199.71Hz) and use HW divider by 4 (one HC74 package) to get 50Hz.

If you can't use such way there is possibility to use Timer 2 and its compare logic. Time is sufficient and there is possibility to generate both time slopes, maybe ->(waveforms dependance.?.). There is also useful to employ HW reset of Timer 2.

Vaclav