Okay, OP, could you tell us clearly what you fundamentally want to do, rather than just saying "PWM DAC"? This relies on the assumption that both you and we are using and understanding the right terminology appropriately.
When I hear "PWM DAC" the first thing that comes to mind is converting a digital PWM signal from a uC into a programmable analog waveform, using filtering, amplification and offset etc.
But then you're talking about triangle waves and comparators - that's the sort of system you'd use to convert an analog variable voltage into a digital PWM signal, without necessarily using any microcontroller at all.