One other issues, make sure there is a DC path from V+ input of OpAmp back
to ground, eg. the PWM source must not be AC coupled into the filter input.
That's to insure OpAMP bias current has a return path. No charge slowly accumulates
which would provide an unwanted offset into OpAmp. Also if you choose to use
larger filter Rs, lower Cs, then in V- path to output insert a series R that is ~ the
same the V- sees to ground. To mitigate offset due to bias current flowing thru an
R. If you pick a real low bias current part you should be able to not bother with the
additional R.
Regards, Dana.