Hi,
For an RC low pass filter excited by a pulse input wave after a time t more than 5 RC time constants the ripple voltage peak to peak is:
Vpp=Vs*(e^(a*t)-1)*(e^(a*T)-1)/(e^(a*T+a*t)-1)
where
a=R*C
t=pulse time high (where pulse amplitude is equal to Vs)
T=pulse time low (where pulse amplitude is equal to 0 volts)
Vs=charging source voltage
e=2.71828...
and the response time is 4 to 5 RC time constants depending on required accuracy.
Example:
Vs=5,R=1, C=1,t=0.1,T=0.2
so:
a=R*C=1
Vpp=0.3328 to four significant figures.