LC filter sizing 50Hz AC to good DC (RMS to DC)
With RMS to DC conversion you will get ripple because (using traditional methods) the waveform is squared mathematically, then averaged then the square root is taken. It's the averaging process that is the weak link in the process and I guess it will be on this chip despite it using a sigma delta approach. The spec sheets recommends this for ripple reduction: -



If you can't use op-amps and you don't want to live with a long latency, maybe doing something in code will work. There are some clever filters that can be implemented or maybe you can just look for max and min and take the average of those values? Another idea might be to synchronize to the incoming AC so that you always take a reading at a repeatable point and hence this should give you a stable point in the RMS output?

By the way you'd need a big inductor to get anywhere near what the op-amp circuits can do. 1H (not uH) and 10uF will give you a 2nd order cut-off of 50Hz and your ripple (100Hz) will still be hardly affected - you'd be looking for something like a 10Hz LPF and that would need 25H and 10uF - an op-amp is easier.