True RMS-to-DC converter with AD736
You have possibly made an error reading the data sheet - it needs proper + and - supplies with a much "harder" 0V feeding the common pin. You are using 100 k resistors and these are unacceptably large without decouplers across each: -



Also note what the DS says about minimum supply voltage: -


  while operating from the minimum power supply voltage of +2.8 V, –3.2
  V


That's a total of 6V minimum (when I went to school) so, your 5V supply is too low. For a symmetrical supply I'd be looking at +/- 3.3V to be on the safe side.

You also have Cav connected to a node with an earth symbol - it's unclear where this fits in with the rest of the circuit.

I'm not ruling out other errors but these seem the obvious.