The choice of resistor depends on the cut-off frequency requirement as well as the voltage drop that will occur across that resistor.
A 50ohm resistor and a 0.1uF capacitor is recommended. That should give us a corner frequency of about 33kHz and a small 150mV voltage drop across the filter at 3.3V, so there will be about 3.15V at the VCC pin of the DS1347 which will be fine for the supply.