What should be the voltage rating of C1 and C2 capacitors of MAX3227EAE
Referring to the application schematic in the MAX3227EAE datasheet; the internal power supply consists of a regulated dual charge pump that provides output voltages of +5.5V (doubling charge pump) and -5.5V (inverting charge pump), over the +3.0V to +5.5V range. C1 and C2 are flying capacitors and they must be rated for at least the Vinmax. C3 and C4 are reservoir capacitors and they must be at least rated for twice the Vin. In both cases it is recommended to leave some voltage headroom for transients. 16V rating stress will be sufficient for all the capacitors. However, take DC biasing of capacitance values in to consideration if you are using ceramics.