My customer would like to confirm about the absolute maximum input voltage rating of SD terminal of SSM2305. Is it 0V to +Vdd range?
Yes, 0V to +VDD is a good range to keep it within. Generally, you would not want to apply more than VDD+0.3V to this pin. I would try not to push this spec. If you have a decent series impedance then the currents will be limited so that will help to protect the part should you go above VDD but even with a high series impedance you do not want to go above VDD +0.3V.