During power-up or power-down VCC must always be greater than or equal to VIO (VCC >= VIO). Iam attaching the datasgeet link also. Please refer to page 66 and 67 for further reference and power sequencing.
Thanks and Regards,
So in that case I can give Vcc (Core Voltage 3.3V) always and then give Vio (1.8V) . Is my understanding correct??
Yes, you can do that. Your understanding is correct.