An integrated circuit (IC) device includes a non-volatile memory device with an array of non-volatile memory cells, and an isolation circuit configured to conduct voltage from an internal voltage supply to one of the memory cells during a hidden write operation to the one of the memory cells, and conduct voltage from an external voltage supply to the one of the memory cells during a non-hidden write operation to the one of the memory cells. Current at the external voltage supply can be monitored external to the IC device during the non-hidden write operation, and current of the internal voltage supply is provided by a capacitor that cannot be monitored external to the IC device during the hidden write operation.