A power management method includes receiving a first command with first address indicating a first high power operation that is immediately executed in a first memory die, after receipt of the first command, receiving a second command with a second address indicating a second high power operation, such that an immediate execution of the second high power operation would overlap the first high power operation, and delaying execution of second high power operation through a first waiting period that ends upon completion of the first high power operation, while applying a reference voltage to a second word line of the second memory die indicated by the second address.