Separate peak current checkpoints for closed and open block read icc countermeasures in nand memory

Abstract

To reduce spikes in the current used during read operations by a system of multiple NAND memory dies operated in parallel, relative delays between the memory dies are introduced before high current sub-operations of the read. The occurrence of the primary current peak in the read operation can depend upon the extent to which a selected memory block is programmed. For example, in a closed block the primary peak occurs when ramping up unselected word lines, while for an open block the primary read peak occurs when the bit lines are charged up. To account for these differences, determining where to introduce relative delays is based on the extent to which a block is programmed. For example, if a block fully or largely closed, delays are introduced before ramping up the unselected word lines, but otherwise adding the delays before charging up bit lines.