Endurance and retention flash controller with programmable binary-levels-per-cell bits identifying pages or blocks as having triple, multi, or single-level flash-memory cells

Abstract

An retention flash controller reads assigned-level bits from a bad block/erase count table or from a page status table that indicate when flash memory cells operate as Triple-Level-Cell (TLC), Multi-Level-Cell (MLC), or Single-Level-Cell (SLC). Pages that fail as TLC or MLC are downgraded for use as SLC pages by changing the assigned-level bits. The level bits adjust truth tables used by translation logic that receives inputs from voltage comparators reading a bit line. The range of voltages for each logic level may be adjusted by the truth tables or by programmable registers. The programming voltage or programming pulses may be adjusted to increase endurance and the number of permitted program-erase cycles while reducing retention times before a refresh is needed of the flash cells. Mixed configurations of flash memory have MLC blocks and MLC as SLC blocks, or other combinations.