1 Why External on-PCB Flash?

MCU memory needs and CPU performance levels requirements are continuously increasing. MCU industry product roadmaps with up to 5K DMIPs and 64MB of on-chip flash are common, but it is well understood that embedded flash technologies are not expected to scale beyond 22 nm due to the high voltage (HV) gate oxide-based transistors required for programing and erasing flash bits. For example, on 28nm, 18 additional masks or reticles are required (vs. the CMOS only process technology).^{1, 2.}

In comparison, typical 8MB Octal Serial Peripheral Interface (OSPI) flash can vary in cost from ~$0.50 - ~0.80. Figure 1-1 shows the AM263P CPU + TCM architecture with the flash sub-system (FSS) that includes OptiFlash.

The additional cost of embedded flash technology results in either high-cost MCUs or architectures that reduce the amount of OCSRAM to achieve a specific cost point.

Since OCSRAM or TCM is always required for highly deterministic, low latency applications (such as real-time control), MCU architectures with a larger OCSRAM to Flash ration perform better. For example, the AM263P TCM has an access time of 2.5 ns and OCSRAM worst-case accesses can vary between 60 ns-90 ns.

Finally, alternative non-volatile memory (NVM) technologies such as, phase-change SRAM (PC-SRAM) or magnetic RAM (MRAM), are not yet ready for use in volume production of high reliability, low defective parts per million (DPPM) applications such as automotive and industrial.