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I have limited time to write to external flash in production and going by the typical page program time(0.85ms) is fine, but the maximum page program time(4ms) will not be fast enough.

The question is will all new flash chips be close to the typical time, and the reason for the maximum time is due to chips getting slower over time/cycles, or do all brand new chips vary between the typical and maximum times?

I asked the manufacturer for feedback and they didn't give a straight answer. I am looking at the MX25R3235F part. See page 75 for page program times. https://www.macronix.com/Lists/Datasheet/Attachments/7534/MX25R3235F,%20Wide%20Range,%2032Mb,%20v1.6.pdf

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  • \$\begingroup\$ The worst case is at the highest operating temperature and using the lowest specified programming voltage. If the manufacturer won't give you any information to help you with your highest expected operating temperature and using your actual lowest possible programming voltage, then you are stuck with the specifications. You'll know it will be better if you don't need that worst case situation, but you won't know by how much. You could do a lot of testing. But time is money. Another manufacturer? \$\endgroup\$
    – jonk
    Commented Jul 1, 2020 at 19:03
  • \$\begingroup\$ Do you use the high performance or low power mode? Do you have the high voltage programming supply available for faster programming? Can you change the chip if it fails to perform as fast as needed for the application? Why it was chosen to begin with? Please note that typical times include typical voltage, temperature and data pattern too. Writing mostly ones or mostly zeroes might affect the programming speed as well. Usually chips get slower when programming and erase cycles increase. \$\endgroup\$
    – Justme
    Commented Jul 1, 2020 at 22:02
  • \$\begingroup\$ I am using high performance mode. I am not currently using the high voltage programming supply. If the chip is too slow it cannot be replaced. It is inherited design. \$\endgroup\$
    – Ryan W
    Commented Jul 2, 2020 at 16:09

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The way I understand the flash write process (others please chime in) is that during the write operation,

  1. The flash monitors the charge on the cell (the floating gate),

  2. Detects when that charge reaches a specified level

  3. Continues the write process for some period of time to ensure some margin

Therefore, to some extent, the write time is a statistical process, with the absolute max being the 4 ms specified in the data sheet.

So if you want a robust design, you need to design using the 4 ms worst case number.

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