Hi @Ensaf,
I provide information here as well for consistancy.
I think there is no conflicting information, but misinterpretation of the data provided in the datasheet and by NXP engineers.
So let’s restart all together here
First of all, I like the schema you have shared here:

From NXP DS, this is exactly what data tells us
There is another element to consider on the data provided in the DS.
- On all the flash sector except the last 256kB one, the minimum guaranteed endurance is 10K cycles.
- On the last flash 256kB sector, the minimum guaranteed endurance is 100K cycles
This is an important information to guide you to use the last 256kB flash sector to store non-volatile data.
Now, from your schema, you have drowned the Valeo’s expectations.
You want 15 years of data retention with data integrity.
What really counts here is the following:
- How many cycles your system can do per year/per month/per day before reaching 100K cycles in 15 years?
- How many cycles your system can do per year/per month/per day to respect the data retention of 15 years if the keyfob/car anchor stops working?
To provide the answer to question 1:
- 100K cycles = 15 years (that’s your target)
- X K cycles for 1 year?
- X = 100K / 15 = 6.666K cycles/year
- X = 6666K cycles / 12 = 555 cycles/month
- X = 555 cycles / 31 = 17.92 cycles/day
If you perform less than ~18 Program/Erase cycle per day, you will guarantee the data integrity for 15 years, located in the last 256kB of Flash.
To provide the answer to question 2: Let’s take the 6,666K cycles/year obtained above as an example.
- Year 1: If 6,6666K cycles is performed over the year and the system stops, the minimum the datasheet can guarantee for data retention à 6,666K < 10K = 10 years + 1 year of operation = 11 years. This doesn’t satisfy the 15-years target.
- Year 2: If 6,666K cycles * 2 = 13,332K cycles is performed over the 2 past years and the system stops, the minimum the datasheet can guarantee for data retention à 13,332K < 100K = 5 years + 2 year of operation = 7 years. This doesn’t satisfy the 15-years target.
We clearly see the data retention as an important factor for the product lifetime.
Key principle
At any stopping point: Operation time + retention(min @ cycles) ≥ 15 years
Recommended cumulative cycle limits
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Product Age (years)
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Max Cumulative Cycles
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Min Retention @ this level
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Guaranteed Total Lifetime
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Status
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0 → 5
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≤ 1k cycles
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≥ 20 years
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≥ 20 + t ≥ 25 years
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Safe margin
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5 → 10
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≤ 10k cycles
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≥ 10 years
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≥ 10 + t ≥ 15–20 years
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Safe
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10 → 15
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≤ 100k cycles
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≥ 5 years
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≥ 5 + t ≥ 15–20 years
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Safe
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> 15
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Not applicable
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Not required
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Requirement already met
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—
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This gives us theoretical cycles/year as below:
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Time Range
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Allowed Cycles in Period
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Avg Cycles / Year
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Avg Cycles / Day
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0 → 5 yrs
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0 → 1k
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≤ 200 / year
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~0.55 / day
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|
5 → 10 yrs
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1k → 10k
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≤ 1.8k / year
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~5 / day
|
|
10 → 15 yrs
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10k → 100k
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≤ 18k / year
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~50 / day
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This is strictly what the KW45 datasheet can guarantee at minimum.
You can assume we have a linear degradation of the data retention per cycles between:
- 1K (20 years data retention) à 10K (10 years data retention): each 1K cycle removes 1 year of data retention
- 10K (10 years data retention) à 100K (5 years data retention): each 10K cycles removes 0.5 years of data retention
But this is just assumptions and NXP cannot guarantee this data. Taking this assumption into account would make the number of cycles/year more flexible.
This is why the above tables are what NXP can guarantee for 15 years operation.
For robustness in your design:
- Implement:
- Highlight:
- The last 256kB block only improves endurance (100k)
- It does NOT improve retention curve (same retention vs cycles relationship applies)
I hope this is now clear to you
Please let me know if you need additional details or if any points require clarification.
Regards,
Alex