About the LPO trimming

[Hirofumi]

Is LPO trimming by LPOTRIM disabled in VLPS mode?

I also referenced the thread below.
I used the RTC that clock source is LPO and measured the 1 hour in RUN mode only,
The result was within the range calculated at 128KHz ± 1.5kHz of LPO.
This timer tolerance was within my expected.

But When I measured the 1 hour using RTC while switching RUN mode and VLPS mode by LPTMR interrupt,
The result of margin of error was more larger.
So, I think the function LPO trimming is disabled in VLPS mode.
Is my understanding correct?

[danielmartynek]

Hello @Hirofumi,

The trimming is not disabled.

What is the trim value for that particular MCU?

And what is the difference in the frequency.

By the way, the LPO frequency can be measured at CLKOUT.

BR, Daniel

[Hirofumi]

Hi, daniel.
Thank you for supporting.
I read LPOTRIM register and the value is 0x1B.
I could confirm LPO frequency using CLKOUT.
And LPO frequency was 128.8kHz in VLPS and RUN mode.
When LPO Clock is 128+-1.5kHz, my understand that the RTC timer tolerance is +-1.17%
But I measured result timer error was +2% when I used switching VLPS and RUN mode.
Do you have anything idea why this phenomenon is occur?

[danielmartynek]

Hi @Hirofumi,

Without the trimming the LPO frequency would be much higher, +15kHz if I'm not mistaken.

The LPO is trimmed close to the typ. 128kHz.

But since one step gives ~3kHz difference, it can be trimmed to around 128kHz +-1.5kHz in the factory.

But this is just the trimming.

It does not mean the tolerance of the RTC clocked by the LPO is +-1.5kHz.

There are other factors that impact the LPO like operational conditions, aging, etc.

Regards,

Daniel

[jingfang]

My custom test frequency under 113HZ,when LPOTRIM = 0,changing the value of the LPO can change the frequency.Is there somewhere I can check?

[Hirofumi]

Hi,Daniel.
Thank you for supporting.
I referred s32k datasheet.
The S32K1xx LPO frequency has the following specifications:
Min. 113kHz, Typ. 128kHz, Max 139 kHz

Should I consider that the tolerance of the RTC clocked by the LPO(typ-15kHz) even if the trimming is enable.
Because there are some factors that impact LPO.
Is my understanding correct?

[danielmartynek]

Hello @Hirofumi,

The LPO is very imprecise. The LPO specification (Min. 113kHz, Typ. 128kHz, Max 139 kHz) applies only with the trim value obtained during the production which trims the LPO as close to 128kHz as possible.

By trimming the LPO with a custom trim value, we can easily get out of the specified range.

Regards,

Daniel

[Hirofumi · Accepted solution]

Hi daniel.

Thank you for information. I got it.

[jingfang]

If no change LPO trimming, measured data <113KHZ, whether this can be used normally?

[danielmartynek]

What is the trim value when LPO freq < 113kHz?

You should see a frequency within the specified range when the NXP trim value is used.

Thanks,

BR, Daniel

[jingfang]

the trim value is default = 0,that's why it's so weird.

[danielmartynek]

Hello @jingfang,

Is the LPOTRIM equal to 0b00000 by default out of reset?

If so, can you post the maskset number of the chip?

It is printed on the package.

BR, Daniel

[jingfang]

Yes, the trap values are as follows:  Do you mean lot number? Lot number is:0B204X.

[danielmartynek]

Can you share all the labels on the package?

Thank you,

BR, Daniel

[jingfang]

Yes~