SPC5746CBK1AVKU6 temperature testing

[Mizuz]

Hello
I am using SPC5746CBK1AVKU6 microcontroller in a project. We use PLL of microcontroller to achieve 160 MHZ frequency. For the final part under the design, several environmental tests have been defined according to the standard, in which the temperature changes from -40°C to +85°C in 140 cycles with a gradient of 10 degrees per minute, and the part must be fully functional. In another test, the temperature increases from -40 with different time steps to +85 degrees in humidity. In this sample of tests, after reaching the temperature of +85 degrees Celsius and the passage of about 30 to 45 minutes, the microcontroller loses its function and the I/Os related to fail safe are activated.
We are at a critical stage of the project, and since the datasheet of the microcontroller states that the operating temperature is up to +125 degrees, we did not expect to encounter this problem.
Also, I read the things mentioned in this forum and by the way there was a similar register in this microcontroller which was set to 0 by default but we changed it to 2 but the problem was not solved.
Please guide us on what the root of this problem can be, and can we fix this problem by configuring certain registers and pass the desired tests successfully?

[Mizuz]

@petervlna and @KarlP Thank you for your answers.
I checked all HW related events like regulator voltage drop, oscillator mess, etc. and there were no problems. The root of this issue is the clock frequency. According to the investigations we have done, the root of this problem is related to the time when the clock frequency is set to 160 MHZ, that is, the PLL unit is involved. I ask you and NXP company and other knowledgeable and experienced people to guide me how to achieve full performance at 85 degrees "without reducing the clock frequency".

[petervlna]

Hello,

NXP is guaranteeing operation at full speed at 85 degrees.

If you have suspicion that your device is not working according to datasheet please contact your dealer.

Furthermore, take failing the chip from your board and put it into NXP evaluation board. I am pretty sure there will be no issue.

- When it stays at this temperature for more than 30 minutes, it loses its function and the fail safe I/O are activated (the desired I/O is GPIO_N25_PE11, which becomes one when the micro hangs).

Hmm, what should I imagine under this statement? You micro goes into reset and then ends up in some safe state loop? Or watchdog is triggered? What is the operating frequency in this state?

Did you use progressive clock switching?

Best regards,

Peter

[petervlna]

Hello,

the microcontroller loses its function and the I/Os related to fail safe are activated.

Could you explain it closer? Is the device put in reset? Or any faults in FCCU are reported? Are the voltages in defined range when this happen? etc...

Also, I read the things mentioned in this forum and by the way there was a similar register in this microcontroller which was set to 0 by default but we changed it to 2 but the problem was not solved.

I have no idea what you are talking about.

Please guide us on what the root of this problem can be

First make sure you have voltages in specified range when the issue occurs.

Also cross check the errata sheets for your device cut.

Best regards,

Peter

[Mizuz]

Hello @petervlna, Thank you for answering
In the tests I explained, when the temperature reaches +85 degrees:
1- When it stays at this temperature for about 30 minutes, it starts to reset (which is due to the watchdog function).
2- When it stays at this temperature for more than 30 minutes, it loses its function and the fail safe I/O are activated (the desired I/O is GPIO_N25_PE11, which becomes one when the micro hangs).
I read the forum info below and changed the RWSC register from 0 to 3 but to no avail.
https://community.nxp.com/t5/MPC5xxx/Tracing-exceptions-on-MPC5604P/m-p/641887

[petervlna]

Hello,

1- When it stays at this temperature for about 30 minutes, it starts to reset (which is due to the watchdog function).

Ok, so your SW ends up in dead end and SW will trigger reset.

2- When it stays at this temperature for more than 30 minutes, it loses its function and the fail safe I/O are activated (the desired I/O is GPIO_N25_PE11, which becomes one when the micro hangs).

What do you mean by loses it function? I see you refer to safe I/O is set. So the SW is running. Otherwise GPIO will be in High-Z state.

If the issue linked to temperature, then there must be some HW event like voltage drop.

It is hard to guess from limited information on the issue.

Best regards,

Peter

[KarlP]

This sounds similar to an issue I had some time ago albeit on an older MPC55xx.

In the clock configuration I accidentally set one internal stage of the PLL to run outside of a frequency limit given in the datasheet although the final system clock was divided down to the right frequency.

Everything appeared to function normally for a long time until I found clock problems/lock-ups at elevated temperatures.

Once the PLL configuration was corrected (still with the same final fsys) it remained stable at high temperatures.

It may not be your issue at all but maybe worth checking each PLL stage is within the datasheet limits.