Issue about the MC9S12XEP100 CLOCK Circuit

[dingding1]

I am using the CPU MC9S12XEP100,and using CMOS Compatible External Oscillator.

The original circuit is as follows：

some products(About 0.2% of the total, so far) occur the phenomenon of abnormal work after about two years used.

after that I realized that maximum oscillator voltage can be Vddpll+0.3V(2.16V).

so I plan to change the crystal oscillator circuit (using LDO to reduce the crystal oscillator power supply to 1.8V and replace it with a 1.8V crystal oscillator).

My question is：whether the original product (which used to use 5V power supply, but currently has no faults) can maintain stable long-term operation after replacing the crystal oscillator circuit(with 1.8V power supply)? Is there still a possibility of premature failure?

Looking forward to your reply.thanks a lot!

[dingding1]

Hi,We attempted to operate the MCU(which used a 5V powered crystal oscillator,and PLL cannot function properly) by setting the MCU frequency to 8M (without using PLL), and the MCU was able to operate normally. My question is: 1. Will this failure mode only damage the internal circuit of the phase-locked loop and not affect other parts. 2. For MCUs that have been in use for a period of time (using 5V power supply for crystal oscillators that exceed specifications) but still work normally, if the crystal oscillator circuit is changed to 1.8V power supply and the MCU frequency is adjusted to 8M (not applicable to PLL frequency doubling), can this ensure long-term MCU performance

best regards 

[lama]

Hi,

No, it cannot be done without destructive analysis. Each device may also respond differently to conditions outside the operating range, so it is not possible to generalize the results to other microcontrollers based on a single test.

Moreover, we have met with issues related to this phenomenon in past. It is really ticking a time bomb with setup we do not know.

Best regards,

Ladislav

[dingding1]

Hi Iama,thank you very much for your reply.I understand what you mean. If EXTAL is used beyond the specified range, it will cause certain damage to the internal of the MCU. Is there a way to evaluate the degree of damage to the MCU through testing to determine whether it needs to be replaced.

Best regaids

[lama]

Hi,
Be sure your clock, if you use external canned oscillator, fits operating conditions and its max value is in the range <0.7Vddpll;Vddpll+0.3> where Vddpll nominal value is 1.8V. Otherwise electromigration effect can damage oscillator circuitry in not defined time.
If the MCU was working outside of the operating conditions, then there is no guarantee of behavior even if you start using the correct conditions.

So, if you used the EXTAL pin within conditions then there is no problem to change oscillator. The design example you can find at
https://community.nxp.com/t5/S12-MagniV-Microcontrollers/Reference-schematics-for-S12-X-devices/ta-p...

Best regards,
Ladislav

[dingding1]

Hi Iama. thank you very much for you reply.I understand your point: If EXTAL is used beyond the specified range, it will cause certain damage to the internal of the MCU. So is there any way to evaluate the degree of damage to the MCU through testing to determine whether it needs to be replaced.

best regards