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KE02: Internal Clock Source: IRC in FEI Mode: Impact of Maximum Frequency

Question asked by Colin Campbell on Nov 5, 2019
Latest reply on Nov 10, 2019 by Colin Campbell



Our MKE02Z64VFM4 clock configuration uses the Internal Reference Clock (IRC) in FEI Mode, with the the IRC to 39.0625 kHz and the FLL Multiplier set to 1024, to obtain a nominal maximum clock frequency of 40 MHz. We have not undertaken additional trimming of the Internal Clock Source, and are therefore reliant on the accuracy of the production trimming (+/- 0.5%).


In our application, we have seen repeatable resets of the CPU when the case temperature of the CPU is >= 100C. We have inspected the CPU SIM_SRSI Reset Source Register and confirmed that the source of the reset is the internal Watchdog.


Our reading of section 20.4.5 of the KE02 Family Reference Manual suggests that this behaviour is probably due to our core clock frequency exceeding the maximum allowable value of 40 MHz (noting the IRC Trim accuracy of +/- 0.5%), which is then followed by a Firmware lockup state with a subsequent assertion of the Watchdog and CPU reset – could you please provide a response to the following questions:


  1. What is the expected system behaviour when the maximum core clock frequency is exceeded?
  2. Are there any known limitations/errata that have been published for operation of the KE02 devices at high temperatures and (Tcase >= 100C) and at high clock frequencies (e.g. 40 MHz)?


Thank you for the assistance - CC