PAN1740 and SPI communication over temperature?

Our design uses SPI communication between a micro and the PAN1740.  At room temperature, operation is correct.  Once temperature is increased (product shall work up to 55 °C) communication is lost between the micro and PAN1740.  We know this because the product provides indication that this interface is "broken."  Note, the PAN1740 is not advertising or paired when this test starts.  Other SPI parts connected to the micro continue to work.  However, if the PAN1740 is paired at room temperature, temperature increased, operation is correct.  No issues.  What are we missing?  Thank you.

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  • Our design uses SPI communication between a micro and the PAN1740.  At room temperature, operation is correct.  Once temperature is increased (product shall work up to 55 °C) communication is lost between the micro and PAN1740.  We know this because the product provides indication that this interface is "broken."  Note, the PAN1740 is not advertising or paired when this test starts.  Other SPI parts connected to the micro continue to work.  However, if the PAN1740 is paired at room temperature, temperature increased, operation is correct.  No issues.  What are we missing?  Thank you.

    Please let me ask a couple of questions first, so I can get a better understanding of the problem.

    Once temperature is increased (product shall work up to 55 °C) communication is lost between the micro and PAN1740.  We know this because the product provides indication that this interface is "broken."

    So your microcontroller periodically communicates with PAN1740 and when you increase the temperature, this communication does not work correctly any more. Is that understanding correct?

    If so, what happens if you reset your whole system. Does it start up correctly again? If so, how long does it continue to work?

    However, if the PAN1740 is paired at room temperature, temperature increased, operation is correct.  No issues.

    Another clarification. You wrote "if the PAN1740 is paired" - does this mean Bluetooth pairing or pairing to your microcontroller, in the sense of "connection"?

    Does it make a difference if a Bluetooth connection is established for this problem to occur?

    Please note that due to the holiday season answer might be a little bit delayed.

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  • Hello Michael.

    The micro establishes SPI communication with the PAN1740 when the instrument is energized and maintains that in order to have Bluetooth operation available when requested by the user.  Our firmware will present an indication if at some point the micro looses communication with the PAN1740.

    I have not attempted the experiment you described above - a reset (power off/on) at elevated temperature.  However, if we let a unit get back to room temperature, resetting (off/on) usually normal operation occurs.  

    When I state pairing that is between the instrument, the PAN1740, and another Bluetooth device, as a phone, for example.  Hence, if the instrument is paired, the radio is working, there is no problem.

    We (actually our very excellent software engineer) did an experiment where he establishes SPI communication between the micro and PAN1740.  He then makes certain the radio portion is on.  The instrument is not advertising, not searching for another device to pair.  This works fine.  SPI communication is not lost.  I don't know if that is a hint.

    Although this firmware change fixes the problem, we will have an increase in operating current with the radio turned on continuously.

    Thank you.

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