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TCA9535: Operation Issue at -40C

Richard Elmquist
Mastermind 45250 points
Part Number: TCA9535

My have a military customer who is having an issue with the TCA9535TWR at -40C. Here is a description of what the customer is seeing:

I performed some tests with a known good board as well as a problem board. Our configuration uses a TI MSP430x2xx micro controller communicating with the TCA9535TWR I2C expander on the I2C bus. Our software waits 10 msec after power on before attempting communication with the I2C expander. After the 10 msec delay, the microcontroller looks at the UCBBUSY bit on the UCB0STAT register to determine if the I2C bus is busy or idle prior to attempting to access the I2C expander.

For the known good board, 10 msec is enough delay after power up for the I2C bus to come back as idle at both room temperature (25 degrees C), and at -40 degrees C. For the problem board, 10 msec is sufficient at room temperature for the bus to come back as idle, but at -40 degrees C, we had to increase the delay to 100 sec in order for the bus tom come back as idle.

The delay in the bus becoming active seems to be excessive to me. Have you seen this issue before?

Do you need to see any of the design details or layout? It might be difficult to get this considering that this is military customer, but I can try.

Please let me know if you have any further questions.

Richard Elmquist

  • 0
    TI__Mastermind 23116 points
    Hello Richard,
    Can they reproduce this with more than one part or more than one board? We need to make sure this is the part and not some other issue on the board. Have they seen at what temp they begin to see the problem?
    -Francis Houde
  • 0 in reply to fhoude
    TI__Mastermind 45250 points

    Francis,

    I have asked this question concerning the number of boards involved and will post the response once I receive it.

    It appears that the suspect board(s) only begin to show the issue at their lowest testing level, so I am not sure if the issue can be seen at a higher temp. I can ask them this question and I will post their response.

    Is the time frame that they are seing indicate a problem? Have you seen increased time frames at low temp. Please let me know if we need to take this off-line.

    Thanks for your help with this!

    Richard Elmquist

     

     

  • 0 in reply to Richard Elmquist
    TI__Mastermind 23116 points
    Hello Richard,
    Are you saying that there are more than one board doing this? It is highly unlikely that our parts would have that degree of variation due to temp. I would like to see signal waveforms with the communication and supplies of the part as this even occurs. Lets make sure the supply is as expected. The more detail they give us about the problem then more we can help. Lets find out if it is very repeatable.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Mastermind 45250 points

    Francis,

    Here is the customer's response:

    We are seeing this issue on 6 of the 24 boards that we are putting through thermal testing, so it is occurring on roughly 25% of our boards. It is also repeatable on the 6 boards as well, and they consistently have this problem when we first power them on after a 30-60 minute unpowered dwell at -40 degrees C. This is the only temperature where they experience this problem.

    I will request the information from the customer, but we probably will have to go off-line. I will let you know.

    Thanks for your help with this!

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    TI__Mastermind 23116 points
    Hello Richard,
    Did they swap known good parts on failed boards and parts from bad boards onto goo boards? Just would help show if it follows the part or the board.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Mastermind 45250 points

    Francis,

    I am going to take this off-line and email you directly.

    Thanks for your help with this!

    Richard Elmquist