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TMP107: TMP107 Hot Plug

Dave Lacerte
Prodigy 20 points
Part Number: TMP107

Hi!

Is there any problem with hot plugging the TMP107. I see in the datasheet that IO1/IO2 can only be at V+ + 0.3V.

The communication bus is driven (in my design) by a 1k pull-up and a 5V power line (the same used to power the TMP107). I have no guarantee that the power will be applied first when connected to the system. I have a 10 ohm in line on the SMAART wire line.

So the maximum current during the hot plug would be ~4.7mA. Nothing in the datasheet specified the maximum current for this scenario. 

If it is dangerous for the TMP107, have you something in mind to protect against it ?

Thanks,
Dave Lacerte


 

  • 0
    TI__Mastermind 44140 points

    Hello Dave,

    To be sure I understand correctly, you have the pull up resistors and supply pin tied to the same voltage, right?  This means that the IOs should be pulled up at the same time as the supply when it is plugged in.  This would not violate the specification.  Let me know if you can clarify further or if there is something I am missing.

  • 0 in reply to Eddie LaCost
    Prodigy 20 points

    Thanks Eddie for your fast answer.

    Pull-up resistor for SMAART communication and supply pin are at the same voltage level. 

    But we don't use a special connector with longer pins on supply so we can't guarantee that the power will be connected at the same time as the communication line if the connector is inserted with an angle.

  • 0 in reply to Dave Lacerte
    TI__Mastermind 44140 points

    Thank you for the additional information.  I understand your concern now.  

    I'm looking into this and will provide an update when I have more information.

  • 0 in reply to Eddie LaCost
    TI__Mastermind 44140 points

    Dave,

    As you described, it is possible with this configuration that the communication line could be connected first if the connector is angled.  We can't guarantee anything that is outside of the datasheet specification.  There is an internal ESD protection diode between the pin and the supply, which would back supply V+ with one diode drop voltage.  

  • 0 in reply to Eddie LaCost
    Prodigy 20 points

    Hi Eddie,

    Thanks for your answer.

    Will it damage the TMP107 if there is a 4.7mA in the ESD protection device (5V-0.3V)/1000ohm during a small amount of time ? Do you have any suggestion if so ?

    Thanks

  • +1 in reply to Dave Lacerte
    TI__Mastermind 44140 points

    When the IO exceeds V+ by 0.3V, V+ will rise.  The device can survive operation this way, but it is not specified how much current can pass through the ESD protection structure.  Though we have no specific reason that it wouldn't survive, it is a violation of the datasheet spec and we cannot guarantee anything outside of spec.