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TPS2121: Damage to the output observed

Aaron Dobbins
Prodigy 100 points
Part Number: TPS2121
I have a TPS2121 MUX managing 5V from one of two independent 5V power supplies that may or may not both be present and delivers 5V to a single output and had a scenario where I seemed to have destroyed the chip:
On the malfunctioning chip here is what I observe:
The output is measuring 70 ohms of impedance with the chip unpowered.  
When the IN1 is given 5V with IN2 at 0V, the output is periodically attempting to turn on with blips of 1.2 V every 40ms or so.  (capture below)
Application of 5V to IN2 with 0V on IN1 results in a steady 0V on the output.

My system runs off of 24V DC but both inputs should only ever see 5V nominally from low voltage supplies.  
Here is a snippet of my circuit
My 5V input on IN1 is well established and has lots of capacitance on the net.  The IN2: PWR net is brought in from another board (where it is not always present) and I do not have any capacitance locally on this board.  I am wondering if maybe this made me vulnerable to an ESD hit on this input upon cable connection.  Can you please advise if ESD on IN2 could damage the part in the manner in which I observed or if any other factors could be responsible?
Thanks for the support!
  • 0
    TI__Mastermind 32650 points

    Hi Aaron,

    From the information presented, it is not possible to confirm what is the issue here. These devices are rated to 24V and so the surge event has to be significant to damage it. 

    What is the test that you were running when the failure occurred? Can you replicate this issue on other TPS2121 devices? When you are turning on the device, what is the load current and nature of the load?

    Feel free to email me directly at s-dmello@ti.com for direct email support if you are not comfortable with posting this information.

  • 0 in reply to Shreyas Dmello
    Prodigy 100 points

    The load draws only a couple hundred milliamps from the PowerMUX 5V output.  At the time the damage occurred, the load was on steady state.  The IN1 state should also have been a solid 5V the entire time.  The damage happened when a cable harness was connected to the IN2 signal (but I believe was unpowered, unless there was a cable malfunction, but even then I only have 24VDC at most available in that harness).

  • 0 in reply to Aaron Dobbins
    TI__Mastermind 32650 points

    Hi Aaron,

    If for some reason the cable had 24V on there and was input into TPS2121, the inductive ringing that could occur may case a surge event that could damage the device. It is tough to say the extent of damage that could occur in an electrical overstress event but any voltage over the abs max could damage the device. 

    Some sort of TVS suppression would be helpful if this was the situation. Do you have any waveforms that describe this test? Was this a single failure or have you found other boards being damaged as well?

  • 0 in reply to Shreyas Dmello
    Prodigy 100 points

    So far it is a single board that failed while I wasn't expecting to be stress testing boards.  I tried ESD zapping a second board through a cable harness that leads into that IN2 connection and have been unsuccessful at causing the power mux to fail in a similar way.

    Is there anything about the described type of damage I observed at the chip that tells me anything about the path of energy that killed it?  (70 ohms across the output, the attempt of the power switch to cycle on from IN1 path to the output whereas no attempt at all to power on from IN2 path to output)?

    THanks for the support!

  • 0 in reply to Aaron Dobbins
    Prodigy 100 points

    I realized there is about 23.5V coming out on my cable that caused the problem leading to the IN2 input - I suppose it is what you suggest afterall ringing on the cable pushing the Vin beyond the abs max rather than ESD.

    I will put in provisions to knock down the voltage to avoid damage on my circuit.  Thanks!