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TPD4E0001 Low Resistance to Gnd

Steve Kozich
Prodigy 40 points
Other Parts Discussed in Thread: TPD4E001

Using TPD4E001DRL in a circuit where it is covered by an epoxy material (Loctite 3364). This is a Urethane Adhesive/Potting Compound. In this design the power pin is not connected and 2 of the signal pins are connected to analog outputs (0-5V). The ground pin is connected to ground and the other 2 signal pins are not connected. The issue we are having is that in a few cases a low resistance (80 ohms - 1K ohm) is developing between one of the connected signal pins and ground pin. At this point we have not been able to remove the potting compound to get at this part to examine it more closely. Is there a failure mode for this part where such a low resistance to Gnd pin could be created internally? Have there been any problems reported using this part with a potting compound?

  • 0
    TI__Genius 12190 points

    Hi Steve,

    This is not typical of any type of a failure mode with the TPD4E001, it should fail short or open. Were they tested before and after applying the epoxy?

    Regards,

  • 0 in reply to Guy Yater
    Prodigy 40 points
    Guy:
    Thanks for your reply

    They were not tested before applying the epoxy but they were tested right after applying the epoxy and no problems were seen at that point. The units that have developed this issue have been through some extreme temperatures (85C to -40C) and we suspect some issue with the potting material reacting with something on the PCB. At this point we have been able to remove all the other components connected to that circuit node since they were on the other side of the board which does not have the potting. The TPD4E001 is on the side covered in the potting and it is the only component left on the board that connects to that node. We just wanted to cover all bases and find out if there was any way the TPD4E001 could fail to that intermediate resistance value. We are hoping to be able to remove the potting material soon which may allow us to remove the TPD4E001 and determine whether it is playing any role in causing this issue.

    Steve Kozich
  • 0 in reply to Steve Kozich
    TI__Genius 12190 points
    Thanks for the information Steve. I don't believe that the TPD4E001 will fail in such a way. Can you remove it and let me know if the resistance is still there?

    Thanks,

    Guy
  • 0 in reply to Guy Yater
    Prodigy 40 points
    WIll do.

    I also have a question regarding the Breakdown Voltage Vbr spec for the TPD4E001. The data sheet gives this as 11V min. Does this apply to the zener diode from power to ground pins or the diodes connected to the IO pins?
  • 0 in reply to Steve Kozich
    TI__Genius 12190 points
    Hi Steve,

    Sorry that this is not clear in the data sheet. the Vbr of 11-V min applies to the IO pins. The Vbr of the VCC pin should therefore be that less a diode drop of 0.7 V.
  • 0 in reply to Guy Yater
    Prodigy 40 points

    I am still a little confused on something. The schematic in the data sheet shows 9 diodes in the array: 2 for each IO pin and one from power pin to ground. Are all 9 diodes the same? The reason I am asking this is because the symbol for the diode from power to ground is a zener symbol and the other diodes are shown as normal switching diodes so I assumed they were different. Can you clarify this?

    Thanks.

    Steve kozich