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TPS7A4701-EP: Part damaged by phantom power

David Wende
Intellectual 690 points
Part Number: TPS7A4701-EP


Tool/software:

Hello,

The actual part is TPS7A4700.

We suspect that this part is being damaged by phantom power delivered to the output via the load amplifier.

See the attached partial schematic.

The current source consisting of U128, U127 is supplied by +15V and -5V volts by U126 and U125 respectively.

The U126 seems to be damaged on two boards already, and we suspect this may be due to the -5V supply at the amplifiers being transferred through the amplifiers into the +15V output of the LDO.

The maximum rating of this output pin is -0.4V to 36V, and we are seeing (sometimes) close to -1V at the output.

So, two questions:

1. Does this explanation make sense?

2. Could you suggest a fix to the circuit to prevent this happening? We thought of either power sequencing (the + first, then the -), but this may not be possible. Another idea was to place a schottky diode at the LDO output to prevent large negative voltages here.

Thanks

David

.question_to_TI.pdf

  • 0
    TI__Guru 50025 points

    Hi David,

    That seems like a reasonable explanation, especially if you are measuring -1V at the output. My first thought was to put a Schottky diode at the output to clamp the voltage as well. The -0.3V rating is due to the ESD cell, which conducts at a forward voltage similar to a stand PN junction diode, i.e. around 0.6V where it's fully conducting. So, a Schottky diode should prevent the ESD cell from conducting and I would expect it to solve the issue.

    Regards,

    Nick