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LM5050-1: Reverse polarity protection, failures during production test

Martin Gaeumann
Prodigy 60 points
Part Number:

Hi all

We use the LM5050-1 as an ideal diode in the input circuit of a power supply, mainly to reduce power losses compared to a normal diode.

Schematic:

During production test, around 10% of the devices fail during reverse polarity test (power supply ramps up to -50.4V with 1R series resistance).

Failure modes:
1. No visible defect: change of LM5050 resolves the problem
2. LM5050 Pin Nr. 6 burnt: change of LM5050 resolves the problem
3. R117, D104 and D105 burnt, LM5050 and C116 discolored laquer

Compared to the recommended application for reverse input voltage protection, I see the following differences:
C116 not used
D105 Schottky instead of a normal diode
D104 Schottky with lower forward voltage / higher current rating

I've done many tests with one example and was not able to destroy it, does anyone see some weak spots which could lead in the described failures?

Thanks in advance
Martin

  • 0
    Prodigy 60 points

    Martin Gaeumann said:

    Part Number: LM5050-1

    Hi all

    We use the LM5050-1 as an ideal diode in the input circuit of a power supply, mainly to reduce power losses compared to a normal diode.

    Schematic:

    During production test, around 10% of the devices fail during reverse polarity test (power supply ramps up to -50.4V with 1R series resistance).

    Failure modes:
    1. No visible defect: change of LM5050 resolves the problem
    2. LM5050 Pin Nr. 6 burnt: change of LM5050 resolves the problem
    3. R117, D104 and D105 burnt, LM5050 and C116 discolored laquer

    Compared to the recommended application for reverse input voltage protection, I see the following differences:
    C116 not used
    D105 Schottky instead of a normal diode
    D104 Schottky with lower forward voltage / higher current rating

    I've done many tests with one example and was not able to destroy it, does anyone see some weak spots which could lead in the described failures?

    Thanks in advance
    Martin

  • 0 in reply to Martin Gaeumann
    TI__Genius 10370 points

    Hi Martin,

    Welcome to E2E!  Is this an automotive application?

    Thank you for providing the schematic. It seems you're right on the money about changes to be made on the schematic. I would recommend depopulating C116. The issue looks like the diodes chosen are not strong enough for this application. The IC might break if Schottky diodes are not chosen (abs max on IC pins are -0.3V), and the Schottky diodes chosen need to be strong enough to handle the power going through them.

    Also, I didn't see a TVS diode at the output of the LM5050-1. Please add one and make sure it connects to IC ground and not system ground (look below). I would recommend the Schottky diode and TVS diode part numbers that are on our EVM board: http://www.ti.com/lit/ug/snva458a/snva458a.pdf. 

    I hope this helps :-)

    Best Regards,

    Aramis P. Alvarez

  • 0 in reply to Aramis P. Alvarez
    Prodigy 60 points
    Hi Aramis,

    Thanks for your fast feedback!

    I have already suspected the diodes and C116, so this gives me some confirmation...
    We'll give this to our manufacturer and I'll reply if this solved the problem.

    Best regards
    Martin