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output 0 Volt - mosfet short circuit

Part Number: TLV61048

Tool/software:

Dear TI-Team,

The booster was isolated from my PCB. I powered it directly with a 5 V power supply limited to 1 A. The output is floating. The output MOSFET fails immediately, and I measure a short between SW and GND. I can't understand what happens and what i do wrong. You have some explanations ready?^^

Attached are an oscilloscope screenshot and .csv file showing startup behavior on a booster that initially still works, as well as the PCB layout and schematic. In parallel with the 10 µF output cap, I also added 10 µF and 1 µF MLCCs.

yellow: input should be 5V, only reaches 3.04V. then at the noise, up to 3.68V

purple: feedback 0.8V, only 0.34V. At noise -> up to 1V

Turquoise(blue): stays low

green: current at input. goes into current limit of power supply 1A, while booster is switching. then low again.

scheamtic:

 TLV61048_smashed_osci.CSV

Thanks for your help in Advance.

best regards

Patrick

  • Hi Patrick,

    The schematic and layout is correct. You need to check why your input supply cannot reach 5V. And please ensure the device and diode direction is correct. From your waveform, the device should not be damaged.

    Could you measure SW waveform next time?

    Thanks.

  • Hi Shipeng,

    Sorry, forgot to mention — the turquoise line is the SW output. It stays low the entire time. I couldn’t believe it at first either, so I double-checked the oscilloscope probe — it’s working fine. I also considered a short at the output, but couldn’t find one apart from the damaged MOSFET.

    The input supply should easily provide 5 V, also measured with osci, seems fine. Could input noise be destroying the MOSFET immediately? If you look closely, there's a spike when I power on the supply.

    I’ve checked all components: the diode is correct, the IC looked fine — I could initially measure the MOSFET’s body diode. But after powering it up, the body diode from GND to SW is gone — it’s now a direct short. Resistor values are also correct.

    Any further suggestions?

    Thanks.

  • Hi Patrick,

    There's also ESD diode on each pin to GND, maybe you think it is MOSFET. So are you sure the device direction is correct? The circuit is simple so I don't think it's a complex issue.

  • Hi Shipeng,
    I don't think that's the issue, but just to be sure, I soldered another one in the opposite orientation. Unfortunately, that didn’t help — so it seems the original one was already the correct way around.



    I'm out of office for a week. But feel free to make other suggestions, if something jumps to your mind. 

    Thanks. 

    Patrick

  • Hi Patrick,

    I can only say your schematic and layout is correct. So I think there's a mistake somewhere. Give you some guidance, you can check it.

    1. Solder another board and try again. Add more capacitors at input side.

    2. Check the device marking is "1VSF", to see if you pick wrong device.