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TLV774: Reverse current limit

Yasuaki Sugimoto
Prodigy 50 points

Part Number: TLV774

Hello,

 

In a circuit design using the TLV77433, due to system limitations, a voltage of 0.9V sneaks into VOUT from an external source during the approximately 900ms period when VIN is 0V after power-on. The reverse current value at this time is limited to less than 0.4mA. According to the datasheet, to avoid damaging the device, the reverse current should be limited to less than 5% of the rated current for a short period of time. I believe 0.4mA meets this condition, but does 900ms fall within the short-term range? I am considering an application where the power supply will be started up several times a day.

 

Kind regards,

Yas

  • 0
    TI__Expert 4910 points

    Hi Yasuaki,

    The device should be fine in this scenario. The main concern is if the pass FET body diode can handle the reverse current power dissipation. In this case, since the reverse current magnitude is so small, the body diode should be fine, even for the extended 900ms duration.

    Best,

    Aden

  • 0 in reply to Aden Taylor
    Prodigy 50 points

    Hi Aden,

    Thanks for your answer. I have limited board space and it would be difficult to find space for additional bypass diodes, so I'm relieved that it doesn't seem necessary.

    Just to be sure, the datasheet doesn't state the allowable reverse current for this LDO, but if it's up to 5% of the rated 300mA, does that mean that if I limit it to less than 15mA, the device won't fail?

    Kind regards,

    Yas

  • 0 in reply to Yasuaki Sugimoto
    TI__Expert 4910 points

    Hi Yasuaki,

    As is now, the 0.4mA reverse current is likely fine for 900ms. However, I would caution against raising that closer to the 15mA for the same 900ms duration. I can't guarantee that it won't fail if you increase the reverse current to 15mA as the extended 900ms duration will cause significant power dissipation over the body diode.

    Best,

    Aden

  • 0 in reply to Aden Taylor
    Prodigy 50 points

    Hi Aden,

    What I really wanted to know was not whether there would be any problem up to 15mA, but whether there was enough margin at 0.4mA. You told me in your previous answer that the body diode should be fine, but if there isn't much margin, I think I need to limit the current a little more.

    Kind regards,

    Yas

  • +1 in reply to Yasuaki Sugimoto
    TI__Expert 4910 points

    Hi Yasuaki

    Unfortunately this problem is not something that is well characterized for this device. As stated previously, the amount of reverse current stated is under the specified 5% in the datasheet and therefore from a thermal perspective should be ok. However, there are no guarantees for this as, again, this is not something that is well defined and characterized for this device. If the device fails from this then the only thing I can recommend is to put in place reverse current protection such as a Schottky diode in series with the input or a Schottky diode from output to input to prevent this problem altogether.

    Best,

    Aden