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TPS796: TPS79601 Powered off and 3.3V supplied onto pin externally OK?

Kevin Allen18
Mastermind 38295 points
Part Number: TPS796
Other Parts Discussed in Thread: TPS737, TPS7A37

Hi Team,

In my design I'm using TPS79601 for 5V to 3.3V conversion. There will be cases where TPS79601 is powered off (5V removed, EN off) and the 3.3V will be powered from elsewhere. Are there any reliability, or other, concerns with having 3.3V on the out pins and the device off for extended periods of time?

Reference schematic below:

Thanks,

Kevin

  • +1
    TI__Mastermind 29320 points

    Hi Kevin,

    For most LDO's, when Vout > Vin you can experience reverse current flow through the internal body diode of the pass FET.  This is not a desired mode of operation and usually we recommend no greater than 5% of the rated current ever flow through the body diode.  In your case, voltage on the output will result in current flow through the body diode trying to charge up Cin.  You will either need an LDO with reverse protection or some method to protect the LDO, such as a series diode on Vout.  A parallel diode across Vin and Vout of the LDO will not work as Vin is held fixed to 0V, so that will result in a heavy load on Vout.

    If you need a device with reverse current protection, there are plenty to choose from.  See the following link.  If you need guidance on a device, let me know your key requirements and I can help you choose one.

    www.ti.com/.../products.html

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Mastermind 38295 points

    Hi Stephen,

    Thanks for the reply, very helpful. I will review TI reverse current LDO options and then decide whether to go that route or add a series diode if sticking with TPS79601.

    I'm interested in a catalog LDO for 5V input, 3.3V output, and ~800mA to 1A current capacity (somewhat comparable to TPS79601). I found the options below for this, but appreciate if you know of others you can point me to:

    • TPS737 (3% accuracy)
    • TPS7A37 (1% accuracy)

    Best,

    Kevin

  • +1 in reply to Kevin Allen18
    TI__Mastermind 29320 points

    Hi Kevin,

    Those results are what I would recommend given your requirements.  I would go with the TPS7A37 as it is newer with better performance, if you can.

    Thanks,

    - Stephen