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TPS22914: Reverse current and power supply floating ground

Yixin Ma
Prodigy 220 points
Part Number:

Hi TI experts,

I want to use load switch TPS22914 to direct continuous current from power supply to two loops.
The design circuit is as attached. I have a few concern regarding it:

1) Currents have to be bi-directional (some value between -2A to 2A). I want to make sure this part (without reverse current block/protection) can handle current in two directions.
2) The power supply is floating ground. How to limit Vin and Vout (referenced to the ground of the parts) to below the maximum rating?
I noticed that in the evaluation board, Vin is voltage limited and referenced to the ground. However, I'm current-limiting the current between Vin and Vout. I'm not sure how the part works for this 'current limiting' design.
3) Do you have any recommendations for choosing the value of C1, C2, and C3? In the case of current flowing in two directions, I would think they should be of similar value (~1 uF)?

Thank you in advance.

Yixin

  • 0
    Prodigy 220 points

    Yixin Ma said:

    Part Number: TPS22914

    Hi TI experts,

    I want to use load switch TPS22914 to direct continuous current from power supply to two loops.
    The design circuit is as attached. I have a few concern regarding it:

    1) Currents have to be bi-directional (some value between -2A to 2A). I want to make sure this part (without reverse current block/protection) can handle current in two directions.
    2) The power supply is floating ground. How to limit Vin and Vout (referenced to the ground of the parts) to below the maximum rating?
    I noticed that in the evaluation board, Vin is voltage limited and referenced to the ground. However, I'm current-limiting the current between Vin and Vout. I'm not sure how the part works for this 'current limiting' design.
    3) Do you have any recommendations for choosing the value of C1, C2, and C3? In the case of current flowing in two directions, I would think they should be of similar value (~1 uF)?

    Thank you in advance.

    Yixin

  • 0 in reply to Yixin Ma
    TI__Mastermind 32650 points

    Hi Yixin,

    Once the load switch is turned ON, current can flow in both directions. TPS22914 can handle two way current but one issue that I foresee with using TPS22914 as a bi-directional switch is the when turned OFF, there is still a reverse diode path through the body diode. To get around this I would recommend using the TPS22953 which only blocks reverse current when disabled.

    If the supply is connected in such a fashion, the device GND is not actual GND(-ve supply voltage) for this system. This could lead to overvoltage failures in the worst case or may not even turn on. Is it not possible to connect the negative of the supply to GND? These devices are not meant to be used with "floating supplies".

    There is no strict recommendation for input an output capacitance. Enough input capacitance is required to provide the inrush current and protect the supply from drooping in voltage. The output capacitance is dependent on your load condition.

  • 0 in reply to Shreyas Dmello
    Prodigy 220 points

    Hi Shreyas,

    Thank you a lot for your reply.

    I don't think we can put the negative output of the power supply to the ground.

    Shreyas Dmello said:
    These devices are not meant to be used with "floating supplies".

    Do we have any devices that are compatible with the floating supplies?

    All the best,

    Yixin

  • 0 in reply to Yixin Ma
    TI__Mastermind 32650 points

    Hi Yixin,

    As long as there is some voltage regulation on the supply, then there is no issue. To do so would involve some connection to GND. Perhaps a zener diode on the input and output rails could help? If there is no regulation, then the voltage may hit unsustainable levels for the device.

    If there is no regulation, then I doubt if a Load Switch would work here.

  • 0 in reply to Shreyas Dmello
    Prodigy 220 points

    Hi Shreyas,


    Thank you very much for your reply.


    While I'm looking at the voltage regulator or Zener Diode to protect Vin and Vout, I want to ask if there is any other kind of switch (other than the load switch) that might also be suitable for this design so that I should keep an eye on as well.


    All the best and happy new year!


    Yixin

  • 0 in reply to Yixin Ma
    TI__Mastermind 32650 points

    Hi Yixin,

    Unfortunately, we do not have any such device in our power switch portfolio.

    Apologies for the inconvenience and have a wonderful new year.