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TPS7A8101: max allowed reverse current

Hans
Genius 12865 points
Part Number: TPS7A8101
Other Parts Discussed in Thread: TPS7A89, LP5907, TPS7A47, TPS22910A, TPS62913

Hello Team,

can you provide the max reverse current, please? If Vin drops down to zero volt rapidly the body diode may see too much current source by the output capacitor.

So this is important to know. 

Can you also provide the max reverse currents for TPS7A71, TPS7A47, TPS7A89 and LP5907, please?

Can we assume the reverse current to be as high as the specified output current for each part?

Thanks and Best Regards,

Hans

  • 0
    TI__Mastermind 45785 points

    Hi Hans,

    With devices without integrated reverse-current protection, we recommend limiting the reverse current to less than 5% of the rated output current. If the input in your application will collapse quickly, then a diode from OUT to IN may be necessary, or alternatively, a diode at the input before the input capacitor to prevent the device input from collapsing when the main supply collapses. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Genius 12865 points

    Hi Nick,

    here are the conditions: Vin=5.5V, Vout=5.2V, Iout=75mA. Cin = 10µF, Cout = 22µF

    The load is switched off (and on) very fast by TPS22910A within 10µs and transient spikes may occur which overshoot the max Vin. Can you confirm that for this application no reverse Schottky diode is required?

    Thanks and Best Regards, Hans

  • 0 in reply to Hans
    TI__Mastermind 45785 points

    Hi Hans,

    So the load is switched from 0mA to 75mA in 10us repeatedly? This seems like a different scenario than the original description of the input voltage falling to 0V quickly. Please confirm the application.

    Is it possible for them to increase CIN to 20uF? I think that would eliminate the concern of a load transient causing VIN to droop below VOUT.

    I'm currently working from home because of an injury, but I will see if I can get some help from someone in the office to test this. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    TI__Genius 12865 points

    Hi Nick,

    maybe my English needs to be improved...

    10us is the rise and falltime. But not periodically. Just occasionally. I hope this is clear now.

    Thanks and Best Regards, Hans

  • 0 in reply to Hans
    TI__Mastermind 45785 points

    Hi Hans,

    No worries. Just to be clear, the 10us rise and fall time is for the load transient, right? What was the comment in the original post about the input falling to 0V?

    Also what about the question of increasing the input capacitance?

    Thanks,

    Nick

  • 0 in reply to Nick Butts
    TI__Genius 12865 points

    Hi Nick,

    yes, the 10us is for the load transient.

    The TPS7A81 is sourced by TPS62913 which supports output discharge. I did some calculations and with Rdis=32Ohm the reverse current is far below the 95% specified output current. So, no further questions.

    Thanks and Best Regards, Hans

  • 0 in reply to Hans
    TI__Mastermind 45785 points

    Hi Hans,

    Did you mean to say 5% specified output current? Because 95% of the specified output current in the reverse direction will definitely destroy the device. 

    Thanks,

    Nick