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TPS22950: Reverse current protection of TPS22950C

Hirotsugu Kobayashi
Mastermind 8725 points
Part Number: TPS22950

Hi team,

I have two questions.

1. Does TPS22950C have a reverse current protection function?

  I biased the OUT side to 5V while outputting 3.3V, but the reverse current continues to flow. It does not turn off like the data sheet.

2. Two patterns occur when VIN is turned off with the OUT side biased to 5V.
　　Case A: Vin drops to 0V
　　Case B: Vin rises to 5V
　B occurs more frequently, but which is the expected behavior?

Best Regards,

  • 0
    TI__Mastermind 18510 points

    Hi Kobayashi-san,

    1. The reverse current blocking is active when either the device is disabled, or when VOUT - VIN > 44mV. Since VIN in the picture you sent is not pulled to 3.3V from a power source, there is nothing forcing a difference between VOUT and VIN, which is why VIN rises to VOUT. Based on the picture you sent, VOUT - VIN = .034Ohm*.5A = 17mV, or on a similar scale, which is why reverse current blocking does not activate.

    2. Case A is the intended behavior. Right before VIN drops to 0V, it looks like the rail is powered to 3.3V (I assume by an upstream converter). This creates the voltage drop of > 44mV, and thus the device quickly disables reverse current.

    This issue can be addressed by disabling the TPS22950 when VIN is not being powered (either through external signal or by tying ON to VIN) or by ensuring VIN is always powered to 3.3V whenever VOUT is pulled up to 5V.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Mastermind 8725 points

    Hi Patrick,

    I understand how it works.
    Unless the power supply can sink current from the OUT side, there will be no difference between VIN and VOUT.

    Even if ON and VIN are tied, if VIN is floating, it will be charged from the OUT side and cannot be turned off.

    Do you have any good ideas?

    Best Regards,

  • 0 in reply to Hirotsugu Kobayashi
    TI__Mastermind 18510 points

    Hi Kobayashi-san,

    What type of power source is connected to VIN? It looks like the behavior of it can differ, based on the Case A picture you sent where it sinks current, and Case B where it doesn't.

    Yes, that's true. Do you have an external signal you can use to drive the ON pin low when VOUT = 5V? If not, maybe you could use a comparator + resistor divider to monitor the output and turn off the device if VOUT is powered by anything other than VIN.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Mastermind 8725 points

    Hi Patrick,

    I changed the power supply source only type.

    When a voltage higher than the input is applied to the OUT side, VIN rises, but there is no difference between IN and OUT and reverse current continues to flow.
    In the case of a source-sink type power supply, the protection function of the power supply is activated and the power supply stops.
    In what cases does the always reverse current protection function work effectively?

    Best Regards,

  • +1 in reply to Hirotsugu Kobayashi
    TI__Mastermind 18510 points

    Hi Kobayashi-san,

    It looks like the source-sink power supply protection function is more sensitive than the TPS22950 reverse current protection. The reverse current protection works effectively when there is a source-sink power supply that has no sink protection (or sink protection that triggers above 900mA of reverse current), such as a battery.

    Thanks,

    Patrick