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TPS22953: Add hysteresis to the load switch

d_zero
Genius 4775 points
Part Number: TPS22953
Other Parts Discussed in Thread: TPS22912C, TPS22990, BQ25892

Dear *,

we would like to add a hysteresis to the SNS or EN pin of the load switch.

we want to achieve following functionality, when the out voltage is falling and reaches 3.4V then the load switch must turn OFF, and then when the out voltage is rising we want to turn it ON when it reaches 3.6V

Is is possible to add this functionality to the TPS22953 load switch?

Best Regards,

David.

  • 0
    TI__Genius 10855 points

    Hi David,

    The TPS22953 has a precision enable pin, so it might be difficult to implement this functionality on this load switch. However, you could try implementing this functionality on a load switch with a larger VIH / VIL threshold, like the TPS22912C. You could connect a resistor divider on the EN pin such that EN is below VIL when VIN drops below VIL. The VIH threshold of the device has a larger difference, so it should turn on ~3.6V, but maybe not at that exact value.

    Thanks,

    Arthur Huang

    To find the latest information on Power Switches, visit www.ti.com/powerswitch

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Alpha H
    Genius 4775 points
    Dear Arthur,

    as our system can provide up to 5A , we need a load switch that is rated at 5A or more.

    Do you have any idea how to implement it on TPS22953 ?

    Best Regards,
    David.
  • 0 in reply to d_zero
    TI__Genius 10855 points
    Hi David,

    Would the TPS22990 work instead? The VIH / VIL threshold is larger than the TPS22953.

    I'm not sure if there's a way to implement it on the TPS22953. May I ask why the switch needs to turn on/off at this precise value?

    Thanks,
    Arthur
  • 0 in reply to Alpha H
    Genius 4775 points
    Hi Arthur,

    we are going to use BQ25892 battery charger ( e2e.ti.com/.../2953900

    and we want to achieve following, when the device is working only on battery, if the Vsys is below 3.4V or 3.35V to shut down the load ( UVLO feature), because the BQ25892 will go down to 2.8V or lover battery voltage, this is the first value.

    The second value is the turn on voltage to be something like 3.5V to 3.65V in order to to avoid that the system will turn on, off, on , off after the load is shut down and the battery voltage is recovered.

    I don't see that the TPS22990 has a UVLO?

    Best Regards,
    David.
  • 0 in reply to d_zero
    TI__Genius 10855 points
    Hi David,

    Thanks for the clarification. With this system configuration, the TPS22953 would be the best option.

    You could include a separate resistor divider on SNS, connected to VIN that only asserts high when the input voltage reaches 3.5/3.6V. Would this work instead?

    Thanks,
    Arthur
  • 0 in reply to Alpha H
    Genius 4775 points
    Hi Arthur,

    i'm sorry for the delay, i didn't see the replay.

    do you mean that we have two resistor dividers on SNS pin? one form Vin and on from Vout?

    please can you explain how will this work, or do you have a simple schematic ?

    Best Regards,
    David.
  • 0 in reply to d_zero
    TI__Genius 10855 points

    Hi David, 

    Correct, you can simple configure the device similar to the schematic on page 1 of the datasheet, but include the Rsns resistors on VIN instead of VOUT.

    Thanks,

    Arthur

  • 0 in reply to Alpha H
    Genius 4775 points
    Hi Arthur,

    i don't understand how will this make a difference ?

    Let say that the device is running on battery, and the battery is full, the battery voltage is 4.2V, the battery is discharging, and we want that the TPS22593 disconnects the load when battery voltage is approx. 3.4V. ( we can do this with UVLO, adjust the resistors on enable pin). After the load has been disconnected, because of no current flow from battery the battery voltage regenerates end goes to e.g 3.6V then the enable pin will go high, and when the current starts then it will go low again, ant this will repeat and this is not good for the battery.

    In theory we want that the load switch disconnects e.g. at 3.4V (when falling) and reconnects at 3.7V(when rising) ( hysteresis).

    If we connect the SNS pin to sens the input of the load switch, and set it to 3.6, 3.7V then the load switch will not work with Vin 3.4V 3.5V, if will disconnect if the voltage falls bellow 3.7V, or am i wrong?

    Best Regards,
    David.
  • 0 in reply to d_zero
    Genius 4775 points
    Hi Arthur,

    i did some calculation but this TPS22953 is not precise enough.

    The Ven rising from min to max is 100mV is to much also The Ven falling from min to max is 80mV.

    DO you have a comparator to recommend that has a better specification?

    Best Regards,
    David.
  • 0 in reply to d_zero
    TI__Genius 10855 points
    Hi David,

    Thanks for the clarification regarding the ON/OFF thresholds. Unfortunately, the TPS22953 precision comparator threshold is the closest we have for VIL/VIH control. Would the TPS22912C work instead? The threshold between VIH (1.1V) and VIL (0.6V) would be large enough of a difference to disconnect at ~3.3/3.4V and re-enable at a higher voltage.

    What are your thoughts?

    Thanks,
    Arthur
  • 0 in reply to Alpha H
    Genius 4775 points
    Hi Arthur,

    the TPS22912C is only 2A, we need 4.5A and up. I think we will need an external comparator with hysteresis + load switch.

    Best Regards,
    David.
  • 0 in reply to d_zero
    Genius 4775 points
    Hi Arthur,

    we decided not to go with load switch and comparator. We are going to use buck-boost for the critical rails and shut off the bat-fet on the battery charger via I2C with our host uP when the battery voltage is to low.

    Thank you for all the help,

    Br,
    David.