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TPS22934: Understanding this Part

Sherman Wilder
Prodigy 220 points
Part Number: TPS22934
Other Parts Discussed in Thread: TPS22810

Hi, I have been looking for a load side switch and came across the TPS22934 and it seems to be what I am looking for. 

I have a Capacitor that is rated at 3V and I want to discharge it to the load when it's almost full around 2.6V. Is that possible with this load switch? 

I am not understanding the datasheet too much. It says it has a hystererisis input of 2.35. So does this mean when the enable pin gets 2.35 V the switch will close and let the voltage flow through to the load?

Is there an under voltage where it detects low voltage around 0.9V to open the switch to disconnect from the load?

  • 0
    TI__Mastermind 32650 points

    Hi Sherman,

    I believe TPS22934 will work for your application.

    The hysteresis for this device refers to different thresholds for turn on and turn off of this device on the ON pin. The turnon range is between 2.1V to 2.7V while the turnoff range is between 1.3V to 1.7V which results in a hysteresis of 0.7V to 1.1V. Please refer to the electrical characteristics table in Section 6.5 of the datasheet for more information.

    UVLO is independent of the turnon and turnoff thresholds on the ON pin. When the voltage on the VIN pin (your capacitor) falls below 1.3V to 0.7V, the UVLO protection will kick in and turn OFF the device irrespective of the voltage on the ON pin. 

    Let me know if you have further questions. Thank you for choosing TI Power Switches in your designs.

  • 0 in reply to Shreyas Dmello
    Prodigy 220 points

    Okay thank you!

    For clarification, the switch will close when the input voltage is in between 2.1 - 2.7 correct?

    Then the switch will open when the input voltage is is between 1.3 - 1.7? Is there a way to have the switch to open at a lower coltage around 0.9V or 1V?

    Later when the voltage is below 1.3 - 0.7 or falls in between that range the switch will turn off completely?

  • 0 in reply to Sherman Wilder
    TI__Mastermind 32650 points

    Hi Sherman,

    There is a difference between input voltage and ON pin voltage that I believe is causing your confusion. The ON pin and the VIN pin have different thresholds.

    UVLO is the only threshold that the VIN pin looks into. Any voltage under the UVLO spec if present on the VIN pin turns off the device. This is irrespective of what voltage is present on the ON pin.

    The ON pin thresholds are control thresholds. You can think of the ON pin as a control pin. The thresholds on this pin refer to what voltage level the control signals have to be to turn on and turn off this device. The hysteresis refers to the fact that the voltage required to turn on is significantly different from the voltage required to turn off as some power sequencing applications require this.

    For example: 

    VIN = 3V

    VON = 3V

    RESULT -> DEVICE IS ON 

    VIN=3V

    VON=0.5V

    RESULT-> DEVICE IS OFF DUE TO CONTROL VOLTAGE 

    VIN=0.5V

    VON=3V

    RESULT->DEVICE OFF DUE TO UVLO

    VIN=0.5V

    VON=0.5V

    RESULT->DEVICE IS OFF 

  • 0 in reply to Shreyas Dmello
    Prodigy 220 points

    Wow! I think that makes sense. The ON voltage and the UVLO basically determines if the switch is closed or device is on.

    From what you said in your first response, the ON voltage min is 1.3V correct ?

    The UVLO threshold is min voltage is 0.7V?

  • 0 in reply to Sherman Wilder
    TI__Mastermind 32650 points

    Hi Sherman,

    Yes, The UVLO for this device will turn off the device anywhere between 0.7V to 1.3V. This is due to normal device variation.

    Basically, any voltage under 0.7V will trigger UVLO and any voltage over 1.3V will not trigger UVLO. Voltages between 1.3V and 0.7V is device dependent on whether UVLO is triggered or not.

    Similarly, there is device variation in the turnoff thresholds for the on pin. Any voltage lower than 1.3V on the ON pin will turn off the device but if the voltage on the ON pin is between 1.3V to 1.7V, the behavior is device dependent.

    I hope that I have answered your questions. Let me know if you have further questions on our Load Switch offerings.

  • 0 in reply to Shreyas Dmello
    Prodigy 220 points

    What is device dependent?

    And do you have any suggestions on how to decrease that ON voltage threshold to have voltage lower than 0.9V to turn off the device? Or do you have any other devices that could have the device turn off at 0.9V? And stay on above that?

  • 0 in reply to Sherman Wilder
    TI__Mastermind 32650 points

    Hi Sherman,

    By device dependent I mean the natural variation that may exist between one device to the next. This is why the specs are ranges and not fixed values.

    You cannot change the built in UVLO threshold. At this time, I do not think we have a device with UVLO that triggers only at 0.9V or lower. 

  • 0 in reply to Shreyas Dmello
    Prodigy 220 points

    The UVLO Voltages I'm not worried about too much, it's the ON voltage pin. I want the enable pin to have a 0.9V Trigger to turn off.

  • 0 in reply to Sherman Wilder
    TI__Mastermind 32650 points

    Hi Sherman,

    Please take a look at our portfolio here: https://www.ti.com/power-management/power-switches/load-switches/products.html

    All devices will have some range or undefined state between Vih and Vil.

    Will TPS22810 be okay for your application?

  • 0 in reply to Shreyas Dmello
    Prodigy 220 points

    For the voltages of the EN (ON) pin, are the highlighted values the numbers I'm supposed to be looking at correct? 

  • 0 in reply to Sherman Wilder
    TI__Mastermind 32650 points

    Hi Sherman,

    Yes those are the references for the EN pin.