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TPS22924C large inrush current

K. Sasaki14
Guru 10200 points
Other Parts Discussed in Thread: TPS22924C, TINA-TI, TPS22924D

Our customer observed large inrush current with TPS22924C at Vin pin tied to ON pin condition. 

We can observe this phenomenon on TINA-TI simulation. Load condition is 100uF capacitor only.

And this large inrush phenomenon does not occur when ON signal is added after Vin. So I think this device has power on delay after Vin is added. Do we must add ON signal after Vin to resolve inrush current? If my idea is correct, please let me know the delay time. 

And TPS22924D has longer slew rate than TPS22924C. However is there possibility that the same phenomenon occurs? Or doesn't this phenomenon occur if TPS22924D is used?

Our customer can't separate Vin and ON, thus they are considering to put RC filter on EN pin to make delay time. Is this method valid?

Best Regards,

Kohei Sasaki

  • 0
    TI__Genius 15740 points

    Hi Kohei,

    The amount of inrush current for any of our load switches is dependent on the controlled rise time for that device.  When both VIN and ON are tied together, the controlled slew rate for the device cannot be guaranteed because the device has not had sufficient time to power up.  To ensure the proper rise time for the device, the ON pin signal should be applied after VIN.  Unforutnately, the amount of time it takes to fully power on the device through VIN is not a parameter we usually test.

    The TPS22924D will have the same inrush current problem if VIN and ON are tied together.  Your customer's solution of putting an RC filter delay on the enable pin should be able to fix this issue.  If you are able to give us more details about the application (input voltage, input signal slew rate, schematic) we may be able to look into this further.

     

    Regards,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Guru 10200 points

    Alek-san,

    Thank you for your prompt reply. I understood the inrush problem. Does this problem occur even in the case of current limit switch?

     

    Their application detail is not fixed condition, input voltage is 3.3V, Vin and ON are tied together (it is possible to put RC filter), slew rate is vary depend on system, Cout is max 100uF and initial load condition is about 300mA.

    We are considering to use TINA-TI simulation for operation confirming and decide component value.

     

    Best Regards,

    Kohei Sasaki

  • 0 in reply to K. Sasaki14
    TI__Genius 15740 points

    Hi Kohei-san,

    Even a current limited switch would have this problem because the current limit circuitry is not active until the part is powered on.

    The delay between VIN and ON should be at least the turn on time for the device (tON).  We have a typical value in the datasheet of 800us, but this can vary due to process and temperature.

    I will check with our modeling team to make sure that our TINA-TI models accurately simulate this specific device behavior.

     

    Regards,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Guru 10200 points

    Alek-san,

     

    Thank you for your response. I will wait for your information about TINA-TI models accurately.

    You said the delay between Vin and ON should be at least tON time, TPS22924C is 800us, however TPS22924D is 6200us. I think this period is too long as a power on delay. According to simulation, 40us delay between Vin and ON is enough to become active slew rate control circuit. Thus I thought 100us delay is enough in view of the margin.

     

    Best Regards,

    Kohei Sasaki

  • 0 in reply to K. Sasaki14
    TI__Genius 15740 points

    Hi Kohei-san,

    I have just talked to our modeling team and have confirmed that our TINA-TI models do not represent this behavior accurately.  To guarantee a controlled rise time on our device we recommend having VIN high before the ON signal is toggled.  Our models only represent this behavior.  If both VIN and ON are pulled high at the same time then the controlled slew rate would still be seen in the simulations.

    Regards,

    Alek Kaknevicius

  • 0 in reply to Aleksandras_Kaknevicius
    Guru 10200 points

    Alek-san,

     

    Thank you for your support. I understood that we should add ON signal after Vin becomes high, however there is no guaranteed time characteristic, so we should confirm with actual device operation insted of simulation and decide the delay time with enough margin.

    I understand the inrush occurs when ON signal becomes high just after Vin becomes over 0.75V.

     

    Best Regards,

    Kohei Sasaki