This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS22914: Maximum allowable current for one pulse only

Part Number: TPS22914

Hi, Teams.

I would like to know the allowable inrush current that occurs only once at switch-on.

Let "A" be the area of the rectangle created by a current of 2.5 A and a pulse width of 300 µs, as described in Ipls (Maximum pulsed switch current) in the data sheet.

Let "B" be the area of the rectangle created by the peak value of the inrush current that occurs only once at switch-on and the pulse width.

Is it acceptable if area A > area B?
There is only one pulse of inrush current.

  • Hi Hayato-san, 

    Welcome to E2E!

    The Ipls specification to which you are referring is for a continuous pulse. 

    A one time pulse of inrush current would be specified differently. Do you know what inrush current you are expecting? If it is below 2.5A, you'll be ok. 

    Best Regards, 

    Elizabeth 

  • Thank you for your response.


    The inrush current I am assuming is 4.5A.
    The duration is 40us.

    The peak value is over 2.5A, but the duration is much smaller than 300us, so I would like to know the allowable inrush current for one pulse or how to calculate it.

  • Hi Hayato-san, 

    Thank you for the clarification.

    Although we do not specify that amount, allow me to check with our systems team to see if we can provide a ampere times time value and get back to you on Monday Aug. 1st

    Best Regards, 

    Elizabeth 

  • Hi Elizabeth-san

    Thank you for the suggestion.

    Please let me know the results of your checking with your systems team.

    Best Regards, Hayato

  • Hi Hayato-san, 

    Could you also let me know the DC current after the inrush?

    It looks like thermal simulations will be needed in which case I would need a power profile from you. 

    Also, are you using the TPS22914B or TPS22914C?

    Best Regards, 

    Elizabeth 

  • Hi Elizabeth-san,

    DC current after the inrush : 713mA

    Voltage : +1.8V (typ.)

    using : TPS22914C

    Please be specific about what you are looking for with the words "power profile."

    Inrush current waveforms are attached.

    Best Regards,

    Hayato

  • Hello Hayato-san,

    Is there any reason you're specifically using TPS22914C here? I think the best option would be to switch to a device with either a higher current rating, or with an adjustable slew rate (or fixed slow enough to lower inrush current). This is of course assuming the inrush current occurs during turn on of the device. If the inrush current occurs after passing a UVLO setting of a downstream device or based on some other event then slew rate control would be nearly meaningless and you would need to use a higher current rated device. 

    There are many potential options such as TPS22917 (adj slew rate control), TPS22971 (higher current rating), TPS22918 (adj slew rate control). I've also linked the product folder below.

    Load Switch Product Folder

    If you have any additional questions please feel free to reopen the post.

    Regards,

    Kalin Burnside

  • Hello, Kalin-san,

    Thank you for your suggestion.

    It would be nice if I could change to a device with a higher current rating, but it is very difficult to change devices due to the PCB development schedule.

    This inrush current is not generated by the turning on of TPS22914, but by another event in the downstream circuit.
    I am considering to generate the event in the downstream circuit slowly, but I still do not know if we can keep the current below the rated current of the device.

    I am asking this question because if you can tell me how to calculate the allowable values based on voltage, current, time, etc., I can find a guideline for not having to change the circuit or for moderating the downstream circuit event.

    Regards,

    Hayato

  • Hello Hayato-san,

    Due to the way the max pulse is characterized we're unable to provide a calculation that would offer the same guarantee that is offered from the specification in the D/S. 

    Is there any way you're able to have the cause of the inrush enabled before the load switch is turned on? If the inrush current occurs after the device is enabled it can't limit the inrush (not sure the details of your system in this regard). Due to the slew rate control It could limit the inrush current enough to make it a non-issue.

    Regards,

    Kalin Burnside

  • Hello Kalin-san,

    Thanks for your thoughts in the absence of details on our system.


    I am very disappointed that we were not provided with the calculation method.
    If you had told me in your first reply that you could not provide it, I would not have had to inquire for a week.

    Regards,

    Hayato