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TPS22920: inrush current control with high capacitive load possible ( 2000uF )

Bertram Brummer
Intellectual 1686 points
Part Number: TPS22920

Hi,  

I have an application with a high capacitive load of 2000uF sitting on a plugable board.  Main reason for the 2000uF is that the board can be unblugged and the power need's to stay up and running so that the supply can run a controlled power down sequence.

The issues is that when the board is plugged in, the TPS22920 will, when the baord is detected, switch on and charge the cap, but based on the  guidllines from the Datasheet the inrush current should not exceed  40mA is this a correct reading?   Since the switch can handle 4A RMS and 6A peak, I wonder why there is a limit of 40mA?

What is from Design point o view the max. ammount of capacitance which could be used with the TPS22920  when using a 3.3V supply?   

If using a supply (Vin) which is always on and can support a fast transient response , would you still request Cin 10x Cout  ?

If you think the TPS22920 is the wrong device for this kind of application, what would be your advice ,  should we use mor a eFuse or a hto swap device since you can limit the current easier ? Any advice suggestion is OK 

Looking forward to your feedback.

  • 0
    TI__Genius 13650 points

    Hi Bertram,

    Thank you for reaching out to the E2E forum!

    You are in fact misinterpreting the 40mA reading. That is just a desired maximum inrush current from an example system to calculate the necessary slew rate to keep the inrush current under the 40mA.

    The TPS22920 does in fact have a maximum continuous output current of 4A and can withstand a pulse current of up to 6A. as long the inrush current does not exceed these values the device should be fine. Unfortunately with an output capacitance of 2000uF you would be exceeding the 6A rating of the TPS22920. The inrush current can be calculated with  I = C * (dv/dt). The typical slew rate for the TPS22920 @3.3V is about 3.75 V/ms. Using the equation with your capacitance value you would be getting about 7.5A of inrush current. The TPS22920 may be able to withstand this current, but the integrity of the lifetime of the switch would depend on the frequency of these current spikes which would happen whenever the load switch is enabled. For this reason I would recommend looking for other devices. I will look for suggestions from a load switch stand point, but it might be worth it to start looking into efuses and hotswap devices.

    Is there a reason why you went for a load switch specifically?

    If you have any questions regarding efuses and hot swaps create another thread and tag a device like you did with the TPS22920 so the correct team member can help you address this issue. I'll work on my part to see if a load switch can fit your design.

    Best regards,

    Andy Robles

  • 0 in reply to Andy Robles
    TI__Genius 13650 points

    Hi Bertram,

    Haven't heard from you in a while. I hope you were able to fix your design problem. If I can help you with anything else feel free to open a new thread or keep commenting on this thread.

    Best regards,

    Andy Robles