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TPS7B86-Q1: Inrush Current

Part Number: TPS7B86-Q1

Hi

My quiestion is What is the max inrush current?

In datasheet when Vin = Vout + 1V, Cout  = 2.2uF the values of output current limit is as below:

Is there any way to calculate when Cout is greater?

  • Hi Francisco,

    The specified current limit and the peak inrush current during startup are different and unrelated quantities. The reason for this is that inrush current is unregulated until the current limit circuit can respond and bring the current back down to the current limit. So, the peak inrush current is variable and increases for larger COUT, while the current limit is a fixed quantity for a given device (although it does usually vary with temperature). 

    With that said, did you mean to ask how to calculate the inrush current with a larger COUT and not the current limit?

    Regards,

    Nick

  • Hi Nick

    Sorry, how can I calculate the inrush current with a larger Cout?

  • Hi Francisco,

    Normally to estimate the peak inrush current, I would need a startup plot for the device when it does not start up in current limit. Unfortunately, the only startup plots we have are with COUT = 10uF, which results in starting up in current limit. I will be in the lab tomorrow, so I can capture a startup plot with a smaller output capacitor so that we can use it as a baseline to make a calculation. I'll update this post when I have more info.

    Regards,

    Nick

  • Hi Francisco,

    I don't have any of these devices in the lab so I'll have to order some. They will be here in 3-5 business days later next week. 

    While I'm at it, what COUT values are you interested in? I can capture the startup plot with a small output capacitor like I mentioned, and I can use a larger one that you are interested in to verify the calculation. 

    Regards,

    Nick

  • Hi Nick

    No problem, we are using two capacitors in parallel in Cout:

    One of them is ceramic (10uF, 10V, 10%, X7R) and the other is electrolytic (47uF, 16V, 20%)

  • Hi Francisco,

    I will see what I can do. Sometimes we have electrolytics like this in stock here in the office but not always. I'm also trying to locate some devices; they're out of stock from the normal place I get them so it might take longer than expected if nobody else in the office has any.

    Regards,

    Nick