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LM25118: Buck boost converter is not sourcing in the RLC Circuit || sourcing the current in the pure R load

JAYAKRISHNAKUMAR S
Prodigy 160 points
Part Number: LM25118

In LM25118MH, an Input of 9V was given and an output of 28V has been generated.

We had done some experiments like connecting the other boards (Input voltage of 28V in 3 numbers)in parallel to the buck converter by tapping out

we had done power budgeting for the working board of 3 numbers(which is acting as an RLC load) it is not exceeding the maximum load current of the buck-boost converter.

But while connecting the first board, buck-boost can able to source the current.

Then we try tried to increase the load by hot plugging the second board. At this time we are observing that the Buck-Boost converter cannot able to source the current to the second board.

At the same time, we had tried with the pure resistive load, at the time current is sourced from the buck-boost converter

we are suspecting that it is due to the capacitive effect. due to the capacitive effect, Inrush current is more while doing the hot-plugging of the second board.

Is that a real reason behind that? or something else? what will happen internally in buck-boost converter

  • +1
    TI__Mastermind 47241 points

    Hi Jayakrishnak,

    thank you for using the E2E forum.

    You are right, this is related to the capacitive load which is connected. 

    Keep in mind compared to a resistive load a capacitive load the time of connection would behave like a short.

    So if you can better control the inrush current then this should solve the problem.

    Also check the ratio of the output cap of your first power stage to the input cap of the following once. Maybe you can reduce the input cap. Also ensure that your softstart time of the second power stages have a long enough time to reduce the inrush current to the lowest possible level.

    Best regards,

     Stefan