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DCP010512DB: Start up current for different capacitor values

David Daminelli
Prodigy 80 points
Part Number: DCP010512DB

Hello, 

Im using the DCP010512DBP-U on a board to power up some amp ops. As Im revision this project, I've measured the input current for different capacitors values. I will share my results:

To measure the current, I've used a 1.33Ohm resistor.

In all images, the yellow is the current signal, and blue is the input voltage.

1 - This is the first capacitors values:

 

Sometimes, after some turn on and offs, this is the signal I got:

2 - So, as the values aboves are not the same the datasheet recomends, I try the following:

 

3 - Finally, we have this, a little closer to the datasheet:

The 3rd test result in something that I didnt expect, as the capacitances are kinda the same as the datasheet.

Is this results that I've got consistent with the expected operation of this device? Why do I got this long transient on the 3rd circuit?

  • 0
    TI__Mastermind 30430 points

    Hello, to confirm you are measuring input current inrush as there are some concerns to hitting input supply current limit?

    Please be aware, this device does not have soft-start, so the device will try to regulate as fast as possible, so you can expect higher peak input current with larger output cap.

    It would be best to see the last waveform with output voltage recorded as well, in addition to input voltage and input current. 

  • 0 in reply to Marshall_Beck
    Prodigy 80 points

    I'm not concerned with supply current limit, this quick transients are not a problem. I made this measures to check the differences between capacitors values and choose the best one, as a transient like last one is not what I was expecting.

    I'll try to get this measure. Should I expect a lower peak input with lower capacitors? Is this long transient expected too?

  • 0 in reply to David Daminelli
    TI__Mastermind 30430 points

    Hello David,

    Figure 7-3 in datasheet can highlight typical startup performance.

    Where are you measuring the input current? Between input cap and DC/DC? I would expect to see a switched input current waveform. This appears DC.

    Lower caps values would result in reduced peak inrush current.