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LP2980IM5-3.3 Regulator output capacitor assistance

Tim Anderson1
Prodigy 120 points

This forum was previously very helpful with questions regarding the LP2980IM5-3.3 regulator.

I apologize, but I have another question that I need help resolving. Concerning the same regulator and selecting the appropriate capacitor connected to the output, I would like to use a multi-layer ceramic 0603 4.7uf 16-volt cap for this application. Below is the ESR plot for this capacitor. The difficulty i'm having is knowing the

frequency to use for this regulator to see if the ESR is acceptable. I've attached a PDF of TI file SNOA842 regarding the selection process, but I'm have great difficulty understanding if the ESR of this cap is withing acceptable range. We chose this cap due to its sphysical size for our application.

Any help you can provide would be greatly appreciated.

Best regards,   Tim Anderson

6567.Caps-LDOs.pdf

  • 0
    TI__Mastermind 22610 points

    The part # on the top/left of the chart (EMK212BJ475KD) seems to be for 0805 not 0603. (Taiyo Yuden 4.7uF 16V 10% X5R 0805)

    You did not state the intended Vout that will be applied, and MLCC have definite a voltage derating for the capacitance value (the 4.7uF values is for 0Vdc).

    For this chart, having 0.01 ohm ESR at 100kHz with 4.7uF capacitance should be adquate. But ... if you're applying 15V and if the capacitance derates 50% to 2.2uF (just a wild guess) then probably going to be really close to the edge. But even at the edge you might have adequate performance, you won't know unless you build it and test it..

    The document you referenced is good for understanding the concept of how esr affects stability, no so much on how to pick a suitable capacitor.

  • 0 in reply to Donald Jones
    Prodigy 120 points

    Hi Don,

    As before, I really appreciate your very quick response.

    You are correct the case size is 0805 (and we would prefer an 0603)

    The LP2980IM5-3.3 is a fixed 3.3-volt output LDO. And, that brings up an excellent point that we could use a much lower voltage multi-layer cap than 16-volts. Maybe a 6.3-volt cap? Our objective is to use as small a physical sized cap as we can get away (although smaller than 0603 is pushing our pick-and-place machine) with while still having good LDO operational stability without any occilation. The Taiyo Yuden part number for a 4.7uf 6.3-volt cap (0603 case) is JMK107BJ475MK. I will have to email them for the ESR plot as it is not part of their standard tech info. If it has a similar ESR plot to the one I provided previously, is it your opinion that it should work fine for this regulator? Or, would you prefer to see the plot for the lower voltage cap first?

    Best regards and again, thank you for your help.

    Tim Anderson