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LM5158-Q1: Output Capacitor Selection

TI-CSC
Genius 10530 points
Part Number: LM5158-Q1

Hello E2E Experts,

Good day.

I am using the LM5158QRTERQ1 in the SEPIC configuration outputting 25V. I've been trying to find a good capacitor to use for my output capacitor that also doesn't take up too much space, but it seems like most of the available ceramic capacitors have a large capacitance change rate at 25V. It mentions using a ceramic capacitor in the datasheet, but I was wondering if I can use a tantalum capacitor instead. According to the QuickStart excel sheet provided by the datasheet, I need 40uF of output capacitance to meet my desired ripple voltage, which generally either comes in a very large package or with a low voltage rating for ceramic capacitors.

The datasheet mentions using ceramic capacitors but doesn't explicitly say to not use tantalum. I am wondering if it would be ok to use a tantalum capacitor instead.

Regards,

CSC

  • 0
    TI__Genius 11215 points

    Hello, 

    Thanks for reaching out. We do recommend to have a ceramic cap at the output due to its low ESR value. In this case we might suggest to have both ceramic capacitors (of lower capacitance value but high enough voltage rating) and the tantalum one. For an output voltage of 25V, we recommend choosing ceramic caps rated for 50V, due to the derating of the cap. Let us know if you have further questions. 

    Kind regards,

    EM

  • 0 in reply to EM
    TI__Genius 13995 points

    Hey EM,

    This question was posted on behalf of my customer and we have a follow-up question for you. The main reason they were looking into tantalum capacitors was due to the derating of ceramic capacitors, but they were also worried about the higher ESR. Would using both kind of meet in the middle with lower ESR from the ceramic caps and the tantalum keeping the capacitance up?

    Thanks for the support!

    Best regards,

    Matt Calvo

  • 0 in reply to Matt Calvo
    TI__Genius 11215 points

    Hello Matt, 

    Yes, both caps (ceramic and tantalum) are needed, in this case a ceramic cap rated for 50V and low capacitance value (100nF, 1uF) and a tantalum one with big capacitance are required. In such case the system will have the benefit of low ESR and the right capacitance value. Let us know if further help is needed. 

    Kind regards,
    EM