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TPS82085: Using Tantalum Caps

David C
Expert 3350 points
Part Number: TPS82085

Hello,

I've got a design that uses  a TPS82085SIL, and we currently are using a 22 uF AVX 06036D226MAT2A X5R MLCC as the output bulk capacitor. We are looking to possibly swap this part out for a tantalum capacitor, and AVX  F380J226MMAAH1.

The data sheet for the TPS recommends a 22uF X7R capacitor, but doesn't mention a recommended ESR limit for the output cap. The tantalum we are looking at has ~0.2 Ohms ESR at 100 kHz, do you know if that added ESR would have an adverse effect on the power supply? 

Our input voltage is 4V, output voltage is 1.2V and max current draw for this supply is up to approximately 2 amps. We also have a bunch of MLCCs at the IC we are powering, 1 47uF and then a few 1 uF and 0.1 uF ceramics.

Regards,

David

  • 0
    TI__Guru**** 150950 points
    Hi David,

    The output impedance affects stability, ripple, and transient response. Normally, a ceramic cap is located closest to the IC to absorb the ripple current before it propagates through the output bus. Then, the bulk capacitance (usually tantalum or polymer) would be placed out on the bus.

    Since you have other ceramic caps on the bus, I am confused why you want to swap caps. This would still leave some ceramic in the design, in case the goal was to remove all the ceramic caps for some reason.

    If the goal is to get rid of that specific 22uF part number, then I recommend using another vendor's 22uF part or a 10uF ceramic. Or you could remove it and split the 47uF into 2x 22uF, located at the IC and at the load.

    200 mOhm ESR is extremely high compared to a ceramic. When moving or swapping caps, be sure and re-verify that the output voltage is regulated well enough for your load.