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TPS769: output capacitor

Part Number: TPS769

Team, 

My customer likes the TPS76950, however he has concerns on the requirement of 0.2 to 10 Ohm ESR for the output capacitor:

I do not use tantalums unless there is no other way. An aluminum electrolytic can meet this 10SVPS10M. But at $0.58 and its size I would rather use a MLCC. Is the ESR requirement frequency dependent or independent (meaning across the entire frequency spectrum)?

MLCC ESR varies with frequency, according to this site http://ksim.kemet.com/Plots/SpicePlots.aspx.

For the C0805C475K8PACTU and others like it, the ESR is met at near 1KHz, but then it doesn’t reach the 0.2 ohm requirement again. This cap is ~ $0.07.

The input side is straight forward.

Is it safe to use this part alone?

Should I increase the value to compensate for the small ESR? I used the Kemet site and the 0805 ESR is pretty much the same up to 10uF. Case size does not seem to impact the ESR.

Should I put a series 1 ohm with it?

Thanks!

Viktorija

  • Hi Viktorija,

    The ESR requirements for linear regulators should be met at the resonant frequency of the capacitor. This is the lowest point on the capacitor impedance curve.  Keep in mind that there will be some trace resistance between the regulator's pins and the capacitor which will increase ESR.  If your desired capacitor is still not meeting the minimum ESR requirement for the TPS769 stability, you can add an external resistor such as a 1 ohm in order to ensure that you are within the specified ESR range.

    Very Respectfully,

    Ryan