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TAS5630 input capacitors

Russell May
Intellectual 685 points
Other Parts Discussed in Thread: TAS5630

This is a continuation of the "TAS5630 abnormal failure" thread. I added the following question which was somewhat off-topic for that thread. The last paragraph below has minor corrections.

Posted by replied on 01-23-2012 10:24 AM

Steve, is there any reason not to design for X7R surface-mount ceramic (non-polar) input capacitors? They are available in 1206 and 1210 sizes and seem reasonably priced.

Posted by replied on 01-25-2012 8:48 PM

X7R caps contribute to THD at low frequencies. the TAS5630 is high performing enough that you see a difference between ceramic and electrolytic. So, we use electrolytic on the EVM. if you're not as concerned with THD, then ceramics are fine.

Posted by replied on 01-26-2012 2:38 AM

Thanks for reminding me of the distortion differences. Can you reference any objective distortion comparisons between 10uF X7R caps and tantalum caps at low frequency? The only similar comparison I have seen is at http://industrial.panasonic.com/ww/i_e/21088/smd-film-capacitor_e/smd-film-capacitor_e/data/02.html. It shows that 1uF X7R caps have less distortion than 1uF tantalum caps at about 400Hz or less. Above 400Hz, the tantalum caps are better. 50 to 400Hz is the frequency range that I am interested in, but I don't know how different the results would be for 10uF caps and TAS5630 input loads in PBTL mode.

Another thing I wonder about is leakage. I am pretty much stuck with using 16V 1206-size caps for now. Tantalum leakage rating (for Kemet T491A106K016AT) is equivalent to about 10Megohms at 20 degrees C. 10uF X7R leakage rating can be much better (100Megohms for AVX, 50Megohms for Kemet, but only 5Megohms for Murata, for examples). With about 4VDC of bias, the AVX X7R caps could be expected to have up to about 0.40-0.04=0.36uA less leakage than these tantalum caps. That could raise the TAS5630 output voltages by about 0.18VDC at room temperature. DC output voltages of all of the several EVM's I have, are a little less than half of their 48VDC supply. Lower input capacitor leakage should raise their DC outputs closer to half of the power supply voltage, which might allow very slightly higher symmetrical output voltage swings.

  • 0
    TI__Guru**** 189399 points

    Russell,

    We evaluated all this for the DRV6x series of products. We originally wanted to use ceramics, but found the THD was too high, so we were forced to change to electrolytics which had much better performance.

    Leakage is always an issue with electrolytics, you're correct on that comment.

    -d2