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| 14.4V ground reference for ADC |
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| Simon:
If it's a ceramic it's low ESR, ESR is a problem for electrolytics or niche applications with ceramic. |
| Arjunan M R:
--- Quote from: Simon on May 30, 2019, 12:52:19 pm ---If it's a ceramic it's low ESR, ESR is a problem for electrolytics or niche applications with ceramic. --- End quote --- So what are the parameters i need to look when selecting the ceramic capacitor rather than voltage and capacitance |
| Simon:
The dialectric is an indicator of the capacitors quality and tolerance. The best is X7R, the next best is X7S. All ceramics will have good enough low ESR for what you want unless you are dabling with EMC which you are not here. |
| Siwastaja:
Standard ceramic capacitor all have very low ESR, the lowest you can get practically. For a typical 0805 size, it's roughly around 10 milliohms. Compare this to around 5-10 ohms, three orders of magnitude more, for similar capacitance electrolytics, tantalum or aluminium. It's often not specified, as it's irrelevant whether it's 0, 10 or 20 mOhm, it can be approximated zero in 99% of the cases. Note that ESR has both good and bad sides to it, sometimes you want to minimize it, sometimes you absolutely need it. The most important single parameter for ceramic capacitors is actual capacitance versus DC bias voltage characteristic. This is widely misunderstood subject. Opposite to common misbelief, you can't reliably deduce this characteristic from the dielectric type (unless it's C0G/NP0); you need the actual data from the manufacturer. Sometimes the spec doesn't exist; if the actual capacitance value matters at all, ignore such capacitors. It's fair to expect it can go down to 10% of the rated C, even for "good" X7R type caps. A further complication is that often the datasheets that instruct you to use a, say, 4.7uF capacitor, already assume you use such a capacitor type with poor DC bias characteristics, but fail to tell you how much actual capacitance they actually require. So requiring "4.7uF ceramic" in a datasheet can mean less than 1uF actually, but it can mean 2uF as well, so you need to guess, or play safe and use a bigger package with known good DC bias characteristics. |
| Arjunan M R:
--- Quote from: Simon on May 30, 2019, 03:32:31 pm ---The dialectric is an indicator of the capacitors quality and tolerance. The best is X7R, the next best is X7S. All ceramics will have good enough low ESR for what you want unless you are dabling with EMC which you are not here. --- End quote --- I am not bothered with EMC. |
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