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14.4V ground reference for ADC
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Arjunan M R:

--- Quote from: Siwastaja on May 30, 2019, 03:46:42 pm ---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.

--- End quote ---
Then why do manufacturers says to use lower value ceramic and also higher value tantalum together  for bypassing??
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 going to use X5R.
Simon:

--- Quote from: Arjunan M R on May 30, 2019, 04:13:55 pm ---
--- Quote from: Siwastaja on May 30, 2019, 03:46:42 pm ---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.

--- End quote ---
Then why do manufacturers says to use lower value ceramic and also higher value tantalum together  for bypassing??

--- End quote ---

Low ESR is good but too much capacitance with a low ESR can cause instability. For reasons of cost and stability usually you use a large high ESR capacitor with some ceramic. The ceramic acts fast and by the time it is depleted the electrolytic is supplying power. It's about the frequency response. A fast edge has a high frequency component although the actual main waveform frequency may be low. It's that fast edge that the ceramic deals with.

I have looked at a SMPS controller chip and it specifies that the output capacitor of 100µF must NOT be low ESR as the capacitor reacts so fast that it will make the control loop go unstable. But for good performance it wants low ESR capacitors on the input of only 2x2.2µF. You can pay £0.60 for a 100µF capacitor with 200mOhm ESR, a 28mOhm ESR capacitor is larger and costs £2.60.
Arjunan M R:
I am using a 100nF ceramic and 10uF tantalum for bypassing ADC , DAC and VRef.
Is that enough?
Arjunan M R:
 So the manufacturers says to use 10uF tantalum for frequency response and stability.
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