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Capacitor ESR specification, and ESR inpact on IC's.

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David_

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Hello.

I have a REF5045, and REF2030 both voltage references.

REF5045 datasheet:
A supply bypass capacitor ranging between 1μF to 10μF
is recommended. A 1μF to 50μF output capacitor (C_L)
must be connected from V_OUT to GND.
The ESR value of C_L must be less than
or equal to 1.5Ω to ensure output stability. To
minimize noise, the recommended ESR of C_L is
between 1Ω and 1.5Ω.

So I pulled out my LCR-meter and started looking a my available capacitors, here is some values:

100Hz: 1kHz: 10kHz: 100kHz:

C = 1051nF 1024nF 971nF 938nF
ESR = 32,7Ω 3,16Ω 0,24Ω 0,02Ω

Ehmmm... The datasheet does not specify in what frequency band said ESR is in, the only thing I can see that relate to this is the noise specification. It is specified as 0,1Hz to 10Hz.

If a datasheets tells me the output capacitor should be between 1-50µF, or better jet, what if it says it must be between 1-50µF(I ask about both cases) what might happen if I put in a 100µF och 1000µF capacitor?

I guess it depends on the IC's but am I correct in stating that some devices will work with just about any values of bypass caps while some datasheets NEEDS to be followed to the letter more or less.
Say a LM317, it does not appear to matter much which value I choose, but take a look at TPS7A4701. Its datasheet paints up a image that you should take there values and guidelines seriously or it will be.

But that makes some regulators so specific in component values?
This is just a side question to the above, regards.
 

The key for understanding the output bypass capacitor requirements of voltage regulators and references is the feedback loop analysis.

Unfortunately the datasheets of said voltage references don't have sufficient information in this regard. You get an idea about feedback loop bandwidth (10 kHz range) from the step responses. This answers at least the question which ESR numbers matter.
 

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