Analog Reference Circuit

[DrNO]

Hello All,
I had a quick question about the analog reference voltage circuit in the XS1-U8A data sheet. I noticed that they give three example circuits 1. With and XTAL, 2. With an Oscillator and 3. The bare minimum. I noticed that the third one is using a PI-Filter to remove high frequency noise from the ADC Reference Voltage Pin instead of a separate 3.3V regulator.

Can anyone comment on the downfall of this approach vs. adding another 3.3V regulator as they did in the 1st and 2nd example circuits?

After looking at the two options from a size/cost perspective, they would both take up about the same amount of space however the PI-Filter would be cheaper. So will the ADC be that much more inaccurate if I use a PI-Filter?

Thank you!

[EdB]

The separate LDO is required if you intend to use the USB, otherwise the LC filter can be used.

If size is an issue then I would recommend a dual LDO (e.g. Micrel MIC5321) for both the IO and ADC power supplies.

[DrNO]

I guess a second LDO it is! Thanks for the help!