ADS8904B: VREF above RVDD - 0.3V

James Dupre

Part Number: ADS8904B

Hi,

For a variety of reasons, I would like to be able to use the same voltage rail (= 3.3V) that supplies the RVDD input to supply the VREF input as well. I realize this would violate the maximum recommended voltage for the VREF input according to the datasheet, but I would like to understand what impact this might have for functionality and/or performance?

Regards,
James

over 2 years ago

0 Keith Nicholas over 2 years ago

TI__Mastermind 40980 points

Hello James,

The internal reference buffer will saturate in this case, and there will be a voltage drop that changes with code, causing linearity issues, as well as increased noise. I have not tested a device in this condition, but the performance would probably be closer to a 12b converter than a 20b in this case.

If you do not want to use an additional reference, you can use a voltage divider from your 3.3V supply rail to generate a 3V or lower reference voltage at the buffer input. This approach will preserve the noise and linearity performance of the ADC, and will also provide ratio tracking to your 3.3V analog supply.

Regards,
Keith Nicholas
Precision ADC Applications

0 James Dupre over 2 years ago in reply to Keith Nicholas

Prodigy 90 points

Thank you Keith for your detailed and helpful reply.

0 Keith Nicholas over 2 years ago in reply to James Dupre

TI__Mastermind 40980 points

You are welcome!

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ADS8904B: VREF above RVDD - 0.3V