ADS7138: AVDD Fluctuation

McKenna Strambi

Intellectual 1550 points

Part Number: ADS7138

Tool/software:

Hi expert,

Could you please help check the impact of AVDD fluctuation to ADS7138?

Our AVDD supply is expected to be 3.3V nominally, but down to 3.15V when with low battery or so.

I saw in the datasheet that LSB = AVDD/4096. It seems the accuracy is not far off.

Worried about if there’s something else missing here?

Thank you!

McKenna

4 months ago

0 Joel Meraz 4 months ago

TI__Genius 15420 points

Hi McKenna,

Since the ADS7138 uses AVDD as its reference voltage, a fluctuation in the supply directly impacts the measurement. Can you give me a little more details into what the issue is? Is there an error in the measurement?

Regards,
Joel

0 McKenna Strambi 4 months ago in reply to Joel Meraz

TI__Intellectual 1550 points

Hi Joel,

It’s not fabricated yet.

The application is to measure the NTC and get the temperature.

Would like to know the estimated offset or error by LSB shift or other factors.

If the error is quite small, we might get away from it as +/-1 degree Celsius is not noticeable.

Thank you!

McKenna

0 McKenna Strambi 4 months ago in reply to McKenna Strambi

TI__Intellectual 1550 points

Hi Joel,

Following up on this.

Thanks!

McKenna

0 Joel Meraz 4 months ago in reply to McKenna Strambi

TI__Genius 15420 points

Hi McKenna,

Sorry, I didn't realize a follow-up was requested. The TUE can be obtained by taking the root-sum squared of the gain error, offset error, and INL. Since these errors are min/max specd over temperature, but are uncorrelated, this is a valid method.

This blog post gives a good introduction to this:
https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/adc-accuracy-part-2-total-unadjusted-error-explained

Regards,
Joel

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ADS7138: AVDD Fluctuation