ADS124S08: AINCOM can be used for common ground?

Noriyuki Takahashi

Genius 11030 points

Part Number: ADS124S08

Hi team

Customer would like to use ADS124S08 in single end and use AINCOM as common ground like the attached.

Actually their input(voltage/current) can be 8-ch in total and they use AINCOM as common ground. Is this no problem?

Regards,

Noriyuki Takahashi

over 6 years ago

0 Joachim Wuerker over 6 years ago

TI__Mastermind 23275 points

Hi Noriyuki-san,

your attachment didn't come through.

It is no problem to use AINCOM (or actually any of the other analog inputs) as a common ground connection for the other 8 single-ended measurements.
The only thing you need to consider when using a unipolar analog supply is, that you will have to bypass the internal PGA in this use case in order to meet the input voltage range requirements of ADS124S08.

Regards,

0 Noriyuki Takahashi over 6 years ago in reply to Joachim Wuerker

TI__Genius 11030 points

Joachim,

Thanks!

I keep in mind we need to bypass the PGA in case of a unipolar analog supply.

How about in case of a bipolar analog supply? We still need to bypass the PGA?

Regards,

Noriyuki Takahashi

0 Noriyuki Takahashi over 6 years ago in reply to Noriyuki Takahashi

TI__Genius 11030 points

Joachim,

This is the attached I wanted to show you.

Regards,

Noriyuki Takahashi

0 Joachim Wuerker over 6 years ago in reply to Noriyuki Takahashi

TI__Mastermind 23275 points

You are welcome Noriyuki-san.

When using a bipolar supply, you can enable the PGA in general to measure single-ended/ground-referenced signals.
If you wanted to use Gain = 1 with the PGA enabled, all you would need is an AVSS = -0.15V to measure single-ended signals where the common negative analog input is tied to GND = 0V.

Regards,

0 Noriyuki Takahashi over 6 years ago in reply to Joachim Wuerker

TI__Genius 11030 points

Joachim

Please let me confirm just in case.

Is it OK to use PGA in case of pseudo-differential like the left bottom of the attached?

Regards,

Noriyuki Takahshi

0 Joachim Wuerker over 6 years ago in reply to Noriyuki Takahashi

TI__Mastermind 23275 points

Hi Noriyuki-san,

yes, that is an absolutely correct use case when the PGA is enabled.

But please note that the absolute voltage on AINP should not go down GND or all the way up to AVDD in order to meet the input voltage requirements of the PGA.
If PGA is enabled and Gain=1 for example, then the absolute voltage on AINP is limited to AVSS + 0.15V and AVDD - 0.15V.
The differential voltage between AINP and AINN that can be measured when AINN is connected to 2.5V is then +/-2.35V.

Regards,

Data converters

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ADS124S08: AINCOM can be used for common ground?