ADS8688A: Question about input circuit

chandra shekara

Prodigy 230 points

Part Number: ADS8688A

Dear Sir/Madam,

In tidu365b Design , I would like to know What purpose is C23, R74 and -18V_ISO of ADC input circuit?

Could you please advise in detail

Regards

Chandrashekara

over 7 years ago

0 MCV over 7 years ago

TI__Intellectual 1340 points

Hi Chandrashekara,
These components are added to provide protection for the ADC input against surge (which is the worst case).

For further details, I would refer to the section "5.1.3 Protection for ESD. EFT, and Surge" of the users' guide which gives further guidance.

Best,
MCV

0 chandra shekara over 7 years ago in reply to MCV

Prodigy 230 points

Hi MCV,

Thank you for reply

I want one more clarification. please explain function of this circuit and how to configure circuit how it will switch current mode and voltage mode.

Thanks and Regards

Chandrashekara

0 MCV over 7 years ago in reply to chandra shekara

TI__Intellectual 1340 points

Hi Chandrashekara,

The OPTO_AN0 will switch the optomos ON/OFF depending if you are in Current/Voltage mode.

When U1 is closed, the 250R resistors is connected to the input and used to convert the current flowing in current mode into a voltage which can be converted by the ADC.

Best,

MCV

0 chandra shekara over 7 years ago in reply to MCV

Prodigy 230 points

Hi MCV,
How ADC know what input we are providing either voltage mode, current mode mean if input is not our control then what Will happen please suggest

Thanks and Regards
Chandrashekara

0 MCV over 7 years ago in reply to chandra shekara

TI__Intellectual 1340 points

Hi Chandrashekara,
The ADC has no way of knowing.

In PLC systems this has to be done either with jumper settings in the AI module or by SW running on the CPU module.
Best,
MCV

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ADS8688A: Question about input circuit