• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 780 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1158: ADS1158 -- Circuit Design

SHREYAS S BAGI
Intellectual 400 points
Part Number: ADS1158
Other Parts Discussed in Thread: ADS1255, ADS125H02

Hi,

We have used ADS1158 in one of our project which is configured as alternate current and voltage input channels ( 8 current and 8 voltage input). The reference design as shown below

Now I am using first input channel for 0-10V analog voltage and second channel for 4-20mA analog current.

Recommend me what to do with left over channels ( should i leave it floating ) ?

Please suggest any ADC with two channel compatibility for the same design considerations ( input voltage and input current design as shown in above figure )

  • 0
    TI__Mastermind 44680 points

    Hi Shreyas,

    Under normal operating conditions, there is no issue with allowing unused analog inputs pins to float.

    However from an ESD or RF perspective, it is generally recommended to prevent floating pins in case they were to act like small antennas, coupling the RF energy into the device.

    I have not run into any issues where floating analog input pins ever created a problem. IC pin footprints are very small and generally are not very good antennas. That being said, the analog inputs can be tied to any voltage potential between (and including) the AVSS and AVDD supplies, either directly or through a resistor. We've found that tying unused analog inputs to AVDD or (AVDD - AVSS) /2 generally results is lower leakage current than tying directly to AVSS; however, we're talking about currents on the order of nA's or less, so unless this is a concern, I would go with whichever option keeps the layout simple.

  • 0 in reply to Christopher Hall
    Intellectual 400 points

    Thank you for your response.

    Can u please answer my second question as mentioned in my previous post :

    " Please suggest any ADC with two channel compatibility for the same design considerations ( input voltage and input current design as shown in above figure ) ".

    Meaning can u suggest an alternate part for ADS1158 with only two channels ( input 1 -- 0 to 10V and input 2 --- 4 to 20mA ) having all the parameters matching with the ADS1158, retaining the same circuit as shown in previous post.

     

  • 0 in reply to SHREYAS S BAGI
    TI__Mastermind 44680 points

    Hi Shreyas,

    From the following list of multiplexed Delta-Sigma ADCs, the ADS125H02 or the ADS1255 are probably the two options I would recommend for your consideration: http://www.ti.com/data-converters/adc-circuit/precision-adcs/products.html?pqs=paqs&familyid=2019#p84=16;24&p1028=2;2&p89=Delta-Sigma&p3091=Multiplexed&p1498=Catalog&sort=p593max;desc

    When you said "having all the parameters matching with the ADS1158", there is nothing that will match exactly to the ADS1158, but are there other important parameters to your application (minimum resolution, data rate, etc.)? If you have any additional requirements that you can share I might be able to find a more specific recommendation.