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analog Input module

Veeranarayana Gangula
Prodigy 110 points
Other Parts Discussed in Thread: TIDA-01333, TIDA-00764, TIDA-00170, ADS8688A, TIDA-010008, ADS8694, ADS8684, ADS8688, ADS125H02, MUX36D04, MUX509, UCC12040, SN6505B, UCC12050

Hi

We are designing Analog input module  for following requirements.

Universal Input

Channels 4

Resolution 16-bit

Accuracy ±0.1% of FSR (Voltage) ±0.2% of FSR (Current)

Input Type and Range

±150mV, ±500mV, ±1V, ±5V, ±10V, 0~150mV, 0~500mV,

0~1V, 0~5V, 0~10V,

0~20mA, 4~20mA, ±20mA

Input Impedance > 10M Ω (Voltage)

Isolation 3,000 Vrms

For above requirements we are referring TIDA-01333, TIDA-00170, TIDA-00764 designs. which is the suitable design for our requirements. Please suggest suitable reference design.

Thanks

Veera

  • 0
    TI__Guru**** 154949 points

    Hello Veera

    Good to know you are working on analog input module.

    TIDA-00170 might be a good reference to consider.

    Please be sure to use ADS8688A and connect on of the input through a gain for lower input range.(±150mV,  0~150mV,)

    ADS8688A provides the following inputs range 

    ±10.24 V, ±5.12 V, ±2.56 V, ±1.28 V, ±0.64 V 3 Description – 10.24 V, 5.12 V, 2.56 V, 1.28 V

    The input impedance is 1M. if you need more you will have to buffer and you will need to generate split rail supply.

    Please refer to TIDA-010008 for buffering, input protection and split rail power generation.

    http://www.ti.com/tool/TIDA-010008

    Also please follow the below link 

    http://www.ti.com/applications/industrial/overview.html

    You can find more info on analog input module design on factory automation and grid infrastructure sectors.

    Good luck for your design.

    Regards,

    Sreenivasa 

  • 0 in reply to Kallikuppa Sreenivasa
    TI__Mastermind 41481 points

    Hi Veera,

    In addition to Sreenivasa's comments

    • Do you have channel scan time requirements for this AI module? In other words, how much time do you have to measure each channel?
    • Are your accuracy specs at room temp (25C) or over temperature? If this is over temperature, can you provide your system's temperature range?
    • Are your inputs all single-ended (reference to GND) or do you need differential input?

    If your system is only 4-channels, we have the ADS8684 as well as the ADS8688. There are also 18-bit versions (ADS8694) if you need additional resolution for the low-voltage measurements without external gain e.g. ±150mV

    Please let us know so we can make sure you are using the correct ADC. Thanks!

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 110 points

    Dear  Bryan,

    Thanks for your reply and queries. Below are my responses for your queries.

    Query: Do you have channel scan time requirements for this AI module?

    Response: Yes, Total Scan rate/Sample rate of 4 channels is 10Hz which includes ADC settling time, Channel to Channel delay etc.,

    Query: Are your accuracy specs at room temp (25C) or over temperature?

    Response: Accuracy for temperature range of -25degC to +70DegC

     Query: Are your inputs all single-ended (reference to GND) or do you need differential input?

    Response: The Analog Input Module has to support to measure both Single ended and Differential Input. There will be common mode voltages as well. 

    Please suggest the best reference design which will meet our requirements.

    Note: In  analog module there will be 2 channel Digital input Output as well.

                  Digital Input :    (Dry Contact) 0: Open, 1: Close

                   Digital Output:  (Open collector to 30 V, 400 mA max. for resistance load)

                     Isolation 3,000 Vrms

                  Digital output has Supports 5 kHz Pules Output

                  Supports High-to-Low and Low-to-High Delay Output

    Please suggest DIO reference design as well

    Thanks 

    Veera

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 110 points

    Dear Srinivasa,

    Thanks for your response. We are going through ref design. Quick catch from design. What is the function of -15V_ISO to R78. 

  • 0 in reply to Veeranarayana Gangula
    TI__Mastermind 41481 points

    Hi Veera,

    Thanks for providing this additional information.

    Given your system requirements, the ADS125H02 would be a great option. This is a 24-bit, 40 kSPS Delta-Sigma ADC with an integrated PGA offering gains from 1/8 to 128. With this flexible PGA, the ADS125H02 can measure large inputs (up to ±15V on an ±18V supply) or very small inputs (±39 mV) and still maintain 16-bit resolution at your data rates. And, this device offers high input impedance of >1GΩ without external circuitry.

    We don't currently have a reference design using this device, but you can take a look at the ADS125H02 EVM as a good schematic and layout reference, especially with how the high voltage supplies are generated.

    Since the H02 only supports 1x differential input, you could use a 4x differential channel mux such as MUX36D04 or MUX509 at the input. The ADS125H02 has GPIO pins that can control this mux so you do not need additional control lines from your MCU.

    Let me know if you have any questions about this solution.

    -Bryan

  • 0 in reply to Veeranarayana Gangula
    TI__Guru**** 154949 points

    Hello Veera 

    http://www.ti.com/lit/ug/tidu392/tidu392.pdf

    Please refer to the specifications in the design guide. The voltage inputs are bidirectional and hence the reference is -15V.

    Regards,

    Sreenivasa 

  • 0 in reply to Bryan Lizon86
    Prodigy 110 points

    Dear Bryan,

    Thanks for your reply and inputs. This is further to your response and queries.

    Query: Are your accuracy specs at room temp (25C) or over temperature?

    Response: Accuracy for temperature is room temp (25C). In this case will you recommend ADS125H02 or any other ADC?

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 110 points

    Dear Sreenivasa,

    Thanks for detailed information. We would like test the evaluation  board TIDA-00170. Is it available for sale? If not available for sale  we will get the fabrication and PCB assembly. Could you please share the latest PCB  and fabrication files?

    TIDA-00170 design is with ADS8688.  Can we  replace  ADS8688 with ADS8688A to evaluate the ADS8688A?

    Our objective is to test the TIDA-00170 design and ADS8688A. 

    Thanks and Regards

    Veera

  • 0 in reply to Veeranarayana Gangula
    TI__Guru**** 154949 points

    Hello Veera 

    Good to know that you have finalized the devices as ADS8688A and happy to have helped you in finalizing the device.

    http://www.ti.com/tool/TIDA-00170

    We do not have the TIDA-00170 boards that we could have provided.

    In the above link, please go to the design files section and the files are available.

    Couple of suggestions

    If you are using isolated interface, i would suggest using ISO77XX family of devices that can help you optimize the design and cost. Also there are the newest family and offers better performance.

    If you are planning to have analog output and have quad channels, you could consider 

    http://www.ti.com/product/DAC8775

    Good luck for you design.

    Regards,

    Sreenivasa 

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 110 points

    Dear Sreenivasa,

    Thanks for quick reply. 

    As you suggested we will use the PCB files from  http://www.ti.com/tool/TIDA-00170.  The ADC used in TIDA-00170 is ADS8688. Can we assemble ADS8688A  in place of ADS8688 and test the TIDA-00170 design? Please clarify.

    We will use isolated interface. Not going to use analog output..

    Thanks and Regards

    Veera

  • 0 in reply to Veeranarayana Gangula
    TI__Guru**** 154949 points

    Hello Veera 

    The devices are pin compatible. Also note that if you are only using analog input, you can make many of the AO as DNP. It can save your efforts. 

    In the design you would make later, the isolated power also can be simpler. Depending on cost challenges you can use SN6505B based or UCC12040/UCC12050.

    TI provides samole support for your prototype.

    Please be sure to order the samples on TI.com for faster prototyping.

    Regards,

    Sreenivasa 

  • 0 in reply to Veeranarayana Gangula
    TI__Mastermind 41481 points

    Hi Veera,

    The H02 datasheet provides many specs at both room temperature and over temperature. In general the not drift specs (offset / gain error / etc.) are given at room temp, while the drift specs (offset drift, gain error drift, VREF drift) are provided over temperature. Most of these specifications also have min/max values, in addition to typical specs.

    -Bryan