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3 way isolation for field interface modules

Shrikant Lokhande
Intellectual 655 points

Other Parts Discussed in Thread: TPS54062, ADS1120, TIPD125, DAC8750, XTR116

Hello All,

I intend to design a signal conditioning card for various field signals where I need to give standard 3 way isolation as shown in block dia. :

Input of the card will be 4-20mA signal from various transducers and output should be isolated 0-10V signal.

Here, my main concern is size and cost which I need to restrict to as low as possible.

One possibility can be using small DC-DC converters but it becomes a costly design.

I would appreciate your help if you have worked on something like this and share your ideas with me.

Thanks and Regards

shrikant. 

  • 0
    TI__Guru 64575 points

    Hi Shrikant,

    To achieve any sort of power efficient voltage isolation you'll require an isolated switching converters to create the isolated supplies for the isolated input and output modules.  This is very standard practice in this type of design and I would recommend that you consider the TPS54062 or similar devices to achieve the isolated supplies.  

    I would recommend the ADS1120/1220 for the input module and a simple external shunt resistor and input filter to acquire the 4-20mA signal.  The digital signals can be isolated from the main power-module and controller using an ISO7641 digital isolator.

    The output module can be very simply designed with the DAC8750/7750 or by using a DAC and op-amp as shown in TIPD125:   http://www.ti.com/tool/TIPD125

    Also, consider looking through TI's collection of  reference designs:

    http://www.ti.com/general/docs/refdesignsearch.tsp?DCMP=tidesigns-en&HQS=tidesigns-appstab-en

  • 0 in reply to Collin Wells
    Intellectual 655 points

    Dear Collin,

    Thanks for the quick and valuable reply.

    I will go through these datasheets and try to build a schematic which will satisfy my requirements. I will get back to you with upadate on this.

    Also I forgot to update you on our last discussion regarding 'Two XTR116 current loops using nonisolated power supply'.
     I have built the system as discussed and tested it up to full scale and system works fine.

    Regards

    Shrikant