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ISO1212: Design review for signal comparison application

ArTzy
Genius 16900 points
Part Number: ISO1212

Tool/software:

Hi Experts,

Asking your assistance on this design query from customer using ISO1212:

I aim to set up an STO circuit. The first step in the flowchart of my STO circuit is to receive two +24VDC signals from a PLC and obtain two +3.3VDC signals. I have chosen the ISO1212DBQR chip for this first step. I have reviewed the EVMs and reference designs of this chip and created the circuit attached. I would like to consult you on the following points:

  1. I apply the STO 1 EXT (+24VDC signal) to the Sense1 and IN1 pins and provide +3.3VDC to vcc1, expecting to obtain a +3.3VDC output from OUT1. Is this circuit suitable for this purpose? Based on the references I have read; I expect it to work accordingly.
  2. If I don't perform ground isolation and use a single ground, will there be any issues related to the chip's operation?

Thank you.

Regards,
Archie A.

  • 0
    TI__Mastermind 26315 points

    Hello Archie, 

    Thank you for reaching out. 

    1. Yes, the circuit should work as described. 
    2. If the Grounds are tied together as shown above the device will not benefit from the isolation (isolation barrier is bypassed, however, the device will continue to operate. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Genius 16900 points

    Thank you, Andrew.

    In the current situation, I assigned the GND label to the GND1 pin. For FGND1 and FGND2, I combined the two pins and assigned them the FGND label. However, I did not connect these two pins on the board with a trace, nor did I use isolation chips like optocouplers.

    Any issue on that design set-up?

    Regards,
    Archie A.

  • +1 in reply to ArTzy
    TI__Mastermind 26315 points

    Hello Archie, 

    Thanks for the additional information. There is not issue with tying the FGNDx pins together. Since GND1 and the FGNDx pins are on separate ground planes the device will have the proper isolation performance. The sensors for the STO 1 and STO 2 nodes should use the FGNDx pins as a ground reference. 

    Best,
    Andrew