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Need data protection not necessarily isolation Ok to use same supply both sides (replacing opto-iso)?

Category: Hardware
Product Number: ADuM242D

Question re: ADUM7442ARQZ-RL7 (or 242D)

    • ‘LINE’ refers to physical wires between PCBs
    • 1st PCB supplies power & ground to 2nd PCB over 4-conductor cable: Pwr, Gnd, Tx & Rx.
    • Line lengths <100m
    • Speeds < 230Kb
      Main purpose is data line protection
      (1) Is it ok to use same supply & ground for both (isolated) sides of a single iCoupler device?
      For PCBs, we normally use Optocouplers for data line isolation.
      We found iCoupler tech as an alternative. Problem is all references only show two separate & isolated power supplies. We need to isolate/protect data channels only. Can Vdd1 be tied to Vdd2 and Gnd1 tied to Gnd2, where Vdd ranges 3-5VDC? Does that, in any way compromise the protection of the data lines? We are focused on this need to isolate two data lines:

    (2) A second development effort requires data line level shifting - we HAVE found this sample circuitry, but again, none with the grounds tied together between the two PCBs. Is that okay?

    Hope these are easy & quick for you!

  • Hi, 

    Tying planes together will defeat the isolation. The two sides of the isolator will need to be supplied with independant supplies. 

    The isolator will operate as a level shifter with the ground planes tied together. This does however defeat the isolation. So yes, it can be done but likely a more economical level shifters can be found. 

    Regards.

    Jason

  • Thank you jnaso!

    I was aware that we lose the power isolation - but not knowing the internals - I questioned if data lines would still benefit from the electrical isolation protection?

    The alternatives are a Transorb or an RClamp type device. Would the iCouplers provide better protection plus offer level shifts if needed?     

  • Hi, 

    The ADuM24xE/D has two independent die that each sit on their own paddle. Pins 1-8 and pins 9-16 are galvanically separated, but if you make a connection between the 2 sides of the isolator, the galvanic isolation is defeated at the system level. The isolator can't offer protection if the design shorts the isolation barrier.

    Inside the device are planar, air-core transformers. Each channel has an encoder and decoder to pass data from one side to the other. There is Figure 19 and 20 in the datasheet that show the transmission scheme. 

    Regards,

    Jason