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ISO1228: Maximum current on field-side output

Rafael Savariego
Prodigy 60 points
Part Number: ISO1228
Other Parts Discussed in Thread: ISO1212, , ISO1211, ISOM8110, ISOM8710

Tool/software:

Hi!

I'm thinking about using the ISO1228, ISO1211 or ISO1212 in one design. In ISO1228 datasheet the maximum operating condition says that the maximum sink/source is about 3.3/4.2mA, but my application requires a minimum current of 10 - 20 mA because that is the current that the load device will consider as active state (the other side of the device in the field side is a high-side switch with a current proportional feedback pin with a large attenuation factor).

Could I add some external components to the ISO1228 to increase the maximum source/sink current per pin?

Maybe this is not the best IC for my application, I would appreciate any comments.

Thank you very much in advance.

  • 0
    TI__Mastermind 29225 points

    Hello Rafael, 

    Thank you for your question. Please allow me another day to look into this further.

    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 60 points

    Okey Andrew, thank you very much in advance.

  • +1 in reply to Rafael Savariego
    TI__Mastermind 29225 points

    Hello Rafael, 

    Thank you for your patience. The ISO1228 could not support a 10-20mA input current. The highest current limit supported would under type 2 operation. As shown in 8.2.3.1.2 Voltage Thresholds, "for Type 2 operation, it is recommended to use two channels in parallel, with RILIM = 1 kΩ and RPAR = 9.76 kΩ operation in sink mode, resulting in a current limit of 7 mA (typical)."

    One solution would be to use a discrete component like opto-emulators ISOM8710 or ISOM8110. These can either be used to isolate the digital inputs by themselves or they can be used to limit the current to the 3.5mA current limit of the ISO1228. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 60 points

    Hi Andrew,

    Thank you very much for your quick reply, I will evaluate your solution.