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Original question:

[FAQ] What is Current Transfer Ratio (CTR)?

ISOM8110: More details of the parameters about ISOM8110

Andrew Su
Intellectual 1645 points
Part Number: ISOM8110

Dears,

a customer want to use ISOM8110 to replace optocoupler, they are asking for more details of the parameters, such as the temp coefficient of the CTR, input current, output current, reverse current, dark current, rise time, fall time...

would you please help to share me more information about this parameter details?

thanks a lot!

  • 0
    Prodigy 140 points

    I have the same question.

  • 0 in reply to Brian McDonald
    TI__Mastermind 29595 points

    Hello Andrew (and Brian),

    Thanks for the promoting ISOM8110. Also, please note that we do have a list FAQs for Opto-Emulators that may be helpful.

    1. temp coefficient of the CTR
      1. More detailed figures will likely be ready for RTM. However, the below CTR table in 7.7 Electrical Characteristics shows CTR variance over forward current. The minimum and maximum values in each forward current are the variances characterized over temperature.  
      2.  
    2. input current and output current
      1. Opto-emulators are designed to simulate optocouplers, without the non-ideal characteristics of an LED input stage.
      2. Therefore, input current is user defined. The input current should be kept below the Maximum Input forward current (50mA) 
      3. Output current will be defined by the Current Transfer Ration (CTR). I_output = CTR * If. CTR = 120% for ISOM8110. 
        1. If an application has an input current of 2mA, then I_output = 1.2 * 2mA = 2.4mA. 
        2. Please note that optocoupler solutions typically have a CTR with a wide degree of variation. Opto-emulators offer a tight CTR that makes it easier to design for long term reliability. 
        3. (+) [FAQ] What is Current Transfer Ratio (CTR)?
    3. reverse current and dark current - can be found in 7.7 Electrical Characteristics (see below).
    4. rise time and fall time - these are available in the datasheet (7.8 Switching Characteristics).

    Let me know if this resolved your question. 
    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Intellectual 1645 points

    dear Andrew,

    thank you very much for the kindly explanation.

    "The minimum and maximum values in each forward current are the variances characterized over temperature", but as the TA=25 degree C, so i think the max and min values might be caused by the tolerance between devices rather than the temp?

    will the reverse current, dark current, rise time, fall time be affected by the temp?

    thanks! 

  • 0 in reply to Andrew Su
    TI__Intellectual 1645 points

    dear Andrew,

    it seems that the ISOM811X may replace Optocoupler directly, but the customer want to double confirm, if there is any note points when replace Optocoupler EL817? as ISOM811X seems to not be temp sensitive, still need no consideration of the affect of temp when design the parameters?

    the customer also wonder if we may provide more temp related information such as showed in the attached pictures:

     

  • 0 in reply to Andrew Su
    TI__Mastermind 29595 points

    Hello Andrew, 

    Andrew Su said:
    will the reverse current, dark current, rise time, fall time be affected by the temp?

    Unless otherwise noted, the minimum and maximum values in the datasheet are taken as worst-case values and are characterized across process, temperature and voltage. 

    ISOM811x will be a good replacement for EL817. As you have noted, ISOM811x will have less variation over temperature and since there is no LED, there is no need to design for the LED-aging effect. Typical application curves such as the ones above will be available at RTM.

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Intellectual 1645 points

    dear Andrew,

    thanks a lot!