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ISO78XX - Reliability using capacitance(ISO7841, ISO7831, ISO7821)

Hirotaka Matsumoto
Guru 27525 points
Other Parts Discussed in Thread: ISO7841, ISO7842

Hi all

Would you mind if we ask ISO78XX?

TI's Degital isolators use capacitive type.

We(Our customer) would like to know signal reliability as followings.  

<Content>
Can capacitive type isolator get static signal without ON/OFF(standing wave)?
Because, we guess that capacitive type isolator can only edge signal, for high speed signal.
If our recognition is not correct, could you let us know it?
If it is required ON/OFF, how much time is it reguired?(Or the latest time)
 
Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Intellectual 1815 points
    Matsumoto-san,
    All TI capacitive isolators including the ISO78xx will work perfectly with static signals.. You can look at "Detailed Description" section of the datasheet which explains the actual functioning in detail(pg14 in ISO7841 datasheet). Is a nutshell the input data is encoded and transmitted across the isolation capacitor with very high frequency carrier. So there is no problem in transmitting either DC or AC data.
    Regards,
    Sarangan Valavan
  • 0 in reply to SaranganValavan
    Guru 27525 points

    Hello Sarangan san,

    Thank you for your prompt reply!

    Ok, we got that you said as followings;
    "All TI capacitive isolators including the ISO78xx will work perfectly with static signals"
     
    We would like to confirm one point.
    Static signal is included continuous signal(0 or 1) like as 1s, 10s, 100s,,, of cource, is it OK?
    Because, we are worried that the datasheet P14 shows TX-pulse signals and RX-pulse signals. 

    We need your help.

    Kind regards,

    Hirotaka Matsumoto
     

  • 0 in reply to Hirotaka Matsumoto
    TI__Intellectual 1815 points
    Matsumoto-san,
    Static signal including continuous signal(0 or 1) , is OK. No issues.
    Regards,
    Sarangan Valavan
  • 0 in reply to SaranganValavan
    Guru 27525 points

    Sarangan san,


    Thank you for your prompt reply! Ok, we got it.
    We are sorry to cause you trouble, but if you have some documents(test result) which can shows that DC and AC are OK.

    We need your help.

    Kind regards

    Matsumoto Hirotaka

  • 0 in reply to Hirotaka Matsumoto
    TI__Intellectual 1815 points
    Matsumoto-san,
    DC performance is guaranteed and specified as part Electrical Char table in the Datasheet itself. For example Pg6 in the ISO7841 datasheet you can find the Icc numbers for DC operation
    Regards,
    Sarangan Valavan
  • 0 in reply to SaranganValavan
    Guru 27525 points

    Sarangan san,

    Thank you for your prompt reply.

    You mentioned that "DC performance is guaranteed and specified as part Electrical Char table in the Datasheet itself. For example Pg6 in the ISO7841 datasheet you can find the Icc numbers for DC operation".

    Exactly, the datasheet shows the Icc numbers for DC operation.
    But we are not sure that  the Icc numbers for DC operation is relation to reliability using capacitanse in case of DC input(static).
    So, could you let us know why DC performance is OK?
    If it is possible, could you let us know the mechanism in case of DC input?(only encoded and transfer with high frequency?)

    We are sorry to bother you.
    However we have to explain to our customer details.

    Kind regards

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    Expert 2585 points

    Hi, Hirotaka,

    For transferring  any kind of signal ISO78xx use OOK modulation. Please look at p,13 of ISO7842 datasheet to understand the algorithm.