• TI Thinks Resolved

Stacking multiple digital isolators for higher isolation (e.g. ISOW7840)

Prodigy 125 points

Replies: 2

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On another support thread a TI engineer suggested potentially stacking multiple digital isolators to achieve higher isolation voltages:

e2e.ti.com/.../851658

As the voltage experienced by each one off the isolators would be directly proportional to their impedance we worry about unbalances.

Thus, some questions:
1. Are the impedances of these chips somewhat controlled? (this would give us a window of fluctuation)

2. Do you have some data on the tests performed doing that?

3. How would the powering work? Do the isolated power supplies have even higher impedance than the isolator chips? Or would they be the weakest link?
What about the ISOW7840? I imagine that one would not supply enough power to power a second unit, would it?

This could potentially be huge for us if we indeed could do that. Thus, I hope you can help.

  • Hi VVolt,

    Thank you for posting to E2E! Yes, it is possible to achieve higher isolation voltages by stacking digital isolators in series. For additional context, please also refer to the thread below:



    Our data is limited in this practice, but impedance is proportional to distribution of voltage stresses between series isolators.

    1. Device impedances and parameters are bound by the corresponding datasheet, and TI offers refined silicon processes for this consistency from device-to-device
    2. Yes; I will check if this is something I can share
    3. Power supplies can be generated by an external source, like using two SN6505 and transformer solutions, or as you said, by using two ISOW78xx in series. The available output power will decrease with each additional isolation barrier due to inefficiencies, so one ISOW78xx can power a second ISOW78xx with ~20mA - 45mA available on the final isolated output depending on switching frequencies and power supply levels.
      Isolation ratings of the power supply will vary based on which components are used, e.g. transformer vs. ISOW, but isolation ratings for digital isolators are typically higher.


    I hope this information is helpful. Please expect my follow up early next week and feel free to ask additional questions meanwhile.


    Thank you,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Hi VVolt,

    Hopefully all is well. As mentioned above, our testing indicates isolation performance improves when using isolators in series, and distribution of high-voltage stresses across them is proportional to the impedance of each device. I can share data with you directly if you send me a Request to Connect or Personal Message.


    Respectfully,
    Manuel Chavez