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ISO7821: About Malfunction

ttd
Mastermind 8760 points
Part Number: ISO7821
Other Parts Discussed in Thread: ISO721

Dear Technical Support Team,

<Question 1>
Malfunction (reversal of output logic) assuming that there is no abnormality in the input signal or power supply voltage
Please let me know if there are any factors that may cause it.
We understand the risk of malfunction at CMTI> 150kV / us.
For example: 　

strong electric field over xxx kV/m

strong magnetic field on xxx μT

under xxx  input signal  dv / dt

I find following documentation about old digital isolator . Is it useful for ISO7821?

Digital Isolator E-Field Sensitivity

https://www.tij.co.jp/lit/an/slla267/slla267.pdf?ts=1649839141374&ref_url=https%253A%252F%252Fwww.google.com%252F

ISO72x Digital Isolator Magnetic-Field Immunity

https://www.ti.com/lit/an/slla181b/slla181b.pdf?ts=1649900867212

<Question 2>
I would like to know in detail the signal transmission method and principle to the extent that it can be disclosed.
(How to maintain the output H when the input signal is H, etc.)
From this content, it is best to say that the malfunction factor is limited to the unrealistic mode if CMTI is satisfied.

I see this documentation and this is useful for understanding signal transmission method

1.2 On-Off Keying (OOK) Based Communication
www.ti.com/.../slla284d.pdf


<Question 3>
If there is a document that compares the malfunction tolerance with a magnetically coupled isolator or a signal transmission method using pulse transformer.
Would you please provide it? In particular, it is desirable to have comparative materials with the pulse transformer method.

Best Regards,

ttd

  • 0
    TI__Guru 55885 points

    Hi,

    Thanks for reaching out, please find below my inputs to the questions you have listed out.

    ttd said:
    <Question 1>
    Malfunction (reversal of output logic) assuming that there is no abnormality in the input signal or power supply voltage
    Please let me know if there are any factors that may cause it.

    Violation of datasheet recommended operating conditions or specifications can affect the functioning of device. This includes CMTI as well, like you pointed out. Device supports 100kV/µs minimum CMTI and any noise faster this could affect the output.

    The device can sustain external radiations of upto 15V/m when directly exposed but if the device is in an enclosure or in applications board / end-equipment, the pass levels can be much higher.

    The device has very high immunity to magnetic field. The application note you pointed out (SLLA181) which talks about magnetic field immunity refers to older device families, but is equally applicable to ISO7821 as well.

    ttd said:
    <Question 2>
    I would like to know in detail the signal transmission method and principle to the extent that it can be disclosed.

    The application note that you pointed out (SLLA284) describes the operating principle of OOK modulation scheme. The same description is also provided in ISO7821 datasheet. Although it is a small section, it covers the operating principle of OOK modulation scheme especially because it is simple modulation scheme to understand. I believe this section is complete, please do let me know if you have any other specific questions on it.

    ttd said:
    <Question 3>
    If there is a document that compares the malfunction tolerance with a magnetically coupled isolator or a signal transmission method using pulse transformer.

    Sorry that I do not have any comparison data between capacitive, magnetic isolators and pulse transformer especially in regards to malfunction tolerance. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Mastermind 8760 points

    Hi Koteshwar Rao,

    Thank you for your reply and  I'm sorry for my reply.

    It would be helpful if you could theoretically explain why TI isolators are resistant to magnetic fields.

    You said:

    The device can sustain external radiations of upto 15V/m when directly exposed but if the device is in an enclosure or in applications board / end-equipment, the pass levels can be much higher.

    ⇒There is external radiation, but is it the electric field strength from the unit(V/m)?

    You said:

    The device has very high immunity to magnetic field. The application note you pointed out (SLLA181) which talks about magnetic field immunity refers to older device families, but is equally applicable to ISO7821 as well.

    ⇒Is the OOK method better than the edge-based ISO721 about magnetic field immunity ? If the OOK method has better magnetic field immunity, it would be helpful if you could provide documents.

    Best Regards,

    ttd

  • 0 in reply to ttd
    TI__Guru 55885 points

    Hi TTD,

    Thanks for your response.

    ttd said:
    It would be helpful if you could theoretically explain why TI isolators are resistant to magnetic fields.

    The devices that are made up of large inductive circuits are usually prone to external magnetic fields. TI capacitive isolators do not use much of inductance in the circuit and hence, do not get impacted by by external magnetic fields. The internal circuitry does have parasitic inductances but they are usually are small and compensated. Hence, no impact of external magnetic field on device.

    ttd said:
    ⇒There is external radiation, but is it the electric field strength from the unit(V/m)?

    Yes, electric field and external electrical radiations are the same things. They are measured in V/m.

    ttd said:
    ⇒Is the OOK method better than the edge-based ISO721 about magnetic field immunity ? If the OOK method has better magnetic field immunity, it would be helpful if you could provide documents.

    Since neither OOK nor edge-based devices rely on inductive designs, there is no impact of external magnetic field on these two devices equally. Both are equally immune to external magnetic fields.

    I hope this answers your further questions, thanks.


    Regards,
    Koteshwar Rao