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Original question:

ISO7740: Secondary side output outputs H level shortly when the secondary sode power is powered up. Is this no irregular...

ISO7740: Can the H level pulse at powered up be removed?

Kazuya Nakai59
Guru 20130 points
Part Number: ISO7740

 Hello guys,

 One of my customers is evaluating ISO7740(no F version) for their new products. At the evaluation, they observed that a short pulse (micro second order) was output from ISO7740 output when ISO7740 was powered up.

 I'd like to know if there is any countermeasure to remove the short pulse. If there is any countermeasure, could you please tell me it? Is it only way to remove the short pulse to replace ISO7740 with ISO7740F? 

 Your reply would be much appreciated.

 Thank you and best regards,

 Kazuya. 

  • 0
    TI__Expert 6955 points

    Nakai -san,

    What are the states of the inputs during power on? What is the power sequence that the customer is doing? For example, Vcc1 is powered first then Vcc2. 

    Respectfully,

    Lucas Schulte

  • 0 in reply to Lucas Schulte9
    Guru 20130 points

     Hello Lucas,

     Thank you for your reply.

     The input level of the device primary side is L level at the device powered up. VCC1 and VCC2 power up timing almost same.

     But the customer uses ISO7740 (no F version) now. The device default output is H level.

     The customer expects the output of the secondary side doesn't output "H" level at powered up.

     Probably I think there is not any countermeasure to remove short H pulse. is my understanding correct?

     Thank you again and best regards,

     Kazuya.

     

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 49495 points

    Hi Kazuya-san,

    Thanks for sharing the inputs that Lucas had requested.

    Like we discussed in another E2E post (link below), after power-up the output of ISO7740 will first go to default state for a few µs and then will start following the input. If input is held LOW while output is powering up then yes, it is expected to see a small positive pulse at the output. The best way to address this is to use ISO7740F or make the input same as default state (HIGH in this case).

    Let me know if this answers your question, thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Guru 20130 points

     Hi Rao,

     Thank you very much for your reply.

      I understood that the best way to remove the output high pulse was replacing ISO7740 with ISO7740F.

     Thank you again and best regards,

     Kazuya.