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Original question:

ISO7740: Enable propagation delay

ISO7740: When VCCO=5V, Enable pin is high level=3.3V, is the output normal?

Eggsy Pang
Expert 4985 points
Part Number: ISO7740

Hi Team,

          My customer plan to use ISO7740 enable pin. VCCI = 3.3V, VCCO=5V. 

We have questions, when giving 3.3V to enable pin,  is the output normal? 

Thanks!

  • 0
    TI__Genius 17100 points

    Hi Eggsy,

    Thank you for posting to E2E! HIGH level inputs to the ISO77xx are defined as a ratio of > 0.7 x VCCO. For VCCO = 5V, 3.3V is just below this threshold (3.5V) so not guaranteed for normal output. However, since the Enable pin is active by default, the ISO7740 output will be normal whether EN = VCCO or is left floating.

    Is our customer able to leave the Enable pin floating instead of connecting 3.3V?

    Thank you for your time,

    Manuel Chavez


    PSA: Post edited to clarify that the ISO77xx Enable pins are active by default

  • 0 in reply to Manuel Chavez
    TI__Expert 4985 points

    Hi Manuel,

    Thanks for your help!

    Customer need use EN pin, they will PD EN pin by default. When MCU ready, they will let EN pin go high.

     

  • 0 in reply to Eggsy Pang
    TI__Genius 17100 points

    Hi Eggsy,

    Is there a way our customer can turn the pin off instead of sending the 3.3V "HIGH" signal? A 5V HIGH signal is preferred, but an internal pull-up resistor can connect enable to VCCO if the pin is disconnected or high impedence.


    Please let me know,
    Manuel Chavez