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ISO1540: what is the SCL/SDA status when device power down

Part Number: ISO1540
Other Parts Discussed in Thread: ISO1640

Dear team, 

Could you please help to check what is the status of SCL and SDA of ISO1540/1 when device is in power down mode. Are they high impendence? Or pull-down? Thanks.



  • Hi Zhizhao,

    Thanks for reaching out.

    The I/O pins SCL and SDA of ISO154x will be in high-impedance / floating when they are powered-down.
    We now have ISO1640 which is second-generation reinforced version that is pin-compatible to ISO1540. You might want to recommend this device to customer. Thanks.

    Koteshwar Rao

  • Hi Rao,

     Thanks for the quick reply and my last question is that 

    when ISO154x VCC1 power is off, but SDA1&SCL1 connect to other 3V3 power, could you help to confirm SDA1&SCL1 can keep Hi-Z at that situation? Thanks.



  • Hi Lucas,

    The absolute maximum rating of SDA1 and SCL1 are VCC1+0.5V, as stated in the datasheet. This means that, if VCC1 is 0V then SDA1 and SCL1 can only be applied a maximum of 0.5V. This means that the I/O pins cannot be applied with a signal without VCC1 powered otherwise, it will lead to device damage. This is also true to most other digital isolators. Thanks.

    Koteshwar Rao