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ISO1540: SDA/SCL always have pull-up power issue

Francis Jiang
Expert 3310 points
Part Number: ISO1540
Other Parts Discussed in Thread: BQ76942

Hi Team,

Currently, customer used our ISO1540 meet some corner issue:

In customer system, he add a switvh(MOS) in the line of VCC, to turn-on and turn-off ISO1540, but at the time, SDA/SCL are always pulled-up by 3.3V. So the voltage stress of SDA/SCL will reach the corner when MOS turn-off(VCC=0V), which is shown as below, it is related to VCC volt.

So whether this case has risk in the system design? Whether SDA/SCL pin will damage due to the always pull-up power?

Any further questions please feel free to contact me. Thanks in advance.

BRs,

Francis

  • +1
    TI__Mastermind 29595 points

    Hello Francis, 

    Thank you for your question. You are correct, applying 3.3V to the SDA/SCL pins with the isolator unpowered would violate the absolute maximum ratings. This can affect the long-term reliability of the isolator. It is recommended to power down the pull-up resistors when the device is unpowered. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Expert 3310 points

    Hi Andrew,

    Thanks for your reply.

    In customer system, there are 3pcs ISO1540 communication with a same BQ76942, I don't know whether we can program the address of ISO1540 in BQ76942 to distinguish them, because they are isolation I2C.

    BRs,

    Francis