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ISO7721: disable the ISO7721 in the case of a critical error

Jan Bock
Intellectual 2750 points
Part Number: ISO7721
Other Parts Discussed in Thread: SN74LVC1G17

Hi Team, 

can you please advise in the request below:

We want to disable the ISO7721 in the case of a critical error on the device.

This is currently done by cutting the power supply on the HV side of the chip. The turning off is done by MCU.

The problem we are seeing is that the voltage present at the TX ISO pin is enough to power the ISO7721 over the resistor and the internal clamping diode of the chip.

We would like to avoid increasing the resistance on the TX ISO line as this could limit our transfer speed.

 Have you encountered this problem from one of your customers? And do you have any recommended solutions to avoid this problem?

thanks 

Jan

  • +1
    TI__Guru 54245 points

    Hi Jan,

    Thanks for reaching out.

    Yes, the inputs have bypass diodes for ESD protection on pins and hence, they end up powering the device is supplied with voltage when VCC is not applied. This is currently the case with all our digital isolators and we do not have devices that can accept input signals when power is not applied.

    This can be addressed in two ways.

    1. To also disconnect / float input pins when power is disconnected.
    2. To use a buffer with failsafe input pins which can withstand input signals even when input power is disconnected and do not turn on the device. An example device is SN74LVC1G17.

    Let me know if you have any questions, thanks.


    Regards,
    Koteshwar Rao