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Details on ESD protection on SN74LVC2G66?

Vi Pa
Prodigy 30 points
Other Parts Discussed in Thread: SN74LVC2G66, SN74LVC1G34, TXB0302, TXB0102, TXS0102

I am thinking about using this switch SN74LVC2G66 to switch some GPIO interfaces in order to prevent backpowering my device through the GPIO ports even when there is no power supply present to the device.

But, the datasheet indicates there is some ESD protection, but the diode situation is not indicated in the schematic diagram.  Are the protection diodes only to GND?  Or do they also go to SN74LVC2G66's Vcc?  Obviously if there are ESD diodes to the switch's Vcc then it won't prevent backpowering at all.

Vipa

  • 0
    Guru 317080 points

    As shown in section 6.3 of the datasheet, the control input allows voltage when powered off, but not the I/O ports.

    Do you need the signals to be bidirectional? If not, you can use some buffer with Ioff protection, e.g., SN74LVC1G34.

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    Hello Clemens,

    Thank you for your feedback.

    >Do you need the signals to be bidirectional? If not, you can use some buffer with Ioff protection, e.g., SN74LVC1G34.

    Unfortunately I do need the signals to be bidirectional. I agree, it sure would be a much easier problem if they were just inputs or just outputs.

    >As shown in section 6.3 of the datasheet, the control input allows voltage when powered off, but not the I/O ports.

    I don't understand this, or how you get this from section 6.3.  Or at least, I don't understand how this relates to my question.  I would be connecting my board's +3.3V supply to SN74LVC2G66's Vcc and Control pins. The goal is that if the board has a +3.3V supply, then the switch is closed. And if the +3.3V supply is off, then the switch is open.  What I don't want to happen is to somehow supply +3.3V through an externally provided GPIO signal, I fear this might happen through the ESD diodes... 

  • 0 in reply to Vi Pa
    Guru 317080 points

    Section 6.3 says that the I/O port voltage must not exceed Vcc.

    A two-channel digital switch with Ioff support would be the TXS0102, or TXB0102/TXB0302.

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    >Section 6.3 says that the I/O port voltage must not exceed Vcc.

    I understand now.

    >A two-channel digital switch with Ioff support would be the TXS0102, or TXB0102/TXB0302.

    Thanks for the suggestions - I will investigate this family.

    Appreciate the support

    -Vi