• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 18 subscribers
  • Views 561 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

74HCT4067 input protection against power supply fault

Almerindo Paiva
Intellectual 410 points

Dear Sirs,

I would like to ask what could happen when a remote sensor is connected to HCT4067 and the board where this device is connected isn't be powered? How can I prevent this device from being demaged in this case?

Is there any channel active when there is no power?

Best regards,

Almerindo Paiva

  • 0
    TI__Mastermind 46480 points

    Do you mean the HCT4067 is not powered and you have a voltage on an input of the HCT4067?

    If this is what you mean then you should protect the input clamp diode by limiting the current to less than 20ma by a series resistor.

     

  • 0 in reply to Chris Cockrill
    Intellectual 410 points

    Hi Chris,

    Yes, that is what I mean. But the Power Supply pin accepts only 50mA. What if I have a voltage on all 16 channels? Will I have current flowing on each channel when the device isn't powered?

    Can I put a 1N4148 in the power supply pin? Will this avoid current be flowing throught the schottky diodes?

    Best regards,

    Almerindo Paiva

  • 0 in reply to Almerindo Paiva
    TI__Mastermind 46480 points

    Each pin will have a clamp diode so there would need to be a series resistor on each pin. Another thing to keep in mind is that the part will actually power up through the diode. If there is 5V on an input then Vcc will have 4.3V on it and the part will be on.

  • 0 in reply to Chris Cockrill
    Intellectual 410 points

    Dear Mr. Chris,

    Sorry to ask you again. If all channels have 5V, I need to limit the current that flows on each pin to IVddmax/16. Right?

    Suppose I have a fault, and ALL 16 channels have 20V, clamped by a TVS diode. My board has no power supply. And I have a serie 1K resistor between the my input and the MUX.

    What will happen?

    Thank you,

    Best regards,

    Almerindo Paiva