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CD74HC4051-Q1: Understanding of abs value for IO pins

Chuqiang Wen
Expert 6310 points

Part Number: CD74HC4051-Q1

Hi team, 

I would like to understand the maximum rating of IO pin input voltage. I don't find a specific withstand voltage for IO pins. Should we refer to the input/output clamp current? If customer can ensure input current can be limited to <20mA, 4051 will not damage even IO voltage up to 7V? 

In customer case, they want to know if 4051 IO pins can withstand 7V under 5V VCC condition? 

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Thanks!

Ethan Wen

  • 0
    TI__Genius 11060 points

    Hi Ethan,

    I was not able to find a ABS information on the IO pins but the customer is going out of recommended specifications. The IO pins are recommended to be within the range of VEE to VCC. So in the case of the customer VCC is 5V but the IO pins are 7V is beyond the recommended specifications so the behavior of the device could lead to damage. 

    Thank you,
    Arya

  • 0
    Guru 326210 points

    The test conditions for IIK and IOK show that a current flows through the clamping diodes when the voltage goes more than 0.5 V beyond the supply rails. (This is the worst-case forward voltage of a plain silicon diode.)

    To prevent damage, you must keep the voltage within 0.5 V of VCC, or limit the current to less than 20 mA (e.g., with a series resistor).

  • 0 in reply to Clemens Ladisch
    TI__Expert 6310 points

    Hi Clemens, Arya, 

    Thanks! 

    My understanding is that when IO PIN voltage is trying to increase to VCC+0.5V, internal clamping diode will be clamped IO voltage. The max clamping current is 20mA. If there have external series resistor can limit current to 20mA. Then there should be no problem for 4051. 

    Is there any current limit resistors at internal of IO pins to limit the current within 20mA? 

    Ethan Wen

  • 0 in reply to Chuqiang Wen
    TI__Genius 11060 points

    Hi Ethan,

    There is no internal resistor that can limit the current to 20mA.

    If you are needing a device that can with stand the 7V IO voltage a good option here would be the 1308A-Q1 it is pin to pin with the CD74HC4051-Q1. This device has back-powering feature which helps with the higher IO voltage but this is a feature to protect from overcurrent situations. If the customer is needing a device that will work with 7V for the IO pins a different device will be needed. 

    Thank you,
    Arya