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CD74HC4067: Internal protection diodes inside CD74HC4067 or CD74HCT4067?

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Replies: 4

Views: 54

Part Number: CD74HC4067

Hi guys,

are there protection diodes inside that CMOS devices? Which max. current are they capable if there are some? 

The question is if I need external protection diodes due to over voltage above 5.5V.

Thanks,

Markus

  • The absolute maximum ratings imply that there are diodes. (See [FAQ] Can the input voltage (Vi) to my logic device be higher than the supply voltage (Vcc)?)

    The limit (which you should stay away from) is 20 mA.

  • In reply to Clemens Ladisch:

    Hi Clemens,

    ok thanks - so you mean the statement "DC Input Diode Current, Iik +/-20mA" at the abs max Ratings tells it. 

    There is written  "for Vi > Vcc + 0.5V". Does that mean I also could go up to Vi = 10V if the current is e.g. just 1mA? 

    Normally the datasheets only writing Vccmax = e.g. 5V + 0.5V allows not more voltage :-s

    BR,

    Markus

  • In reply to Marks Greulich:

    If there is a means to limit the current (typically, a series resistor), then the diode will clamp the voltage at the pin, and the chip will not actually see 10 V.

  • In reply to Marks Greulich:

    Hi Markus,

    As Clemens has mentioned when using a series limiting resistor it helps prevent the part from damage by reducing current and how the voltage will not see the same high voltage. For this part that is +/-20mA. However one of the consequences of adding larger current limiting resistors is that you can add to the insertion loss of the switch system which may not be suitable for all applications. In the case where there may be more current present than the +/-20 mA external protection devices would be suggested.

    Best,

    Parker Dodson