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CD74HCT4067-Q1: Vcc range

David D
Intellectual 580 points
Part Number: CD74HCT4067-Q1
Other Parts Discussed in Thread: CD4051B-Q1, CD74HC4067

Hi,

Due to system constraints I need to use CD74HCT4067QM96Q1 with Vcc=5.7V.

Can you please advise what are the possible implications?

Thanks

  • 0
    TI__Mastermind 27568 points

    Hey David,

    I think to properly address this question, breaking down what "Recommended" and "Absolute max" mean.
    The Recommended Operating Conditions refers to the conditions in which we can guarantee performance of the device. These values have been heavily tested and ensured to function as stated in the datasheet.
    The Absolute Maximum Ratings refer to the limits, be it voltage, current, or temperature, of the device where exceeding these limits will cause permanent damage to the device.

    The 5.7V for the CDHCT4067 you've noted lies somewhere in between and we don't recommend using this device in such a manner. The implications may not be seen immediately but the long terms affects will be there. This will reduce the life time of the device and the performance can't be guaranteed. That's to say, it may underperform in On-resistance or leakage, and the power supply draw could be expected to be higher. It would be recommended to avoid using the device in this manner. 

    What are some of the key specs that led you to this device? Can we replace it with something that may fit better?
    Admittedly the selection of 16:1 automotive devices is limited but you could use 2 of the CD4051B-Q1. It's an 8:1 Q100 qualified device. You can tie the 2 outputs together and effectively create a 16:1 that way. The supply range is wider here (up to 20V by grounding Vss)

    Let me know what you think,
    Rami

  • 0 in reply to Rami Mooti1
    Intellectual 580 points

    Hi Rami,

    Actually it's an existing design. So it has to be footprint compatible.

    How about CD74HC4067M96?

    It does allow Vcc=6V.

    Can you advise what are the key differences between the two devices?

    Regards,

    David.

  • 0 in reply to David D
    TI__Mastermind 27568 points

    David,

    These are very similar devices and the footprints are compatible so you could definitely drop it in but the key difference here is that the CD74HC4067 isn't automotive qualified. Is this a key requirement for your system? 
    Another thing to note would be the logic levels. The HC devices at 6V has VIh of 4.2V and VIL of 1.8V while the Q1 device is at 2V and 0.8V at it's highest supply respectively. When possible, the logic levels should be done at the rails, but in case that isn't feasible, it's something to note. 

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Intellectual 580 points

    Thanks a lot, Rami,

    Another option is to wire up a dedicated ~5V supply for the CD74HCT4067QM96Q1 .

    What's the maximal current the device is expected to consume at Vcc pin at worst case?

    Is it 1.8mA? The spec is a bit confusing...

    [Digital controls are driven from 5V logic, Analog inputs are 3.3V]

    Thanks,

    David.

  • 0 in reply to David D
    TI__Mastermind 27568 points

    David,

    Yes, wiring up another 5V supply would resolve this issue and provide power to the Q1 device via this.

    The 1.8mA you're referring too is the 'theoretical worst-case' for dual supply. This is confusing as this is a single sided supply device. I believe the intentions here were to list it as single sided. The conditions are listed as Vcc = 5.5V and Vi = 2.4V. So this is when operating with the widest supply but the Input voltage (on the select lines) is somewhere between the rails. As I mentioned previously, you want to keep your logic at the rails (i.e. if single sided supply Vcc = 5.5V; 5V = high logic; 0V = Low logic. This reduces the current consumption.
    With the input control voltage in the middle you'll source more current through the VDD, since the device is somewhere between the On/Off states.

    The ICC value listed in the datasheet is a good metric for the supply current. This is under the conditions of switching at the rails with Vcc=5.5V. The max Icc across temperature range is 80uA.

    Thanks,
    Rami