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CD4044B: Can CD4044B work at 3.3V power supply?

user4356333
Prodigy 50 points
Part Number: CD4044B
Other Parts Discussed in Thread: SN74AHC00, SN74AHC02

Though the  recommended operating conditions specified in the datasheet indicates it can work between 3V and 18Volt. But all the parameters in the datasheet seems to be tested based on 5V/10V/15V power supply. I am not sure if it can work reliably at 3.3V. If so, the input and output levels are still CMOS compatible? For example, the VIL(max) should be 1V and VIH(min) should be 2.3V when powered by 3.3V? Thanks.

Kevin

  • 0
    Guru 294870 points

    It does work at 3.3 V, but none of the electrical characteristics are guaranteed.

    VIL and VIH could be extrapolated from the other values. With a lower gate voltage, the output current is probably rather small, and you should drive only high-impedance CMOS inputs. I will not try to estimate the maximum frequency.

    It would be a better idea to use an R/S latch from some other logic family, or to construct one out of two NAND gates.

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    Thanks for your reply. Could you please advise an equivalent part to CD4044B? I try to search R S latches on TI's website, but did not see any other RS latches. 

    Thanks.

    Kevin 

  • 0 in reply to user4356333
    Guru 294870 points

    There appears to be no 3.3 V RS latch, so your only choice is NAND gates.

    How many latches do you need? What frequency? Do you require Schmitt-trigger inputs, or 3-state outputs?

  • 0 in reply to Clemens Ladisch
    Prodigy 50 points

    I need 4 latches. What I want to do is to use a latch or similar IC to latch a major fault like over current, over voltage etc. When a fault occur, I hope a latch can keep the fault until a reset signal clears it. So the schmitt-trigger inputs and 3-state outputs are unnecessary for me. Thanks.

    Kevin

  • 0 in reply to user4356333
    Guru 294870 points

    Four latches requires eight NAND gates. Use two SN74AHC00‍s.

    If you want active-high inputs, or NOR gates instead (SN74AHC02).

    In any case (even with the CD4044B), you need to take care to reset the latch when powering up. (See [FAQ] What is the default output of a latched device? (Flip-Flop, latch, register))