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CD4044B: Vih for 3.3V supply operation

visakh gopinathan
Prodigy 20 points
Part Number: CD4044B

In the datasheet of CD4044B the input high voltage is specified for supply voltage of 5V, 10 V and 15V. But we are operating at a supply voltage of 3.3V and I would like to know the Vih for 3.3V supply.

 

Kindly suggest the solution as early as possible since its critical in performing the compatibility check in our design

  • 0
    Guru 243180 points
    There are no guaranteed values for 3.3 V.
    The noise margin decreases disproportionally with lower supply voltages (15/10/5 V → 4/3/1.5 V), so I'd expect it to be very low for 3.3 V.

    What kind of outputs are you using to drive the CD4044B's inputs? CMOS inputs have very low input currents (0.1 µA max.), so even weak CMOS outputs are able to drive them to the rails.
  • 0
    TI__Guru* 96591 points

    Hi,

    At 5V and 10V the VIH is exactly 0.7*VCC and the VIL is 0.3*VCC (which is a fairly typical in CMOS devices).

    It would be safe to assume that VIH is 0.8*VCC (2.64V), and VIL is 0.2*VCC (0.66V). I do not have specific data on this device, but these values give plenty of margin for the switching threshold.

    Ideally, you would want your input voltages to be within 100mV of the rails.  Is there something in your circuit that is limiting the input voltage range?