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Original question:

CD40109B: Wiring of CD40109

CD40109B: Enable logic level for High-to-low level shifting

Stephen Bernhoeft
Prodigy 80 points
Part Number: CD40109B


Tool/software:

Hi

When operated in the mode VCC > VDD, the CD40109 will operate as a high-to-low level-shifter. In this situation, what are the logic levels for the "Enable" pin?

In fact I am not 100% sure what this logic level level is generally - is it (0.7* / 0.3*) Vdd for instance? I do not understand the lower part of the table "STATIC ELECTRICAL CHARACTERISTICS".
For example, the column "Vo" and the entry "1,9": What does this "1,9" signify? - I assume Vo must be short for Voltage Out.

In my case, I have 2 chips:

  1. One is acting as 5v (in) --> 9v (out).
  2. One is acting as 9v (in) --> 5v (out).

What are the ENABLE logic levels here. Is 5V fine in both cases, or does case (2) need 9V?

Regards
Stephen

  • 0
    TI__Mastermind 26530 points

    Hello Stephen,

    From my understanding is the Enable Pin is always referenced to VCC. In the two cases, you don't list VCC but I'm going to assume VCC=VIN.

    If so, Enable Pin needs to be:

    • 5V in Case 1
    • 9V in Case 2

    As for what's the Enable threshold. If you look at VIL and VIH parameters, you will see it uses a 30% * VCC and 70% * VCC, respectively. Enable will use the same thresholds. 

    I hope this helps.

    Regards,

    Josh

  • 0 in reply to Joshua Salinas
    Prodigy 80 points

    Thank you Josh.

    The part I do understand is that 1.5/5 = 0.3 and 3.5/5 = 0.7 (etc)

    I still fail to fully understand the way the information is presented though. The leftmost numerical columns have the heading "Vo", "Vcc", "Vdd" in the DS. I assume "Vo" is output voltage... Then the same 3 figures appear for the row VIL Max and the row VIH min. These values are

    "1,9"
    "1.5, 13.5"

    I do not know what these numbers are meant to convey. What does "1,9" ('one' 'comma' 'nine') indicate for instance?

    Why are these 3 values identical for both rows, and where is 13.5 from? For example, 13.5 is 70% of 19.28V, but I doubt this is the meaning intended.

  • 0 in reply to Stephen Bernhoeft
    Guru 318050 points

    The VO columns specifies the output voltages (low and high). This makes sense only for an unbuffered device; with the CD40109B, the output voltage does not depend on the analog input voltage, only on whether it is above or below the switching threshold. You can ignore this column.