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CD74HC4046A: Clarification on CD74HC4046A to replace the reference CD4046BH

Maxime ATHEE
Prodigy 740 points
Part Number: CD74HC4046A
Other Parts Discussed in Thread: CD4046B, SN74AUC08, SN74S08

Dear team,

My customer would like to have clarification on this part, could you please assist ?

"We use the reference CD74HC4046APWR to replace the reference CD4046BH (mounted in a hybrid case being replaced). In introduction to the CD74HC4046 datasheet it is written: “The HC4046A and HCT4046A are high-speed silicon-gate CMOS devices that are compatible with the CD4046B”.

Then why the PC3OUT output of the CD74HC4046APWR circuit is called ZENER on the CD4046B circuit?

In fact this does not embarrassed us because we do not use output PC3OUT output. However when we use a reference instead of another the operations are not identical. For example, for the same values of R1 / R2 & C1, the output frequency of the VCO is not the same. Is there a look up table to match the output frequencies of the 2  references ?

Generally speaking what are the compatibilities and incompatibilities between these two components ?"

Thanks, Maxime

  • 0
    TI__Guru* 96591 points

    Hello Maxime,

    In the datasheet, it states that:

         The ’HC4046A and ’HCT4046A are high-speed silicon-gate CMOS devices that are pin compatible with the CD4046B of the “4000B” series.

    This indicates that the pinout of these devices are very similar, and in most cases can be directly replaced. As your customer pointed out, there is an obvious difference in that the HC(T)4046A devices have a third phase comparator circuit, PC3 instead of a built-in zener diode.

    These devices are not identical, however they are intended for the same applications and are of the "4046" function (PLL + VCO).

    This type of pin compatibility is common among logic devices -- for example, a "08" function is always a quadruple 2-input AND gate in the same pin configuration, however an SN74AUC08 will not work in the same applications as an SN74S08.

  • 0 in reply to Emrys Maier
    TI__Prodigy 740 points

    Hello Maier,

    Thanks for your clarification, 

    Please find an additional question from customer,

    We use the integrated circuit CD74HC4046APWR, on its data sheet it is written: "Data sheet acquired from Harris Semiconductor".

    I would like to know if your manufacturing processes are the same as those of the circuits of HARRIS?

    More generally, I would like to know if your CD74HC4046APWR integrated circuit is 100% compatible with your die now obsolete CD54HC4046H?

  • 0 in reply to Maxime ATHEE
    TI__Guru* 96591 points

    Hi Maxime,

    The military grade (aka "54") versions of devices are often very different internally from their commercial (aka "74") counterparts.  It's likely that the CD74HC4046APWR is significantly different from the CD54HC4046H. Typically the differences are in things such as redundant circuits and radiation hardened manufacturing techniques - which are obviously much more complex and expensive than those methods found in the commercial equivalent parts.

    Are you looking for a high reliability, military, or space grade PLL device?

  • 0 in reply to Emrys Maier
    TI__Prodigy 740 points
    Hello Maier,

    Please find below customer feedback to clarify their context

    We used to use CD54HC4046H in a custom hybrid integrated circuits … To reduce costs and to workaround obsolescence we now use reference CD74HC4046APWR. But with the same glue around them, those 2 components seem not to run the same way … e.g. time to lock.

    Can hardened manufacturing techniques be the cause of differences ?
  • 0 in reply to Maxime ATHEE
    TI__Guru* 96591 points
    It's possible - I don't see a specification for time to lock in the datasheet, so that might be a difference between the two that is undocumented.

    Can they share a schematic? It's very difficult to troubleshoot a circuit that I have never seen.