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SN74LS92: Suggestion solution for 3.3V application

Part Number: SN74LS92
Other Parts Discussed in Thread: SN74LV4040A, CD4059A

Hi there:

I'd like to check an solution for our customer. The original reference design is SN74LS92 with VCC: 5V system.

If changing into 3.3V, any suggestion solution could achieve same function? (or I found the  SN74LV4040A this one would be OK?)

The application is G-PON system with Mainchip: Realtek)

  • Hi Kay,
    Divide-by-12 and 12-bit division are very different functions.

    This operation is typically handled by a low-cost microcontroller today ( www.ti.com/.../overview.html ). It looks like the whole purpose of the circuit is to generate a 2.048 MHz clock from a 24.576 MHz clock -- something any MCU could do very easily with minimal code. Depending on the system requirements, they might even be able to eliminate a few components with that solution.

    If they are intent on doing this with logic, there are a few options. A counter like the LV4040 that you found could be used to do the counting, then added logic can be used to force a reset when a decimal "12" is reached. That probably isn't the most efficient solution since multiple devices will be required.

    They could also consider using a divide-by-N component like the CD4059A. The CD4k family isn't the best solution at 3.3V -- it's really designed for 15V operation. Personally, I would choose either of the other two options over this one.