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CD74HC7046A: Locking circuit resolution

Art Mecina
Genius 16575 points
Part Number: CD74HC7046A
Other Parts Discussed in Thread: MSP-EXP430FR2311

Hello Guys,

Good day.

Our customer have built a locking circuit resolution of +/- 3 microseconds with the CD74HC7046A. Is it possible to reach higher resolution with this component?

Or if you have any advise on a component which can achieve a better resolution than this one, would be highly appreciated.

Thanks in advance!

Art

  • 0
    TI__Guru* 96681 points

    Hi Art,

    The time it takes to resolve a change in frequency will be directly linked to the type of low pass filter used in the circuit -- unless you mean something else by "locking circuit resolution."

    It seems that you haven't given me any details regarding the desired operation. What's the operating voltage? Input frequency? Waveform? desired output? I have so many questions. Any details you can give would be helpful.

  • 0 in reply to Emrys Maier
    TI__Genius 16575 points

    Hello Emrys,

    Good day.

    Here are the details:

    • Operating voltage: 5 volts
    • Locking Frequency: 50 Hz mains voltage
    • Output frequency: 500 kHz
    • Waveform: Square wave

    Note that the customer used R1-270K, R2-220K, C1-100PF to get 500KHZ, but have fluctuations around the frequency. He tried using an active filter, without success.

    Is there a way to improve the locking resolution or any alternative part that is better you can suggest?

    Thanks!

    Art

  • 0 in reply to Art Mecina
    TI__Guru* 96681 points

    Hey Art,

    Locking to a signal in under 3 microseconds when it only crosses zero every 10,000 microseconds seems like quite a challenge to me.  I've never seen a setup that can do that. Typically it takes a few cycles at least to get a lock.

    Have they considered using a microcontroller?  It could be programmed to monitor the AC waveform and make adjustments in nanoseconds to keep the output matched in frequency.  Many of them are available for under $0.25.

  • 0 in reply to Emrys Maier
    TI__Genius 16575 points

    Hello Emrys,

    Is there any specific microcontroller you can advise?

    Thanks!

    Art

  • 0 in reply to Art Mecina
    TI__Mastermind 28426 points

    Hi Art,

    I don't touch your requirement, could you share some details about customer needs for MCU?

    Thanks!

    Best Regards

    Johnson

  • 0 in reply to Johnson He
    TI__Guru* 96681 points

    Hi Johnson,

    The customer wants to monitor a 50 Hz sinusoidal input signal and produce a phase-matching 50 Hz square wave output signal -- within 3us accuracy.  I would do this with an ADC and some software to watch the waveform (probably just a simple lookup table) on an MCU. I imagine that pretty much any modern MCU could handle this.

  • 0 in reply to Emrys Maier
    TI__Mastermind 28426 points

    Hi Emrys,

    Yeah, Agree, I think ADC or comparator can be used for this function.

    Hi Art,

    Maybe you can try to evaluate this Lanuchpad : MSP-EXP430FR2311.

    Thanks!

    Best Regards

    Johnson