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CD74HC4046A: question

Part Number: CD74HC4046A
Other Parts Discussed in Thread: SN74LVC1G17

Hi Experts,

My customer has question as follows. Would you please answer them?
1. This device can work well when the input frequency of SIGIN and COMPIN is 30Hz?
2. Can this device work well as a following condition?
- VCOIN, R1 and R2 connect to GND.
- C1 is open.

Best Regards,
Fujiwara

  • Hello Fujiwara-san,

    Yes, the device can function with a 30 Hz input signal, but note that the inputs require fast edges (500ns max transition time at 4.5V supply). If the input signal has slower edges, it should be put through a signal conditioning stage first, such as a Schmitt-trigger buffer (SN74LVC1G17 is an example).

    It should be noted: to get below 100 Hz, R1 must be larger than the recommended value in the DC characteristics table, and C1 must be relatively large (~10nF).

    The limitations for R1, R2, and C1 are listed in the datasheet to maintain the given specifications -- R1 and R2 must be larger than 3kohm but smaller than 300kohm, There is also a note that indicates that the parallel combination of R1 and R2 (R1*R2/(R1+R2)) should exceed 2.7kohm -- do not short R1 or R2 pin to ground.

    R2 can be left open to have zero frequency offset (infinity ohms). This is identified in numerous test conditions in the datasheet.

    C1 can be essentially any value, even left open.