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CD4046B: Toggling Output State

TI-CSC
Genius 11090 points
Part Number: CD4046B
Other Parts Discussed in Thread: TS12A12511, SN74LVC1G3157,

Hello E2E Experts,

Good day.

I've been using this device for over 40 years mainly as a V-to-F converter.

I put a voltage on pin 9 and monitor the frequency of the square wave on pin 3. 

Is there a way to assure that when the input voltage is zero, that the output will also be at zero (i.e... the bottom of the waveform)?

Currently, I isolate my external circuit through a capacitor but would like to eliminate this if possible.

Additional information: What I’m trying to do is avoid draining. Any current from the circuit when there’s no voltage on the input. I’m doing that now with a .22 µF capacitor at the output, but it gives a distorted waveform for the speaker that I’m using. Is there any way to force the output to go to zero ground state through one of the pins, so I can use the output directly through a resistor .

Thank you in advance.

Regards,

CSC

  • 0
    Guru 281410 points

    See the CD4046B application report:

    You are supposed to use pin 5.

    If the VCO is not inhibited, R2 ensures that it oscillates even with a 0 input.

  • 0 in reply to Clemens Ladisch
    TI__Genius 11090 points

    Hello Clemens,

    Good day.

    Do I have to inhibit and uninhibit pin 5 to make the v-F function?

    The way m using this is to have a variable resistance above the 500k pot to Vcc.

    Dial the pot into a useable auditory range.

    Placing a resistance here instantly generates the square wave output.

    When  I remove the resistance, I want pin 2 to be at 0 volts. Is there a way to make pin 5 go high after removing the resistance?

    Regards,

    CSC

  • 0 in reply to TI-CSC
    Guru 281410 points

    The inhibit pin disables the VCO, but the VCO output might stop in either the high or the low state. (I do not know what you're doing with the phase comparator; please show a schematic.)

    As far as I can see, the CD4046B itself cannot put its output into a known state. Use a comparator to generate the inhibit signal; you can use the same signal to control a switch (e.g., SN74LVC1G3157, TS12A12511) to disconnect the output.