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Original question:

TINA/Spice/LM231: lm231

LM566 VCO,

Paul Svatik
Prodigy 10 points

Is there a trick to get the LM566 square wave output to oscillate at 50% duty cycle?

  • 0
    TI__Guru 71516 points

    Hi Paul,

     I believe you are asking about the LM556, not LM566, is that correct? 

    Regards,

    ~Leonard   

  • 0
    TI__Guru 50176 points

    Hello Paul,

    The LM566 is a discontinued device, so we can only offer very limited support.

    The datasheet shows a typical duty cycle of 50%, so it is possible.

    What supply voltage, frequency and control voltage range are you using? Split or single supply? Schematic?  Do you have any scope photos?

    One common mistake using these devices is attempting to "over-modulate" by using a large modulation index (trying to vary the frequency too much). 'Bending" the frequency too much can distort the output waveform. You should not try to deviate more than 10% if you want low distortion.

    Also note there is a valid modulation input voltage range of 3/4 Vcc to Vcc for linear operation, so make sure your input voltage is within this range (may require level shifting).

    Also see An-146, which uses the LM566 as a carrier current FM transmitter. Note the limited modulation range. It also shows how to tuse the LM566 in a single supply application.

     http://www.ti.com/lit/an/snaa087/snaa087.pdf