VFC110: Not able to get a clock output

Hi Josh, 

Josh Hollyer said:

Any suggestions for how to get this circuit to work?

Could you check the voltages and waveforms with scope and/or DMM to verify the signals at pin3, pin5, pin6 and pin11/pin12? If you are not Enable pin5, then you may not get the output frequency. Please let me know what you got so far. 

Please make sure that you are using linear power supply with adequate bypass filters. If you are using switching power supply at ±15Vdc, please filter out unwanted switching noises with low frequency LPFs (RC filters or LC filters). 

Please send me your drawing and/or bench setup images. 

Best,

Raymond

Hi Raymond. I got it able to clock but I am having an issue with the duty cycle. I want the duty cycle to always be 50% since I want to use this chip to clock an ADC, but when I change the input voltage the lower 0V value seems predefined by Cos, which means as I increase the voltage that lower part stays the same. Any idea how to fix this so I can get a proper square wave output?

Hi Josh, 

Josh Hollyer said:

I want the duty cycle to always be 50% since I want to use this chip to clock an ADC,

The frequency is a function of input voltage and the VFC110 is not going to generate DC =50% response based on the internal topology. It may be possible to generate 50% duty cycle with the additional comparator circuit. 

What frequency ranges do you need for the application? Can you work with LM555, NE555 or LTC555 timer? 

https://www.ti.com/lit/an/sboa574/sboa574.pdf?ts=1710787092387&ref_url=https%253A%252F%252Fwww.ti.com%252Fsitesearch%252Fen-us%252Fdocs%252Funiversalsearch.tsp%253FlangPref%253Den-US%2526searchTerm%253D555+timer%2526nr%253D1514

Best,

Raymond