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VFC320: Fast-settling FVC

Fabio Cornaglia
Prodigy 10 points
Part Number: VFC320
Other Parts Discussed in Thread: VFC32, , LM331

Hi,

I'm interested into use VCF320 as Fast-settling FVC.

In my application I've a square wave signal with an input frequency ranging from 1.3KHz to 4.8KHz, coming form a magnetic pick-up sensor. The  VCF320 supply voltage is +-15V. 

I want to reach a settling time of less than 1ms, to do this I chose the following components (refer to the SBVA005 application note):

R6=36.5kOhm 1%

C3=2.2nF 1% Polystyrene

C2=3300pF NPO ceramic

Are those componets corrects?

Also I have doubts in choosing the right S/H circuit for this application, what are the main constraints for S/H? Do you have any suggestions on modern components that can be used?

Thanks in advance.

  • 0
    TI__Guru* 93105 points

    Hello Fabio,

    TI has a several V-to-F converters available including the VFC320. Some of the others are the VFC32, LM2907/2917 and LM331, but I think for your F-to-V application the VFC320 will provide the highest linearity performance. It exhibits the lowest linearity error at 10 kHz FS of the V-to-F converters listed (0.005%). The LM331 is one to consider as well.

    http://www.ti.com/lit/ds/symlink/lm331.pdf

    The component values you selected for the VFC320 should result in a settling time under 1 ms for 0.1 % settling. The 3.3 nF one-shot capacitor is recommended for an input up to 10 kHz. C3 is critical from a settling standpoint so the 1 % polystyrene capacitor is a good choice. Polystyrene capacitor exhibit a low temperature coefficient. Also, the NPO capacitor is a good choice for the one shot capacitor which isn't as critical in terms of tolerance, but can take advantage of the NPO low temperature coefficient. 

    The AB-040A, Frequency-to-Voltage Conversion - Applications Bulletin, is about as complete treatment on the subject as you will find for the VFC320. There really isn't anything that I can add in terms of additional information on the subject. 

    Regards, Thomas

    Precision Amplifiers Applications Engineering