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Original question:

VFC32 question

VFC32: VFC32 usage in Application of generating output frequency from 60Hz to 120Hz

Sadashiva Kamath
Expert 1165 points
Part Number: VFC32
Other Parts Discussed in Thread: LM331

My requirement:

  1. Application: Voltage to Frequency converter
  2. Input voltage: 0 to 3.3V (varied using potentiometer tuning)
  3. Output frequency: 60Hz to 120Hz

-------------

I have gone through TI's Voltage to Frequency converter  voltage to frequency converter devices. I see that only one IC, VFC32 is SMD and all others are having DIP packages.

Question-1:

  1. I just want to know when VFC32 is manufactured? Is this during 1990s or earlier?  Is this recommended for new designs?

 

Question-2:

  1. Can I operate VFC32KU/2K5 with Vcc=12.5V and –VCC = 0V?
  2. What is recommended R1, C1 & C2 values for my application
  3. fOUT can be connected with 3.3V pull-up resistor?


  • 0
    TI__Guru* 93105 points

    Hello Sadashiva,

    Regarding your questions:

    I have gone through TI's Voltage to Frequency converter  voltage to frequency converter devices. I see that only one IC, VFC32 is SMD and all others are having DIP packages.

    Question-1:

    1. I just want to know when VFC32 is manufactured? Is this during 1990s or earlier?  Is this recommended for new designs?

    The VFC32 is a legacy product that was introduced by Burr-Brown (acquired by TI in 2000) in the 1980s. Because of the unique V-to-F function it provides it remains in current production and is used by many customers.

     Question-2:

    Can I operate VFC32KU/2K5 with Vcc=12.5V and –VCC = 0V? - No, the VFC32 requires dual supplies for correct operation.

    1. What is recommended R1, C1 & C2 values for my application - R1 for lower frequencies is normally set to 40 kilohms. C1 and C2 are set using the information provided in datasheet Figure 2. The VFC32 is usually applied over a wider frequency range than you indicate (120 Hz max?) Just as an example, Figure 2 indicates that for an fFS of 1 kHz, C1 = 33 nF and C2 = 10 nF. You could use the equation shown for C1 and extrapolate the C2 curve for the C2 value at 120 Hz.
    2. fOUT can be connected with 3.3V pull-up resistor? It appears that it is best to keep the fOUT sink current to a maximum of 7 to 8 mA. If VPU is 5 V and RPU is 3.3 kilohms, then IPU would be 1.4 mA and that should be fine.

    The LM331 is another V-to-F converter and it will operate with a single supply, but it looks like it is only available in the DIP package.

    Regards, Thomas

    Precision Amplifiers Applications Engineering   

  • 0 in reply to Thomas Kuehl
    Expert 1165 points

    Thanks Thomas for detailed response. It is quiet useful..!!!

    Our product will be in field for min. 10-15 years.

    Is output frequency is dependent on capacitor value? Is output frequency varies over the years due to aging of capacitors over 10+ years? Also, Capacitor value changes over operating temperature (10 degC to 60 degC).

    On the other side, Is it better to consider microcontroller based Analog to Frequency converter for new designs in which we don't have such large variables that controls output frequency?

  • 0 in reply to Sadashiva Kamath
    TI__Guru* 93105 points

    Hello Sadashiva,

    Interesting, we have received a couple of inquiries regarding the longevity plans for our VFC products the last few days. Even though the VFC32 is a legacy product it fills a unique analog application niche. The product is completely viable and in full production. I can assure you there is no immediate plan to discontinue the current VFC products.

    It is listed in the VFC32 Characteristics table that FOUT = VIN / (7.5 R1 C1). Thus, the capacitor value is a direct factor in determining the output frequency from the V-to-F converter. The accuracy and quality of the capacitor need to be considered for a long term use application. Film capacitors are often very good, but a good quality C0G capacitor is likely acceptable. A study of the capacitor types and characteristics would be necessary to make the best choice.

    I don't have experience with the Analog-to-Frequency converters. If it is digitally controlled and uses a crystal based clock, then I would think it should provide good stability across the years of use.

    Regards, Thomas

    Precision Amplifiers Applications Engineering