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LM2907-N: Non-AC input signal

Lance Bantoto
Prodigy 20 points
Part Number: LM2907-N
Other Parts Discussed in Thread: VFC32, LM331

Hello,

Does this part work for a non-AC input signal? I am trying to convert a DC input signal that swings from 0-3V from frequencies 15-225Hz at a 50% duty cycle.

This is the datasheet of the part I am using: the 0-12V signal goes through a voltage divider circuits that steps down the range to 0-3V which then goes into this IC.9687K21 Flow Meter Spec. Sheet.pdf

  • 0
    TI__Guru* 93105 points
    Hello Lance,

    It sounds like you need to convert a dc input level to an square wave output whose frequency is proportional to the input level. The LM2907-N is a frequency to voltage converter so it provides the opposite function. The device that does a voltage to frequency conversion is a called a referred to as a voltage to frequency converter, or VFC.

    Take a look at the datasheet for the VFC32. It is configurable as a V-to-F, or an F-to-V converter. The Application Information section starting on page 5 of the datasheet tells how to set the component values for the full scale input voltage, and a corresponding full scale output frequency. You can find the VFC32 datasheet here:

    www.ti.com/.../vfc32.pdf

    Note that for a VFC when the input voltage is zero, the output frequency will be zero. It shouldn't be possible to have a minimum output frequency of 15 Hz with a zero volt input level. Therefore, it may be necessary to apply an input offset is a 15 Hz output is needed.

    Regards, Thomas

    Precision Amplifiers Applications Engineering
  • 0
    TI__Guru* 93105 points
    Hi Lance,

    In addition to the VFC32, there is the LM331 VFC. You can find the datasheet here:

    www.ti.com/.../LM331

    Regards, Thomas
    Precision Amplifiers Applications Engineering
  • 0 in reply to Thomas Kuehl
    Prodigy 20 points
    Hi Thomas,

    The DC input signal is already a square-wave output. My bad. It is a 50% duty cycle square wave that swings from 0V to 3V. Will the LM2907 work?
  • 0 in reply to Lance Bantoto
    TI__Guru* 93105 points
    Hi Lance,

    Yes, the LM2907-N should work just fine with the 0 to 3 V square wave input in an F-to-V application. Follow the datasheet and application note for guidance. You can find the app note here:

    www.ti.com/.../snaa088.pdf

    Regards, Thomas
    Precision Amplifiers Applications Engineering