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LM2907-N: lm2907-n

vinay kumar41
Prodigy 120 points
Part Number: LM2907-N

Dear sir,

we have testes the above LM2907-M of frequency to voltage converter with a input from frequency analyzer with an input of square wave of duty cycle 50% and a VCC of 5v with is we got an output which is varing with the frequency with an 0.0011 volts per one HZ i.e 891 Hz per one volt with an R1=100k and C1=22nf.

so we test with an practical  circuit of your unit which is an BLDC motor with a  hall frequency of 650HZ and other frequency signal of 3.81khz but we getting the output Vout=0v, which is not varing with the frequency signal which is a duty ratio of pulse waveform of 50% duty cycle.

can you please answer the above question why it is not varing the input hall Frequency of motor and can you share the schematic values which is suitable for the test.
  • 0
    Guru 140200 points
    Hi Vinay,

    can you show us a schematic?

    What LM2907 are you exactly using? The 8-pin or 14-pin version?

    How is the BLDC motor interfaced to the LM2907?

    Kai
  • 0
    TI__Guru* 93105 points

    Hello Vinay,

    Kai asks a good question regarding the LM2907 package type because the input circuit connections and behavior differs for the 8-pin and 14-pin LM2907 devices. The LM2907N is the 14-pin device, and the LM2907N-8 is the 8-pin device. There is also some mention of the LM2907-M in your inquiry. Please clarify which package you are using.

    Here is what the datasheet in the Section 9.1 Overview states regarding the input differences:

    "The LM29x7 frequency-to-voltage converter features two separate inputs to monitor the signal. In the 8-pin devices, one of these inputs is internally grounded and therefore it monitors the remaining input for zero crossings. In the 14-pin devices, both of these inputs are open and it instead detects whenever the differential voltage switches polarity. Therefore, the input comparator outputs a square wave of equal frequency to the input."

    Is the square wave signal provided by the frequency analyzer symmetrical about 0 V, i.e. does it swing positive and negative about ground? What is its peak-to-peak  amplitude? Also, what are the amplitude and waveform characteristics of the BLDC motor signal?

    If you can provide us the circuit schematic as Kai requested that will help us understand how you are applying the LM2907.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Guru* 93105 points
    Hello Vinay,

    Were you able to resolve your LM2907 issue? We would like to close out this E2E froum inquiry. Please use the green resolved button if this inquiry can be closed.

    Thanks, Thomas
    Precision Amplifiers Applications Engineering