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Original question:

LM2907

LM2907-N: LM2907

vinay kumar41
Prodigy 120 points
Part Number: LM2907-N

frequency to volatge converter(2).xlsPAGE1.docscan0236.docscan0238.doc

Dear sir,
we want to convert the frequency input from the BLDC motor halls in to voltage for that we have use the LM2907-N but as we given input from the Function generator it has recorded as shown in the attachment but as we connected with Practical Motor it has shown the Output is Zero and not varing with the input Frequency.
we are sending the schematic and how the motor hall frequency is connected and also we are sharing the results of LM2907-N  with Function generator frequency as an input of 10vpp of square wave duty cycle 50% and hall frequency waveform and tacho input frequency waveform.

and C1=10nf.
  • 0
    Prodigy 120 points
    can you share the support engineer mail to us so we have a clear the issue we facing and we can resolve quickly.
  • 0 in reply to vinay kumar41
    Guru 140200 points

    Hi Vinay,

    you already posted this issue here, right?

    Don't connect Pin11 directly to signal ground but generate a voltage of about 0.7V at that pin, like shown in figure 22 of datasheet:

    Kai

  • 0 in reply to vinay kumar41
    Prodigy 120 points
    can you share the support engineer mail which is an reply mode so we do.
  • 0
    TI__Guru* 93105 points

    Hi Vinay,

    The BLDC motor output is referenced to ground and as Kai pointed one input of the comparator needs to be biased above 0 V when using a single positive supply. He provided the Fig. 22 example that shows the comparator inverting input being biased at about +0.7 V by a resistor and small signal diode. This needs to done or it is unlikely that the comparator will operate correctly.

    The circuit schematic that was provided is difficult to follow and appears to have incorrect connections. I went ahead and drew a simple LM2907 frequency-to-voltage circuit based on the datasheet information. If you wire your circuit as shown it should operate as expected. Since I couldn't follow the component values on your schematic I substituted some place holders for R1, R2 and C1. You can set them as needed.

    Note that we do not take E2E inquiries off line unless there is some particular privacy reason to do so.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

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

    Did my circuit suggestion for the LM2907 resolve your issue? If so, please close this E2E inquiry.

    Regards, Thomas
    Precision Amplifiers Applications Engineering
  • 0 in reply to Thomas Kuehl
    TI__Genius 11135 points
    Vinay

    We haven't heard back from you so we assume this resolved your issue. If not, just post another reply below.

    Thanks
    Dennis