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LDC1614: Change of the IDRIVE value, doesn't affect the sensor response

xeguiluz
Prodigy 80 points
Part Number: LDC1614

Hi,

I'm having troubles with the output value variation regarding the increase of the distance.

This means that the value I get when the sensor is very close to the target versus the value I get when the target is not that close, keep constant whatever value of the IDRIVE.

This range I obtain corresponds always to a variation of 10uH, independently to the value selected for IDRIVE on each channel (I use four sensors). However, when I use the EVM, if I change the IDRIVE through your application, the span of increases. 

I have set the RP_OVERRIDE_EN, the SENSOR_ACTIVATE_SEL and the AUTO_AMP_DIS to '1'

I guess that perhaps I have left any "enabling" option disabled, but I don't find any on the datasheet.

Any light on this?

Thanks in advance,

  • 0
    TI__Mastermind 23810 points
    IDRIVE impacts the amplitude of the drive signal; it should not impact the inductance measurement unless it is set too high or too low.

    IDRIVE should be set so that the amplitude of your oscillation signal at the INX pins is between 1.2Vp and 1.8Vp. Try measuring the INx pins on your board to verify that the amplitude is correct when your target is at the minimum and the maximum range.

    Are you having an issue where you are not seeing much of a change in the inductance measurement regardless of where your target is? Are you using the coils included with the EVM, or is this using your own design?
  • 0 in reply to Clancy Soehren
    Prodigy 80 points
    Hi Clancy,

    Thanks for your answer.
    We are using our own coils, but they work different depending on the device connected (the EVM or our system) although all the register configuration values at the LDC are the same.
    The value of the Vp at the INx pins are between 1.2Vp and 1.5Vp when using the EVM together with our coils. However, when we connect them to our system, theses values go down to 120mVp -150mVp. Same configuration, same sensors, same probe configuration.
    Perhaps it might be any discrete component in our system?

    Kind regards,
  • 0 in reply to xeguiluz
    TI__Mastermind 23810 points
    That is very interesting. Here are a few question/debugging ideas.

    - Are you sure that the LDC1614 is being programmed correctly in your system? This seems like the most likely culprit. If the IDRIVE setting is too low, it could cause a low amplitude. Are you able to read back the configuration registers to double check?
    - Are there any differences in the discrete components between the EVM and your board, specifically on the INx pins to coil net?
    - Is the coil oscillating at the same frequency when using the EVM vs your system?
  • 0 in reply to Clancy Soehren
    Prodigy 80 points

    Hi Cancy,

    After some debugging and measurements at the INx output the source of the problem was that the IDRIVE registers were not well recorded. At this register there are some changing bits dinamically and this confused us.

    Thanks for your help.

    Kind regards,