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LDC1101: Setting RPMIN for LHR Measurements

Hyuni
Prodigy 180 points
Part Number: LDC1101

Hi, I'm hyeonyeong shin

I would like to know a working method in LDC1101 datasheet 37 page.

Firstly, I coded 2 bits (ALT_CONFIG.LOPTIMAL, D_CONFIG.DOK_REPORT) to 1

second, I coded RPMIN setting bits, but, a sensor signal is changed about frequency, Vamp, inductance all.

so, I can make sure Rp setting how it fits standard up.

third, I don't understand this sentence " If multiple RPMIN values cover the Sensor Rp, use the higher current drive setting."

how can I use this equation? Rp=pi*V/4/I_drive

  • 0
    TI__Mastermind 23810 points
    The RPmin setting controls the I_drive. A larger I_drive leads to a larger sensor amplitude (as you can see in the equation). The amplitude of the sensor must stay within 0.25V to 1.25V.

    It is generally better to use as large of a signal as possible, so if two RPMIN settings would work, then you should choose the higher RPMIN setting so that the overall sensor amplitude is larger.

    I will give you an example for the equation.

    Rp = 5kOhms
    RPMIN setting = b100
    I_Drive = 75uA

    You can now rearrange the equation to solve for Vpk
    Vpk = Rp*4*IDRIVE/pi
    Vpk = (5k)*4*(75u)/pi
    Vpk = 0.48V
  • 0 in reply to Clancy Soehren
    TI__Genius 14270 points
    Hi Hyeonyeong,

    I'm going to add onto Clancy's response - you are configuring the LDC1101 for L only mode with the settings for LOPTIMAL and DOK_REPORT. In L only mode, the LDC1101 does not perform the RPMIN and RPMAX modulation automatically; it only uses RPMIN to control the sensor amplitude. You need to be within the sensor voltage range that Clancy instructed, and a higher sensor amplitude is better.

    The specific text "If multiple RPMIN values cover the Sensor Rp, use the higher current drive setting." refers to table 36. For example, let's say you have a sensor with an Rp of 2.2kOhms. While you could use the Rpmin setting of either 1.5k or 3k, the text is telling you to use the 1.5k setting for RPMIN.

    Regards,
    ChrisO
  • 0 in reply to Clancy Soehren
    Prodigy 180 points

    I see,
    I additionally have a wonder that my sensor can detect further distance when I_Drive is low current than means RPMIN setting is b000(96kOhms)

    in other words, Vpk which has large amplitude or not is not important to detect further distance.
    I think that, Is that right?

    And how can I set Rp at any frequency?

    Is that Rp when no target?

  • 0 in reply to Chris Oberhauser66
    Prodigy 180 points
    thank you CHrisO.

    I know the working method of RPMIN.

    I wondered the specific text , I dont know well
    but you have answered
    I appreciate it.
  • 0 in reply to Hyuni
    TI__Genius 14270 points
    Hello Hyeonyeong,

    The sensing range is not really improved with a larger sensor amplitude; what is improved is the SNR.

    Regards,

    ChrisO
  • 0 in reply to Chris Oberhauser66
    Prodigy 180 points
    oh I see i understand
    and so do you know a little at the sensing range is improved?