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Original question:

LDC1101: LDC1101 / LHR RPMIN Setting

LDC1101: Setting RPMIN in LHR mode

Alex Moreland
Prodigy 80 points
Part Number: LDC1101

In LHR mode, how do you set RPMIN if the sensor RP isn’t covered entirely by a single RPMIN setting as shown in Table 36.

  • Our sensor is predicted to be: 2.01 kOhm <= Sensor Rp <= 7.07 kOhm.
  • The 3kOhm setting covers 2.1 to 6.5 kOhm
  • The 6kOhm setting covers 4.2 to 13.1 kOhm

  • 0
    TI__Mastermind 40295 points

    Alex,

    The datasheet advises that if multiple RPMIN values cover the Sensor RP, use the higher current drive setting (sec. 9.1.11).

    Based on this, you might try using the 3kOhm setting for all conditions for the LDC1101.

    If you use this approach, be sure to confirm the sensor voltage is within the guidelines (0.25Vpk to 1.25Vpk).

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 80 points

    Right. Maybe I'm misunderstanding the datasheet but in our application multiple RPMIN values don't "cover" the Sensor Rp range. The 3kOhm setting partially "covers" the range (it doesn't cover beyond 6.5 kohm and our sensor goes up to 7.07 kOhm) whereas the 6 kOhm setting also only partially "covers" the range (it doesn't cover below 4.2 kOhm but our sensor goes down to 2.01 kOhm).

    Now if our sensor Rp was between 4.2 and 6.5 that would be a different story and I would clearly pick 3 kOhm because two RPMIN settings cover the entire range but I'm told to use the higher current drive setting.

    Maybe I'm putting too much stock in the definition of the word "cover" but it doesn't make sense to me how it's worded and that is why I'm trying to understand.

  • 0 in reply to Alex Moreland
    TI__Mastermind 40295 points

    Alex,

    Its intended to set the current drive level for the sensor and keep the recommended sensor voltage range, and it is parsed into different ranges to accommodate this. 
    For a wider range, simply pick the setting that needs the highest current drive, remembering to monitor the sensor voltage and be sure it doesn't fall outside of the recommended range.  

    Regards,
    John