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LDC1101 operation without reference clock

Burkhard Seyferth
Prodigy 90 points
Other Parts Discussed in Thread: LDC1101

Hello,

I only want to use the RP measurement function of the LDC1101 in a sensor application.

Is it possible to use the LDC1101 without a reference clock? If yes, how should I tight the CLKIN input - directly to VDD/GND

or via a resistor to VDD/GND?

Thanks.

Burkhard

  • 0
    TI__Genius 13650 points

    Hi Burkhard,

    Most applications use RP+L (metal type composition applications) or L-measurements (everything else). The reason is that L-measurements have a significantly lower tempco than RP measurements, so in many cases, L-measurement systems don't require temperature compensation.

    If you do want to go ahead with RP only, then CLKIN is not required. In this case, please tie the CLKIN pin directly to GND. 

  • 0 in reply to Ben Kasemsadeh
    Prodigy 90 points

    Hi Ben,


    Thanks for your comments. Unfortunately the data sheet of the LDC1101 has no statement concerning the behaviour without reference clock and most specifications in the data sheet were related to a reference clock .
    Background for my question is, that I must place the control CPU away from the LDC1101 and the connecting flat foil cable (FFC) has a limited number of connections. I thought I can omitting the ref clock, because I want to use LDC1101 as a proximity sensor. On start-up of the measurement procedure the target is away (or close, depending on mechanical construction) from the sensor in a home position and the CPU takes the current value from the sensor as a reference. Then the target will be moved to (or away) from sensor and I want observe the change in sensor signal. Because I know the wanted traveling way of the target (stepper driven - counting the number of steps) I can detect a slightly moving or may be a mechanical obstruction of the target. Every time the target moves back to home and the same procedure can take place on every target move. That's why I think, temperature compensation is not an issue for my application. What do you think about it?

    Regards,

    Burkhard

  • 0 in reply to Burkhard Seyferth
    TI__Genius 13650 points
    Hi Burkhard,
    the datasheet doesn't explicitly cover the RP-only mode because most customers use L-only or RP+L. The external reference clock is not required for RP-only.
    Yes, if you only want to do relative measurements, then RP may be sufficient. When using RP, the tempco is quite high but well defined (eg. resistivity of Al changes by 3800ppm/degree C).
  • 0 in reply to Ben Kasemsadeh
    Prodigy 90 points

    Hi Ben,

    Thanks for your answer.

    Are there any information on TI available for different materials about their changes in resistivity with temperature?

    I did some testing with stainless steel.

    Thanks.

    Regards,

    Burkhard

  • 0 in reply to Burkhard Seyferth
    TI__Genius 13650 points

    Hi Burkhard,

    we haven't published anything like it, but this information is usually available online for different metal types. 

    https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

    http://hyperphysics.phy-astr.gsu.edu/hbase/tables/rstiv.html