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8 LDC1000 on one PCB

user4571132
Prodigy 70 points
Other Parts Discussed in Thread: LDC1614, LDC1101

Hello,

I am dealing with a bit of an issue and hoping you experts could help me. 

I have designed 8 LDC1000 chips with 8 seperate sensors on one PCB. The sensors are idenctical with a ferrite,

My issue here is even if I calibrate each sensors they present to me different proximity values. 

I just measure on ONE at a time otherwise sleeping. 

Here you can see one measurement from each sensor: 

3436

2515

4955

5592

6122

4381

4638

4876

Thanks in advance for the help

  • 0
    TI__Genius 13650 points
    Hello,
    the different output code readings that you are seeing are due to two reasons: The part-to-part variation of the LDC1000 and of the sensor capacitor. For sensor capacitor, I recommend 1% C0G(NP0) type capacitors. The default RP reading would need to be stored as part of a one-time system calibration for absolute measurements using the LDC1000.

    Unless your application is for metal type identification, I recommend considering the LDC1101 as an alternative to the LDC1000. It is an improved version of the LDC1000 with significantly better part-to-part variation. Additional benefits include lower power consumption, higher speed, greatly improved measurement accuracy, easier design integration, and even lower cost. The LDC1614 may also be a suitable device, depending on the requirements of your application.

    In most cases (except metal type identification), L-measurements are more suitable than RP measurements. Please refer to this blog for details: e2e.ti.com/.../inductive-sensing-should-i-measure-l-rp-or-both
  • 0 in reply to Ben Kasemsadeh
    Prodigy 70 points

    Hello Ben and thanks for your answer,

    I would like to know more about the significant better part to part variance with the LDC1101. Because it would mean major design change for me I would like to know how big the difference is?

    And of course if it can be guaranteed in the long turn. 

    Is there any data of the part to part variance of the LDC1000 to help me calibrate default values? 

    Regards

    Leith

  • 0 in reply to user4571132
    TI__Genius 13650 points
    Hello Leith,
    the LDC1000 has a 10x higher part-to-part variation for RP measurements than the LDC1101. The LDC1101 uses an improved design which reduces the variation in the Sensor current drive. This is shown in the LDC1101 datasheet in the Sensor maximum current drive specification limits (not specified for the LDC1000).

    May I ask what the application is? Unless it is metal type identification, L-measurements may be better suited because they have a much lower temperature coefficient than RP measurements.