SNOA954D November   2019  – June 2021 LDC0851 , LDC1001 , LDC1001-Q1 , LDC1041 , LDC1051 , LDC1101 , LDC1312 , LDC1312-Q1 , LDC1314 , LDC1314-Q1 , LDC1612 , LDC1612-Q1 , LDC1614 , LDC1614-Q1 , LDC2112 , LDC2114 , LDC3114 , LDC3114-Q1

 

  1.   Trademarks
  2. 1LDC Applications
    1. 1.1 Axial Sensing
      1. 1.1.1 Buttons and Keypads
    2. 1.2 Event Counting
    3. 1.3 Other Types of Sensing
  3. 2Inductive Sensing Theory of Operation
  4. 3LDC Device Feature Overview
    1. 3.1 Sample Rate
    2. 3.2 Sensor L Measurement and Reference Frequency
    3. 3.3 Sensor RP Measurement
    4. 3.4 Sensor RP (Current) Drive Capability
    5. 3.5 Switch Output Functionality
    6. 3.6 Sensor Frequency Range
    7. 3.7 Multi-Channel Sensing
    8. 3.8 Power Management
    9. 3.9 Internal Algorithms
  5. 4Device Families
    1. 4.1 Inductive Touch Devices
      1. 4.1.1 Inductive Touch LDC Recommended Applications
    2. 4.2 Multichannel LDC Devices
      1. 4.2.1 Multi-Channel LDC Recommended Applications
      2. 4.2.2 LDC1101
        1. 4.2.2.1 LDC1101 Recommended Applications
      3. 4.2.3 LDC0851
        1. 4.2.3.1 Recommended Applications
  6. 5Summary
  7. 6Revision History

3.3 Sensor RP Measurement

Some of TI’s LDC devices can measure the parallel resonant impedance (RP) of a sensor. This RP measurement can be scaled to match the range of sensor RP for an optimized measurement.

Because RP measurements are based on the resistivity of target, the measurement will vary with the temperature of the target; many metals have significant resistivity temperature coefficients (temp-co) which can introduce a change into the measurement based on the system temperature. For example, copper has a temp-co of 4300ppm/°C. If the target temperature changes by 20°C, the LDC would see an RP shift of >8%, which could be too large an error for the application.

Due to the large temp-co, RP measurements are better suited for applications which have a very limited temperature range, or where the target temperature is monitored, or where there is a need to measure the sensor energy loss, or for material composition.

The LDC1101 provides the highest RP measurement accuracy, and is recommended for any RP measurement where the sensor frequency is above 500 kHz.