SNVSBF7 November   2019 LDC1001

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Axial Distance Sensing Application
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Condition
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Inductive Sensing
      2. 7.3.2 Measuring RP With LDC1001
      3. 7.3.3 Measuring Inductance With LDC1001
    4. 7.4 Device Functional Modes
      1. 7.4.1 Power Modes
      2. 7.4.2 INTB Pin Modes
        1. 7.4.2.1 Comparator Mode
        2. 7.4.2.2 Wake-Up Mode
        3. 7.4.2.3 DRDY Mode
    5. 7.5 Programming
      1. 7.5.1 SPI Description
        1. 7.5.1.1 Extended SPI Transactions
    6. 7.6 Register Maps
      1. 7.6.1 Register Description
        1. 7.6.1.1  Revision ID (Address = 0x00)
        2. 7.6.1.2  RP_MAX (Address = 0x01)
        3. 7.6.1.3  RP_MIN (Address = 0x02)
        4. 7.6.1.4  Watchdog Timer Frequency (Address = 0x03)
        5. 7.6.1.5  LDC Configuration (Address = 0x04)
        6. 7.6.1.6  Clock Configuration (Address = 0x05)
        7. 7.6.1.7  Comparator Threshold High LSB (Address = 0x06)
        8. 7.6.1.8  Comparator Threshold High MSB (Address = 0x07)
        9. 7.6.1.9  Comparator Threshold Low LSB (Address = 0x08)
        10. 7.6.1.10 Comparator Threshold Low MSB (Address = 0x09)
        11. 7.6.1.11 INTB Pin Configuration (Address = 0x0A)
        12. 7.6.1.12 Power Configuration (Address = 0x0B)
        13. 7.6.1.13 Status (Address = 0x20)
        14. 7.6.1.14 Proximity Data LSB (Address = 0x21)
        15. 7.6.1.15 Proximity Data MSB (Address = 0x22)
        16. 7.6.1.16 Frequency Counter LSB (Address = 0x23)
        17. 7.6.1.17 Frequency Counter Mid-Byte (Address = 0x24)
        18. 7.6.1.18 Frequency Counter MSB (Address = 0x25)
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Calculation of RP_MIN and RP_MAX
        1. 8.1.1.1 RP_MAX
        2. 8.1.1.2 RP_MIN
      2. 8.1.2 Output Data Rate
      3. 8.1.3 Choosing Filter Capacitor (CFA and CFB Pins)
    2. 8.2 Typical Application
      1. 8.2.1 Axial Distance Sensing Using a PCB Sensor With LDC1001
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Sensor and Target
          2. 8.2.1.2.2 Calculating Sensor Capacitor
          3. 8.2.1.2.3 Choosing Filter Capacitor
          4. 8.2.1.2.4 Setting RP_MIN and RP_MAX
          5. 8.2.1.2.5 Calculating Minimum Sensor Frequency
        3. 8.2.1.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.2 Measuring RP With LDC1001

The LDC1001 supports a wide range of LC combinations, with oscillation frequencies ranging from 5 kHz to 5 MHz and RP ranging from 798 Ω to 3.93 MΩ. This range of RP can be viewed as the maximum input range of an ADC. As shown in Figure 9, the range of RP is typically much smaller than the maximum input range supported by the LDC1001. To get better resolution in the desired sensing range, the LDC1001 offers a programmable input range through the RP_MIN and RP_MAX registers. Refer to Calculation of RP_MIN and RP_MAX for information on setting these registers.

When the resonance impedance RP of the sensor drops below the programed RP_MIN, the RP output of the LDC will clip at its full scale output. This situation could, for example, happen when a target comes too close to the coil.

LDC1001 tc02_trans_char_snoscx2.pngFigure 10. Transfer Characteristics of LDC1001 With RP_MIN = 16.160 kΩ and RP_MAX = 48.481 kΩ

Use Equation 2 to calculate the resonance impedance from the digital output code:

Equation 2. LDC1001 eq02_snoscx2.gif

where

  • RP = Measured sensor parallel resistance in kΩ.
  • RP_MIN is the resistance (in kΩ) selected in register 0x02
  • RP_MAX is the resistance (in kΩ) selected in register 0x01
  • Y = Proximity Data÷215
  • Proximity data is the LDC RP output = (Contents of Register 0x22) × 28 + (Contents of register 0x21).

Example: If Proximity data (address 0x22:0x21) is 5000, RP_MIN is 2.394 kΩ, and RP_MAX is 38.785 kΩ ,the resonance impedance is given by:

Y = 5000/215 = 0.1526

RP = (38785 × 2394) ÷ (2394 × (1 – 0.1526) + 38785 × 0.1526) = (92851290 ÷ (2028.675 + 5918.591))

RP = 11.683 kΩ