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

7.3.3 Measuring Inductance With LDC1001

LDC1001 measures the sensor’s frequency of oscillation using a frequency counter. The frequency counter timing is set by an external clock applied on TBCLK pin. The sensor frequency can be calculated from the frequency counter register value (see registers 0x23 through 0x25) in Equation 3:

Equation 3. LDC1001 eq03_snoscx2.gif

where

  • ƒSENSOR is the measured sensor frequency
  • ƒEXT is the frequency of the external clock.
  • FCOUNT is the value obtained from the Frequency Counter Data registers (address 0x23,0x24,0x25).
  • RESPONSE_TIME is the programmed response time (set in the LDC configuration register, address 0x04).

Use Equation 4 to determine the sensor inductance:

Equation 4. LDC1001 eq04_snoscx2.gif

where

  • C is the parallel sensor capacitance
  • ƒSENSOR is the sensor frequency calculated in Equation 3

Example: If ƒEXT = 6MHz, RESPONSE_TIME = 6144, C = 100 pF and measured Fcount = 3000 (dec) (address 0x23 through 0x25)

ƒsensor=(1/3) × (6000000/3000) × (6144)= 4.096 MHz

Using the ƒsensor = 4.096 MHz example for Equation 4, the sensor inductance L = 15.098 µH.

NOTE

The accuracy of a measurement largely depends upon the frequency of the external time-base clock (TBCLK). A higher frequency will provide better measurement accuracy. The maximum supported frequency is 8 MHz.