SNVSBF4 November   2019 LDC1001-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Typical Application — Axial Distance Sensing
  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 Conditions
    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 Parallel Resonance Impedance and Inductance With LDC1001-Q1
        1. 7.3.2.1 Measuring Inductance
          1. 7.3.2.1.1 Example
    4. 7.4 Device Functional Modes
      1. 7.4.1 INTB Pin Modes
        1. 7.4.1.1 Comparator Mode
        2. 7.4.1.2 Wake-Up Mode
        3. 7.4.1.3 DRDYB Mode
    5. 7.5 Programming
      1. 7.5.1 Digital Interface
        1. 7.5.1.1 SPI Description
        2. 7.5.1.2 Extended SPI Transactions
    6. 7.6 Register Map
      1. 7.6.1 Register Description
        1. 7.6.1.1  Revision ID (offset = 0x00) [reset = 0x80]
          1. Table 2. Revision ID Field Descriptions
        2. 7.6.1.2  Rp_MAX (offset = 0x01) [reset = 0x0E]
          1. Table 3. Rp_MAX Field Descriptions
        3. 7.6.1.3  Rp_MIN (offset = 0x02) [reset = 0x14]
          1. Table 4. Rp_MIN Field Descriptions
        4. 7.6.1.4  Sensor Frequency (offset = 0x03) [reset = 0x45]
          1. Table 5. Sensor Frequency Field Descriptions
        5. 7.6.1.5  LDC Configuration (offset = 0x04) [reset = 0x1B]
          1. Table 6. LDC Configuration Field Descriptions
        6. 7.6.1.6  Clock Configuration (offset = 0x05) [reset = 0x01]
          1. Table 7. Clock Configuration Field Descriptions
        7. 7.6.1.7  Comparator Threshold High LSB (offset = 0x06) [reset = 0xFF]
          1. Table 8. Comparator Threshold High LSB Field Descriptions
        8. 7.6.1.8  Comparator Threshold High MSB (offset = 0x07) [reset = 0xFF]
          1. Table 9. Comparator Threshold High MSB Field Descriptions
        9. 7.6.1.9  Comparator Threshold Low LSB (offset = 0x08) [reset = 0x00]
          1. Table 10. Comparator Threshold Low LSB Field Descriptions
        10. 7.6.1.10 Comparator Threshold Low MSB (offset = 0x09) [reset = 0x00]
          1. Table 11. Comparator Threshold Low MSB Field Descriptions
        11. 7.6.1.11 INTB Pin Configuration (offset = 0x0A) [reset = 0x00]
          1. Table 12. INTB Pin Configuration Field Descriptions
        12. 7.6.1.12 Power Configuration (offset = 0x0B) [reset = 0x00]
          1. Table 13. Power Configuration Field Descriptions
        13. 7.6.1.13 Status (offset = 0x20) [reset = NA]
          1. Table 14. Status Field Descriptions
        14. 7.6.1.14 Proximity Data LSB (offset = 0x21) [reset = NA]
          1. Table 15. Proximity Data LSB Field Descriptions
        15. 7.6.1.15 Proximity Data MSB (offset = 0x22) [reset = NA]
          1. Table 16. Proximity Data MSB Field Descriptions
        16. 7.6.1.16 Frequency Counter LSB (offset = 0x23) [reset = NA]
          1. Table 17. Frequency Counter LSB Field Descriptions
        17. 7.6.1.17 Frequency Counter Mid-Byte (offset = 0x24) [reset = NA]
          1. Table 18. Frequency Counter Mid-Byte Field Descriptions
        18. 7.6.1.18 Frequency Counter MSB (offset = 0x25) [reset = NA]
          1. Table 19. Frequency Counter MSB Field Descriptions
  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
        1. 8.1.2.1 Example
      3. 8.1.3 Selecting a Filter Capacitor (CFA and CFB Pins)
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Sensor and Target
        2. 8.2.2.2 Calculating a Sensor Capacitor
        3. 8.2.2.3 Selecting a Filter Capacitor
        4. 8.2.2.4 Setting Rp_MIN and Rp_MAX
        5. 8.2.2.5 Calculating Minimum Sensor Frequency
      3. 8.2.3 Application Curves
  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 Receiving Notification of Documentation Updates
    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 Parallel Resonance Impedance and Inductance With LDC1001-Q1

Remember that the LDC1001-Q1 can determine the value of RP by monitoring the amount of power injected into the resonator. The device returns this value as a digital value which is inversely proportional to RP. The LDC1001-Q1 device can also measure the oscillation frequency of the LC circuit, which can be used to determine the inductance of the LC circuit. The oscillation frequency is returned as a digital value.

The LDC1001-Q1 device 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 maximum input range supported by the LDC1001-Q1 device. To achieve better resolution in the desired sensing range, the LDC1001-Q1 device offers a programmable input range through the Rp_MIN and Rp_MAX registers. See the Calculation of Rp_Min and Rp_Max section for how to set these registers.

When the resonance impedance of the sensor, RP, drops below the programed Rp_MIN, the RP output of the LDC will clip at the full scale output. An example occurrence of this situation is when a target comes too close to the coil.

LDC1001-Q1 tc02_trans_char_slos886.gifFigure 10. Transfer Characteristics of LDC1001-Q1 With Rp_MIN = 16.160 kΩ and Rp_MAX = 48.481 kΩ

Use Equation 3 to calculate the resonance impedance from the digital output code.

Equation 3. RP = (Rp_MAX × Rp_MIN ) / (Rp_MIN × (1 – Y) + Rp_MAX × Y), in Ω.

where

  • Y = Proximity Data / 215
  • Proximity data is the LDC output, register address 0x21 and 0x22.

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

Equation 4. Y = 5000 / 215 = 0.1526
Equation 5. RP = (38785 × 2394) / (2394 × (1 – 0.1526) + 38785 × 0.1526) =(92851290) / (2028.675 + 5918.591)
Equation 6. RP = 11.683 kΩ

Figure 11 and Figure 12 show the change in RMS noise versus distance and a histogram of noise, with the target at an 0.8-mm distance from the sensor coil. Data was collected with a 14-mm PCB coil (23 turns, 4-mil trace width, 4-mil spacing between trace, 1-oz copper thickness, FR4) with a sensing range of 0.125 mm to 1.125 mm. At a distance of 0.8 mm, the RMS noise is approximately 250 nm.

LDC1001-Q1 tc03_RMS_noise_vs_distance_slos886.gifFigure 11. Typical RMS Noise vs Distance With PCB Coil
LDC1001-Q1 tc04_histo_count_vs_deviation_slos886.gifFigure 12. Histogram of Output Codes at 0.8-mm Distance

NOTE

Although the LDC1001-Q1 device has high resolution, the absolute accuracy depends on offset and gain correction which can be achieved by two-point calibration.