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

8.1.3 Selecting a Filter Capacitor (CFA and CFB Pins)

The filter capacitor is critical to the operation of the LDC1001-Q1 device. The capacitor should be low leakage, temperature stable, and it must not generate any piezoelectric noise (the dielectrics of many capacitors exhibit piezoelectric characteristics and any such noise is coupled directly through RP into the converter). The optimal capacitance values range from 20 pF to 100 nF. The value of the capacitor is based on the time constant and resonating frequency of the LC tank.

If a ceramic capacitor is used, then a C0G (or NP0) grade dielectric is recommended. The voltage rating should be 10 V or higher. The traces connecting the CFA and CFB pins to the capacitor should be as short as possible to minimize any parasitics.

For optimal performance, the selected filter capacitor connected between the CFA and CFB pins must be as small as possible, but large enough such that the active filter does not saturate. The size of this capacitor depends on the time constant of the sense coil, which is given by L / rs (L = inductance, rs = series resistance of the inductor at oscillation frequency). The larger this time constant, the larger filter capacitor is required. Therefore the time constant reaches the maximum when there is no target present in front of the sensing coil.

Use the following procedure to find the optimal filter capacitance:

  1. Use with a large filter capacitor. For a ferrite core coil, a value of 10 nF is generally large enough. For an air coil or PCB coil, a value of 100 pF is generally large enough.
  2. Power on the LDC and set the desired register values.
  3. Minimize the eddy currents losses by ensuring maximum clearance between the target and the sensing coil.
  4. Observe the signal on the CFB pin using a scope. Because this node is very sensitive to capacitive loading, the use of an active probe is recommended. As an alternative, a passive probe with a 1-kΩ series resistance between the tip and the CFB pin can be used.
  5. Vary the values of the filter capacitor until the signal observed on the CFB pin has an amplitude of approximately 1 VPP. This signal scales linearly with the reciprocal of the filter capacitance. For example, if a 100-pF filter capacitor is applied and the signal observed on the CFB pin has a peak-to-peak value of 200 mV, the desired 1-VPP value is obtained using a filter capacitor value that is calculated in Equation 16.

Equation 16. 200 mV / 1 V × 100 pF = 20 pF