SNOSDC7B December   2021  – December 2021 LDC3114-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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 Digital Interface
    7. 6.7 I2C Interface
    8. 6.8 Timing Diagram
    9. 6.9 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 Multimode Operation
      2. 7.3.2 Multichannel and Single-Channel Operation
      3. 7.3.3 Raw Data Output
      4. 7.3.4 Button Output Interfaces
      5. 7.3.5 Programmable Button Sensitivity
      6. 7.3.6 Baseline Tracking
      7. 7.3.7 Integrated Button Algorithms
      8. 7.3.8 I2C Interface
        1. 7.3.8.1 I2C Interface Specifications
        2. 7.3.8.2 I2C Bus Control
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Power Mode
      2. 7.4.2 Low Power Mode
      3. 7.4.3 Configuration Mode
    5. 7.5 Register Maps
      1. 7.5.1 LDC3114 Registers
      2. 7.5.2 Gain Table for Registers GAIN0, GAIN1, GAIN2, and GAIN3
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  Theory of Operation
      2. 8.1.2  Designing Sensor Parameters
      3. 8.1.3  Setting COM Pin Capacitor
      4. 8.1.4  Defining Power-On Timing
      5. 8.1.5  Configuring Button or Raw Data Scan Rate
      6. 8.1.6  Programming Button or Raw Data Sampling Window
      7. 8.1.7  Scaling Frequency Counter Output
      8. 8.1.8  Setting Button Triggering Threshold
      9. 8.1.9  Tracking Baseline
      10. 8.1.10 Mitigating False Button Detections
        1. 8.1.10.1 Eliminating Common-Mode Change (Anti-Common)
        2. 8.1.10.2 Resolving Simultaneous Button Presses (Max-Win)
        3. 8.1.10.3 Overcoming Case Twisting (Anti-Twist)
        4. 8.1.10.4 Mitigating Metal Deformation (Anti-Deform)
      11. 8.1.11 Reporting Interrupts for Button Presses, Raw Data Ready and Error Conditions
      12. 8.1.12 Estimating Supply Current
    2. 8.2 Typical Application
      1. 8.2.1 Touch Button Design
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 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 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Tape and Reel Information

Package Options

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

8.1.2 Designing Sensor Parameters

Figure 8-3 shows that each inductive touch button uses an LC resonator sensor, where L is the inductor, C is the capacitor, and RS is the AC series resistance of the sensor at the frequency of operation. The key parameters of the LC sensor include frequency, effective parallel resistance RP, and quality factor Q. These parameters must be within the ranges as specified in the Sensor section of the Section 6.5 table. Note that the effective RP and Q changes when the conductive target is in place.

GUID-FAD36E08-1DC0-461B-8EE3-C517096A735B-low.gifFigure 8-3 LC Resonator

The LC sensor frequency defined in Equation 3 must be between 1 MHz and 30 MHz. For optimal performance, configure the sensor frequency to be greater than 3 MHz.

Equation 3. GUID-F6559DDC-A873-41CF-84CB-7D1A30C42C5A-low.gif

The sensor quality factor defined in Equation 4 must be between 5 and 30.

Equation 4. GUID-90599CDD-6DB9-45EF-80FE-9B0F376C4581-low.gif

The series resistance defined in Equation 5 can be represented as an equivalent parallel resistance, RP.

Equation 5. GUID-3AFF2B6F-4C99-4540-B5B4-007C39CF1BA8-low.gif
GUID-B655B38D-4C63-4C0E-8A4F-BBA607783BFF-low.gifFigure 8-4 Equivalent Parallel Circuit

RP can be viewed as the load on the sensor driver. This load corresponds to the current drive required to maintain the oscillation amplitude. RP must be between 350 Ω and 10 kΩ.

In summary, the LDC3114-Q1 requires that the sensor parameters are within the following ranges when the conductive target is present:

  • 1 MHz ≤ fSENSOR ≤ 30 MHz
  • 5 ≤ Q ≤ 30
  • 350 Ω ≤ RP ≤ 10 kΩ