SNOSDD0 December   2021 LDC3114

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

Package Options

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

8.1.6 Programming Button or Raw Data Sampling Window

The sampling window is the actual duration per scan cycle for active data sampling of the sensor frequency. It is programmed with the exponential parameter, LCDIV, in Register LC_DIVIDER (Address 0x17), and the individual linear sensor cycle counter SENCYCn (n = 0, 1, 2, or 3) in Registers SENSORn_CONFIG (n = 0, 1, 2, or 3, Addresses 0x20, 0x22, 0x24, 0x26). For most touch button applications, the button sampling window should be set to between 1 ms and 8 ms. For sampling rate of 160 SPS, the window has to be less than 6.25 ms. For continuous sampling, the data becomes available at the configured sampling window period rate. The recommended minimum sensor conversion time is 1 ms. Longer conversion time can be used to achieve better signal-to-noise ratio, if needed. The active channels in Figure 8-6 will sample sequentially if multiple channels are enabled.

GUID-7D37ABAA-0AB9-4611-820E-522C2B00EC4D-low.gifFigure 8-6 Configurable Scan Rate and Sampling Window

The LDC3114 is designed to work with LC resonator sensors with oscillation frequencies ranging from 1 MHz to 30 MHz. Equation 7 calculates the exact definition of the sampling window.

Equation 7. GUID-616F317C-0D90-48AA-895A-2AD8F69A6238-low.gif

where:

  • tSAMPLE is the sampling window in µs
  • SENCYCn and LCDIV are the linear and exponential scalers that set the number of sensor oscillation cycles
  • fSENSORn is the sensor frequency in MHz

In Equation 7, LCDIV (0 to 7, default 3) is the exponential LC divider that sets the approximate ranges for all channels, and SENCYCn (0 to 31, default 4) is the linear sensor cycle scaler that fine-tunes each individual channel. Together they set the number of sensor oscillation cycles used to determine the sampling window.

For example, if the LC sensor frequency is 9.2 MHz, and it is desirable to get 1-ms sampling window, then this can be achieved by setting SENCYCn = 17 and LCDIV = 2.

Alternatively, from the sampling window and sensor frequency, the LCDIV can be read off from Figure 8-7Figure 8-7. For example, 1-ms sampling window and 9.2-MHz sensor frequency intersect in the region closest to where LCDIV = 2. Then SENCYCn can be calculated accordingly.

GUID-0BAD9B67-2E22-40B2-8627-5AC3A6C38316-low.gifFigure 8-7 LCDIV as a Function of Sensor Frequency and Button Sampling Window