SNOA993A June   2018  – July 2021 LDC2112 , LDC2114 , LDC3114 , LDC3114-Q1

 

  1.   Trademarks
  2. 1Introduction
  3. 2Scan Rate and Sampling Interval
    1. 2.1 Low Power Mode and Normal Power Mode
    2. 2.2 Button Sequencing and Error Handling
  4. 3Data Polarity and Timeout
    1. 3.1 Button Timeout
  5. 4Internal Algorithms Overview
  6. 5Baseline Tracking
    1. 5.1 Baseline Increment
    2. 5.2 Baseline Tracking Reset
    3. 5.3 Button Actuation Time
    4. 5.4 BTPAUSE
    5. 5.5 Fast Tracking Factor
  7. 6Gain, Hysteresis, and Threshold
    1. 6.1 Threshold and Hysteresis
  8. 7Multi-Button Algorithms
    1. 7.1 Max Win
    2. 7.2 Anti-Common Mode
    3. 7.3 Anti-Twist Factor
    4. 7.4 Anti-Deform Factor
  9. 8Summary
  10. 9Revision History

2 Scan Rate and Sampling Interval

Once the LDC211x or LDC3114 powers on, it continuously samples the enabled channels and returns to as shown in Figure 2-1. The active channels, sample time interval, and button scan rate are all configurable parameters. Refer to Table 2-1 for a listing of the device parameters that control the Scan Rate and Sample Interval. A higher Scan Rate produces a more responsive interface, but generally at the cost of higher average supply current consumption. Note that the scan rate can vary by up to ±30% from the nominal value across devices.

GUID-FA64D472-116F-4C13-91AF-42DF82EC23FE-low.gif Figure 2-1 Sample Interval and Scan Rate
Table 2-1 LDC211x and LDC3114 Sample Control
Device Parameter Configuration Effect Details
SENCYCx Button Sample Interval for channel x Each channel has dedicated setting. Sensor frequency is used to determine proper setting.
CNTSCx Button Sample Interval for channel x Each channel has dedicated setting. Sensor frequency, LCDIV, and SENCYCx is used to determine proper setting
LCDIV Button Sample interval for all channels Common setting for all channels
LPWRB pin Button Scan Interval When set High, device samples based on NPSR value. When set Low, device sample based on LPSR value.
NPSR Button Scan Interval When LPWRB pin is High, this field sets the device scan rate from 10 sps to 80 sps.
LPSR Button Scan Interval When LPWRB pin is Low, this field sets the device scan rate from 0.625 sps to 5 sps.

The Button Sample Interval is a function of the SENCYCx, LCDIV, and the Sensor Oscillation Frequency. The sample time, tSAMPLE is set by:

tSAMPLE = 128 × (SENCYCx+1)×2LCDIV ÷ ƒSENSORx

The recommended sample interval is 1 ms, as this provides a good balance on noise vs. supply current. Shorter sample intervals may have reduced SNR. Variations in sensor frequency greater than 2.5% may need to use different settings for SENCYCx. If the sensor frequency increases significantly and the SENCYCx & LCDIV settings are not changed, then a reduction in sensitivity can occur. Alternatively, if the sensor frequency decreases by ~30% from the configured frequency, it is possible for internal counters in the device to over-range, resulting in improper operation.