SNOA943 January   2016 FDC2112 , FDC2112-Q1 , FDC2114 , FDC2114-Q1 , FDC2212 , FDC2212-Q1 , FDC2214 , FDC2214-Q1

 

  1.   Power Reduction Techniques for the FDC2214/2212/2114/2112 in Capacitive Sensing Applications
    1.     Trademarks
    2. 1 Duty-Cycling
      1. 1.1 FDC2x1x Operational Parameters That Affect Duty Cycling
    3. 2 Clock Gating
    4. 3 Test Setup
    5. 4 Measurement Results
      1. 4.1 Measurements with Gated Clock
    6. 5 Current Consumption Measurements vs Data Conversion Time
      1. 5.1 Data Readback Overhead
    7. 6 Comparison of Measured and Estimated Current Consumption
      1. 6.1 Estimating Current Consumption
    8. 7 Results
    9. 8 Summary

5.1 Data Readback Overhead

The FDC2214 does not retain its conversion results when in sleep mode. Because of this, the device cannot be put into the sleep state until the channel conversion measurements have been read by the microcontroller. Therefore, the data registers must be read while the device is still running in active mode which results in a fixed power consumption overhead. From the data given in Table 4, the data readback time is 0.688 ms. This overhead has a greater impact on conversion times in that order of magnitude, in this instance, at lower RCOUNT values where the data conversion times are less than 10x the data readback time.

Table 4. The Effect of Data Readback Overhead on Device Active Time

RCOUNT Data Conversion Time
(tS+tC+tSD)
(ms) 		Readback Time
(tRB)
(ms) 		Data Conversion Time
+
Data Readback Time (ms)
500 0.212 0.688 0.9
1000 0.412 0.688 1.1
5000 2.012 0.688 2.7
10000 4.012 0.688 4.7
20000 8.012 0.688 8.7
30000 12.012 0.688 12.7
40000 16.012 0.688 16.7
50000 20.012 0.688 20.7