ZHCU623 January   2019

 

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3.2.2.1 Current Consumption/Life-Span

Figure 19 to Figure 24 show the current consumption of the patch under various settings. In the final design, the patch was configured to auto-advertise every 100 ms, and read temperature every 1 second. This places the average current consumption around roughly 230 µA, which means that the active life time of the patch was greater than 5 days after initialization on the 35 mAh battery. This greatly exceeds the 12-24 hour specifications for most wireless monitoring temperature patches available today. The design run time was confirmed by expending one of the flexible cells entirely after enabling the patch. Equation 1 shows how to estimate the patch lifetime depending on the total connection period.

Equation 1. TACTIVE= QBatt/(X(IConnected) + (1-X)IAuto)

    where

  • TActive is the runtime of the patch (in hours)
  • QBatt is the charge stored in the battery (in mAh)
  • X is the percentage of time the patch is expected to be connected to a smart device.
  • IConnected and IActive are the average current consumption (in mA) of the design when connected to a smart device, and when auto-advertising.

Table 3. Average Current Consumption

Condition Measured Current Draw Associated Figure Expected Runtime
Initial Startup 3.8 mA (Avg) for 21 µs Figure 19 N/A
During Auto-Advertisement 11.1 mA (Peak) Figure 20 N/A
100 ms (10 Hz) Auto-Advertisement 227.37 µA (Avg) Figure 21 153.93 hours, or 6.4 days
1 Sec (1 Hz) Auto-Advertisement 106.204 µA (Avg) Figure 22 329.6 hours, or 13.7 days
Connected to Smart Device 420.743 µA (Avg) Figure 24 83.2 Hours, or 3.5 days
TIDA-01624 FirstPowerUp.pngFigure 19. Start-Up Current Consumption
TIDA-01624 AutoAdv.pngFigure 20. Auto-Advertisements Peak Current
TIDA-01624 100msConversionTime_100msAutoAdvert.pngFigure 21. Average Current for 100-ms Auto-Advertisement
TIDA-01624 100msConversionTime_1000msAutoAdvert.pngFigure 22. Average Current for 1-s Auto-Advertisement
TIDA-01624 OnConnect.pngFigure 23. Current Consumption Change From Unconnected Auto-Advertisement to Connected.
TIDA-01624 OnConnect_CurrentMeasurement.pngFigure 24. Average Current Consumption When Connected to a Smart Device.