ZHCU623 January   2019

 

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2.4.1 Shelf Life and Active Life

The power budget for this design is based on the shelf life (inactive state) and active life (active state) requirements for the design. In the Bluetooth-enabled high-accuracy skin temperature flex patch, the CC2640R2F is configured in shutdown mode until the tactile switch (S1) is pressed and triggers the patch to wake up. Due to the overall low current consumption for the TMP117, the temperature sensor is powered using one of the CC2640R2 GPIOs. This reduces the total design shutdown current by removing the temperature sensor's shutdown current from consideration. Thus, the current consumption of the design in shutdown mode is now limited to 150 nA, which is primarily from the CC2640R2 MCU. As a result, the overall shelf life for this design is expected to be 3 years. This life span is limited by the shelf life of the battery itself and not by the charge storage.

For active life time requirements, temperature patches may be expected to operate for up to a few days after the patches are attached to a wearer. Current consumption can be reduced by limiting the frequency of measurement, and by transmitting temperature data alongside the auto-advertisement pulse. Section 3.2.2.1 shows the current consumption results for the Bluetooth-enabled high-accuracy skin temperature flex patch. If the patch is active but not connected to the wearer, the patch will auto-advertise up to 10 times a second, measure temperature at 1-second intervals, and have an expected run time greater than 5 days. When connected, the active life time is expected to be around 3 and a half days.

TIDA-01624 100msConversionTime_100msAutoAdvert.pngFigure 5. Power Meter Capture of Current Draw During 10-Hz Auto-Advertisement