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Theory of Operation
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3.2
Battery Life Calculation
For battery life calculations, TI highly recommends that the user reviews
CC2541 Battery Life Calculation
,
SWRA347
.
Comparing the power consumption of a BLE device to another device using a single metric is impossible.
For example, a device gets rated by its peak current. While the peak current plays a part in the total power
consumption, a device running the BLE stack only consumes current at the peak level during
transmission. Even in very high throughput systems, a BLE device is transmitting for only a small
percentage of the total time that the device is connected (see
Figure 6
).
Figure 6. Current Consumption
In addition to transmitting, there are other factors to consider when calculating battery life. A BLE device
can go through several other modes, such as receiving, sleeping, and waking up from sleep. Even if the
current consumption of a device in each different mode is known, there is not enough information to
determine the total power consumed by the device. Each layer of the BLE stack requires a certain amount
of processing to remain connected and to comply with the specifications of the protocol. The MCU takes
time to perform this processing, and during this time, current is consumed by the device. In addition, some
power might be consumed while the device switches between modes (see
Figure 7
). All of this must be
considered to get an accurate measurement of the total current consumed.
Figure 7. Current Consumption-Active versus Sleep Modes
10
Wireless Heart Rate Monitor Reference Design
TIDU195A – January 2014 – Revised July 2014
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