AN92584 Datasheet, PDF (25/42 Pages) Ramtron International Corporation – Designing for Low Power and Estimating Battery Life for BLE Applications

Designing for Low Power and Estimating Battery Life for BLE Applications
4.3
4.3.1
Techniques for Increasing Battery Life
From these equations, it is evident that battery life can be increased by using the following approaches to reduce the
average current consumed:
 Reduce the Active mode current: The sensing and processing functions contribute equally, if not more, to the
overall system current consumption. Therefore, you should take a system view and reduce the current
consumption in all active operations such as sensing, data processing, and BLE transactions.
 Reduce the active time: Reduce the time spent in CPU or RF operations so that the system can be in the idle or
OFF states more often. The current consumed in these idle or OFF states is as important as the current
consumed during active operations. The current consumption in these states should be reduced by using the
available low-power modes.
The following is a list of suggestions to reduce the average current in PSoC 4/PRoC BLE devices and effectively
increase the battery life.
Reducing the Active Current
Operate at Lower CPU Clock Frequency
The application should be designed to allow the CPU to operate at lower clock frequencies to reduce the current. For
example, power-optimal algorithms and implementations tuned to the CPU architecture should be used to reduce the
processing power required for sensor data processing.
Shut Down Unused Resources
The application can put the unused peripherals and clocks into the available low-power modes permanently. In
addition, peripherals and clocks that are not required often or that are required only in specific usage modes should
be put into their lowest power modes, wherever possible.
For example, you can turn the ILO OFF for most BLE applications. The WCO can be used for all LFCLK
requirements such as the watchdog timer or BLESS.
Utilize Chip-Level Integration
Integration of the sensing circuit and other external interfaces in a single chip reduces the overall system current
consumption due to improved performance, reduced I/O switching, and communication overheads. PSoC 4 BLE is a
highly integrated device that includes Cypress CapSense^®, programmable analog with 12-bit ADC, four opamps with
comparator mode, two low-power comparators that can operate in the Deep-Sleep mode, a programmable digital
block, and up to 32 GPIOs multiplexed with different communication interfaces such as I²C, SPI, and UART. This
system integration must be utilized to reduce the external components that need to be present on a PCB for the
application and improve the overall system-level current consumption.
4.3.2
Reduce Transmit Power
Most applications require 0-dBm RF transmit power. However, the transmit power can be lowered if the device is
designed to work for ranges of less than 5 m. This reduces the RF current consumption. For example, by operating
the device at –6 dBm, the transmit current can be reduced by 3 mA.
Reducing the Active Time
Schedule Activities Around the Connection Event
The application should align the sensing and data processing operations to the beginning or end of BLE connection
events. The application can then complete all the processing and put the system into the Deep-Sleep mode along
with the BLESS until the next BLE connection event. This is more power efficient than processing asynchronous to
the BLE events, because it allows the system to be in the Deep-Sleep mode for longer times (refer to Figure 1).
However, note that the application activity should be avoided during the BLE events when the BLESS is transmitting
or receiving packets. This reduces the peak current consumption that adversely impacts the battery life of some types
of batteries such as coin-cell batteries.
Lower Sensor Scan Rates
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Document No. 001-92584 Rev. *A
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