AN92584 Datasheet, PDF (2/42 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
The second section provides a system-level view of a BLE device and shows how to estimate its battery life. Tips and
tricks to reduce the average current consumption and improve the battery life are discussed and illustrated with the
help of two example use-cases: a heart-rate monitor and a remote control. The current consumption in the non-BLE
parts of the system and the idle time between BLE operations adds significantly to the average current consumption.
2 Design and Implementation for Low-Power BLE
It is important that you first understand the different clocks and power modes available in PSoC 4/PRoC BLE devices
that should be managed to conserve power.
2.1 System Clocks
The PSoC 4/PRoC BLE clock system includes the following clock sources:
Two internal clock sources:
 3-MHz to 48-MHz internal main oscillator (IMO) ±2 percent across all frequencies with trim
 32-kHz internal low-speed oscillator (ILO) ±60 percent with trim
Three external clock sources:
 External clock (EXTCLK) generated using a signal from an I/O pin
 24-MHz external crystal oscillator (ECO)
 32-kHz watch crystal oscillator (WCO)
The five clock sources and the clocks derived from these sources are shown in Figure 1.
Figure 1. PSoC 4/PRoC BLE System Clocks
WCO
ILO
ECO
IMO
EXTCLK
Prescaler
/2ⁿ (n=0..2)
Divider
/2ⁿ (n=0..3)
Prescaler
/2ⁿ (n=0..7)
Low-Frequency Clock to WDT, BLE Low-
Power Logic, LCD, CPU Timer and UDB
To BLE Link Layer
To Flash and Peripherals that
Need Specific Divided Clock
To CPU & Bus Interface
of Peripherals
Clock Enables to SCB, CSD, TCPWM,
Divider 0
LCD, PASS & UDB to Divide HFCLK
/2ⁿ (n=0..16)
0-9
Divider 9
/2ⁿ (n=0..16)
Fractional Divider0
/( 2^m+(2ⁿ-1)/2ⁿ )
(m=0..16, n=0..5)
Fractional Divider1
/( 2^m+(2ⁿ-1)/2ⁿ )
(m=0..16, n=0..5)
LFCLK
LLCLK
HFCLK
SYSCLK
PER0_CLK
PER15_CLK
Table 1 summarizes the clock sources, their use in the system, and specific system constraints on them. The table
also lists the APIs that are used to turn ON or OFF the clock sources.
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Document No. 001-92584 Rev. *A
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