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Power Management Introduction
4.1
Power Management Introduction
Different operating modes, or power modes, are used to allow low-power operation. Ultralow-power
operation is obtained by turning off the power supply to modules to avoid static (leakage) power
consumption and also by using clock gating and turning off oscillators to reduce dynamic power
consumption.
The five various operating modes (power modes) are called active mode, idle mode, PM1, PM2, and PM3
(PM1/PM2/PM3 are also referred to as sleep modes). Active mode is the normal operating mode, whereas
PM3 has the lowest power consumption. The impact of the different power modes on system operation is
shown in
, together with voltage regulator and oscillator options.
Table 4-1. Power Modes
Voltage Regulator
Power Mode
High-Frequency Oscillator
Low-Frequency Oscillator
(Digital)
A
32-MHz XOSC
C
32-kHz XOSC
Configuration
B
16-MHz RCOSC
D
32-kHz RCOSC
Active / idle mode
A or B
C or D
ON
PM1
None
C or D
ON
PM2
None
C or D
OFF
PM3
None
None
OFF
Active mode: The fully functional mode. The voltage regulator to the digital core is on, and either the
16-MHz RC oscillator or the 32-MHz crystal oscillator or both are running. Either the 32-kHz RCOSC or
the 32-kHz XOSC is running.
Idle mode: Identical to active mode, except that the CPU core stops operating (is idle).
PM1: The voltage regulator to the digital part is on. Neither the 32-MHz XOSC nor the 16-MHz RCOSC is
running. Either the 32-kHz RCOSC or the 32-kHz XOSC is running. The system goes to active mode on
reset, an external interrupt, or when the Sleep Timer expires.
PM2: The voltage regulator to the digital core is turned off. Neither the 32-MHz XOSC nor the 16-MHz
RCOSC is running. Either the 32-kHz RCOSC or the 32-kHz XOSC is running. The system goes to active
mode on reset, an external interrupt, or when the Sleep Timer expires.
PM3: The voltage regulator to the digital core is turned off. None of the oscillators is running. The system
goes to active mode on reset or an external interrupt.
The POR is active in PM2/PM3, but the BOD is powered down, which gives a limited voltage supervision.
If the supply voltage is lowered to below 1.4 V during PM2/PM3, at temperatures of 70
°
C or higher, and
then brought back up to good operating voltage before active mode is re-entered, registers and RAM
contents that are saved in PM2/PM3 may become altered. Hence, care should be taken in the design of
the system power supply to ensure that this does not occur. The voltage can be periodically supervised
accurately by entering active mode, as a BOD reset is triggered if the supply voltage is below
approximately 1.7 V.
The CC2533 and CC2541 have functionality to perform automatically a CRC check of the retained
configuration register values in PM2/PM3 to check that the device state was not altered during sleep. The
bits in
SRCRC.CRC_RESULT
indicate whether there were any changes, and by enabling
SRCRC.CRC_RESET_EN
, the device immediately resets itself with a watchdog reset if
SRCRC.CRC_RESULT
is not 00 (= CRC of retained registers passed) after wakeup from PM2/PM3. The
SRCRC
register also contains the
SRCRC.FORCE_RESET
bit that can be used by software to immediately
trigger a watchdog reset to reboot the device.
For CC2533 and CC2541, additional analog reset architecture adds another brownout detector (the
3VBOD) that senses on the unregulated voltage. The purpose of this 3VBOD is to reduce the current
consumption of the device when supplied with voltages well below the operating voltage.
64
Power Management and Clocks
SWRU191C
–
April 2009
–
Revised January 2012
Copyright
©
2009
–
2012, Texas Instruments Incorporated