Entering LPM0 Modes
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SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Power Control Manager (PCM)
Any time the DCDC_ERROR_IFG flag is set, the PSS automatically switches to LDO as a backup
regulator. The PSS also keeps trying to switch back to DC/DC operation by continuously monitoring the
supply voltage. When the supply voltage is sufficient for DC/DC regulator, the PSS switches back to
DC/DC mode of operation.
DCDC_ERROR_IFG is a sticky bit and is active until the error on DC/DC has been resolved. The
application must ensure minimum supply for DC/DC regulator before it tries to switch to the DC/DC mode
of operation. See the device-specific data sheet for the minimum supply required for the DC/DC to be
operational in the device.
The DCDC_ERROR_IFG flag is triggered under the following scenarios:
1. DCDC_ERROR_IFG during an AM_LDO_VCOREx to AM_DCDC_VCOREx transition due to
inadequate supply for DC/DC operation. In this case, the operating mode remains unchanged at
AM_LDO_VCOREx.
2. DCDC_ERROR_IFG during steady state AM_DCDC_VCOREx operation due to insufficient supply for
DC/DC operation. In this scenario, the application is notified about the DC/DC to LDO fail-safe
operation. The application may then choose to change the power mode permanently back to LDO if
the supply conditions for DC/DC cannot be met.
8.14 Entering LPM0 Modes
The processor System Control register (SCR) is used to enter LPM0 mode. LPM0 mode entry is different
from active mode requests, because the writing of the SCR register does not cause an immediate LPM0
mode entry. Only a WFI, WFE, or SLEEPONEXIT starts the low-power mode entry process. Using the
SCR register can be considered as a way to precondition the device in preparation for LPM0 mode. For
the majority of applications, the setting of these registers is rather infrequent and in some cases, only a
one-time setup is necessary. The basic procedure is as follows:
1. The application selects sleep mode by writing SLEEPDEEP = 0 in the SCR.
2. The LPM0 mode waits for a WFE, WFI, or sleep-on-exit event.
8.15 Exiting LPM0 Modes
The following events wake up the device from LPM0 modes:
•
External reset or NMI (RSTn/NMI)
•
Enabled interrupt and latch events including general-purpose I/O events (see
for details on
wake-up criteria)
•
Debugger events (for example, halt or reset)
8.16 Entering LPM3 or LPM4 Modes
Entering LPM3 or LPM4 mode requires use of the processor System Control Register (SCR). LPM3 or
LPM4 mode entry is different from active mode requests, because the writing of the SCR register does not
cause an immediate LPM3 or LPM4 mode entry. Only a WFI, WFE, or SLEEPONEXIT initiates the low-
power mode entry process to begin. Using the SCR register can be considered as a way to precondition
the device in preparation for LPM3 or LPM4 modes. For the majority of applications, the setting of these
registers is rather infrequent and in some cases, only one time setup is necessary.
The basic steps follow. The first three steps are required to prepare the device for LPM3 or LPM4 entry.
1. The application selects LPM3 or LPM4 mode by writing SLEEPDEEP = 1 in the SCR register and
LPMR = 0h in the PCMCTL0 register.
2. At this time, LPM3 or LPM4 waits for a WFE, WFI, or sleep-on-exit event.
3. On a WFI event, the PCM then checks whether this transition from the current active mode to LPM3 or
LPM4 is valid. See
for the details on the valid LPM3 or LPM4 transitions. If this is not a valid
transition, then PCM sets the LPM_INVALID_TR_IFG flag and then aborts the LPM3 or LPM4 entry
sequence. If, the LPM_INVALID_TR_IFG = 1, and LPM_INVALID_TR_IE = 0, the system enters a
LPM0 mode corresponding to the active mode, till an interrupt event wakes it up.
4. If this is a valid transition, PCM locks the PCMCTL0 and CS registers. In addition, it disables any new