AM_LDO_VCORE0
LPM3.5
All Active Modes
LPM4.5
Changing Core Voltages
434
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Power Control Manager (PCM)
Figure 8-6. Valid LPM3.5 and LPM4.5 Transitions
8.6
Changing Core Voltages
8.6.1 Increasing V
CORE
for Higher MCLK Frequencies
With a reset, V
CORE
and the SVSMH threshold default to their lowest possible levels. These default settings
allow a wide range of MCLK operation, and in many applications, no change to these levels is required.
However, if the application requires the performance provided by higher MCLK frequencies, the V
CORE
level must be increased. See the device-specific data sheet for the specific maximum MCLK frequency at
each V
CORE
level.
See the device-specific data sheet to determine if the new V
CORE
level has a higher minimum V
CC
voltage
requirement and, if so, ensure that it is met. Then software must request the new V
CORE
level voltage and
verify that it is met before changing MCLK, because failing to supply sufficient voltage to the CPU could
produce unpredictable results or result in a POR.
After requesting a power mode with a higher V
CORE
level when the current power mode uses a lower V
CORE
level, there is a delay until the new voltage has been established. Software must not increase the MCLK
frequency until the necessary core voltage has settled.
8.6.2 Decreasing V
CORE
for Power Optimization
The concern posed by increasing MCLK frequency does not exist when decreasing MCLK, because the
V
CORE
level can still support MCLK frequencies below the ones for which they were intended. However,
significant power efficiency gains can be achieved by operating V
CORE
at the lowest value required for a
given MCLK frequency. To decrease V
CORE
level, ensure that the current MCLK frequency is supported at
the new V
CORE
level and then select the new power mode.
8.7
Arm Cortex Processor Sleep Modes
Arm Cortex processors have two instructions that can be used to place the processor in a sleep condition,
namely WFI and WFE. Another mode called sleep-on-exit is also available. These instructions are also
used by the PCM for entry into LPM0, LPM3, and LPM4 modes of operation. The instructions are
described briefly in the following sections. See the Arm documentation for complete details.