ST STM32L4+ Series Reference Manual page 190

Power control (PWR)
In Range1, the main regulator operates in two modes following the R1MODE bit in the
PWR_CR5 register:
•
Main regulator Range 1 normal mode: provides a typical output voltage at 1.2 V. It is
used when the system clock frequency is up to 80 MHz. The Flash access time for read
access is minimum, write and erase operations are possible.
•
Main regulator Range 1 boost mode: provides a typical output voltage at 1.28 V. It is
used when the system clock frequency is up to 120 MHz. The Flash access time for
read access is minimum, write and erase operations are possible. To optimize the
power consumption it is recommended to select the range1 boost mode when the
system clock frequency is greater than 80 MHz. See
System frequency
R1MODE bit configuration
• Range 2: Low-power range.
The main regulator provides a typical output voltage at 1.0 V. The system clock frequency
can be up to 26 MHz.The Flash access time for a read access is increased as compared to
Range 1; write and erase operations are not possible.
Voltage scaling is selected through the VOS bit in the PWR_CR1 register.
The sequence to go from Range 1 (Normal/Boost) to Range 2 is:
1. In case of switching from Range 1 boost mode to Range 2, the system clock must
2. Reduce the system frequency to a value lower than 26 MHz
3. Adjust number of wait states according new frequency target in Range 2
(LATENCY bits in the FLASH_ACR).
4. Program the VOS bits to "10" in the PWR_CR1 register.
The sequence to go from Range 2 to Range 1 (normal/boost mode) is:
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Table 24. Range 1 boost mode configuration
26 MHz < SYSCLK ≤ 80 MHz
be divided by 2 using the AHB prescaler before switching to a lower system
frequency for at least 1us and then reconfigure the AHB prescaler.:
1
RM0432 Rev 6
Table 24.
80 MHz < SYSCLK ≤ 120 MHz
0
RM0432