
Power control (PWR)
RM0351
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DocID024597 Rev 5
Proper software management through GPIOs to enable/disable SMPS and
connect/disconnect SMPS through the switch, is required to conform with the rules
described below.
Section 5.1.8: Dynamic voltage scaling management
)
It is mandatory to respect the following rules to avoid any damage or instability on either
digital parts or internal regulators:
•
In Run, Sleep and Stop 0 modes, VDD12 can be connected and should respect
–
VDD12 < 1.32 V
–
VDD12
≥
V
CORE
+ 50mV giving for Main Regulator
Range 1, V
CORE
=1.2 V so VDD12 should be greater than 1.25 V
Range 2, V
CORE
=1.0 V so VDD12 should be greater than 1.05 V
–
VDD12
≥
1.08 V in Range 2 when SYSCLK frequency
≥
26 MHz
•
In all other modes, ie LPRun, LPSleep, Stop 1, Stop 2, Standby and Shutdown modes,
VDD12 must be disconnected from SMPS output, ie pin must be connected to an high
impedance output:
–
VDD12 connected to HiZ (voltage is provided by internal regulators)
•
Transitions of VDD12 from connected to disconnected is only allowed when SYSCLK
frequency
≤
26 MHz to avoid to big voltage drop on main regulator side.
Note:
In case of asynchronous reset while having the VDD12
≤
1.25 V, VDD12 should switch to
HiZ in less than regulator switching time from Range 2 to Range 1 (~1 us).
5.1.8 Dynamic
voltage scaling management
The dynamic voltage scaling is a power management technique which consists in
increasing or decreasing the voltage used for the digital peripherals (V
CORE
), according to
the application performance and power consumption needs.
Dynamic voltage scaling to increase V
CORE
is known as overvolting. It allows to improve the
device performance.
Dynamic voltage scaling to decrease V
CORE
is known as undervolting. It is performed to
save power, particularly in laptop and other mobile devices where the energy comes from a
battery and is thus limited.
The main regulator have two possible programmable voltage range detailed below:
•
Range 1: High-performance range.
The main regulator provides a typical output voltage at 1.2 V. The system clock frequency
can be up to 80 MHz. The Flash access time for read access is minimum, write and erase
operations are possible.
•
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 possible.
Voltage scaling is selected through the VOS bit in the PWR_CR1 register.