AN4365 datasheet(11/35 Pages) STMICROELECTRONICS

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DocID025303 Rev 2

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AN4365

STM32F4 power consumption

1.2.6

I/O configuration

By default, STM32F4 pins are configured as inputs, except some JTAG pins which can

impact the power consumption of the device in different power modes because pins are very

sensitive to external noise in input mode I/O.

To avoid extra I/O current, all pins should be configured as analog input (AIN); in this mode

the Schmitt trigger input is disabled, providing zero consumption for each I/O pin.

We recommend that the I/O speed frequency (driving level) be configured at the lowest

possible speed or as an output push-pull configuration, outputting 0 to the ODR. The user

should also disable the MCO pin of the clock output if not used.

1.2.7

Using direct memory access (DMA)

STM32F4 devices have peripherals with DMA. This feature is not just useful to improve

performance, it can also be used to reduce power. Peripherals with just one buffer register

require the CPU to remain in operation in order to read from the buffer so it does not

overflow. However, with DMA, the CPU can go to sleep until the DMA transfer completes.

This allows the device to consume less average current over the life of the application.

1.2.8

Power mode switching

Power mode switching in application processing reduces the overall average consumption

by keeping the device as much as possible in low-power modes. Figure 1 illustrates this

power management method.

For example:

Total power = Iaverage * V, with:

Iaverage = (IRun *TimeRun + IStandby * TimeStandby + ISleep * TimeSleep + IStop * TimeStop) / Total time

1.2.9

Code optimization

The user should apply the best optimization techniques to minimize the number of cycles

required for active processing tasks and the active current required.

Using compiler optimization minimizes the time spent executing instructions (speed) and

minimizes branches in code (size), and so minimize the current draw.

Making direct read/write to/from registers instead of using firmware which contains many

loops and instructions avoids an extra current consumption.

To achieve the lowest current consumption, the user can do extra optimizations which can

not be performed by a compiler optimizer. Simplifying the program flow for common cases

will avoid significant processing time and reduce the required memory.

AN4365 Datasheet(PDF) 11 Page - STMicroelectronics