STM32F427AI datasheet(112/240 Pages) STMICROELECTRONICS

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Electrical characteristics

STM32F427xx STM32F429xx

112/240

DS9405 Rev 12

I/O system current consumption

The current consumption of the I/O system has two components: static and dynamic.

I/O static current consumption

All the I/Os used as inputs with pull resistors generate current consumption when the pin is

externally held to the opposite level. The value of this current consumption can be simply

computed by using the pull-up/pull-down resistor values given in Table 57: I/O static

characteristics.

For the output pins, any internal or external pull-up or pull-down and external load must also

be considered to estimate the current consumption.

Additional I/O current consumption is due to I/Os configured as inputs if an intermediate

voltage level is externally applied. This current consumption is caused by the input Schmitt

trigger circuits used to discriminate the input value. Unless this specific configuration is

required by the application, this supply current consumption can be avoided by configuring

these I/Os in analog mode. This is notably the case of ADC input pins, which should be

configured as analog inputs.

Caution:

Any floating input pin can also settle to an intermediate voltage level or switch inadvertently,

as a result of external electromagnetic noise. To avoid current consumption related to

floating pins, they must either be configured in analog mode, or forced internally to a definite

digital value. This can be done either by using pull-up/down resistors or by configuring the

pins in output mode.

I/O dynamic current consumption

In addition to the internal peripheral current consumption (see Table 35: Peripheral current

consumption), the I/Os used by an application also contribute to the current consumption.

When an I/O pin switches, it uses the current from the MCU supply voltage to supply the I/O

pin circuitry and to charge/discharge the capacitive load internal or external connected to

the pin:

where

ISW is the current sunk by a switching I/O to charge/discharge the capacitive load

VDD is the MCU supply voltage

fSW is the I/O switching frequency

C is the total capacitance seen by the I/O pin: C = CINT+ CEXT

The test pin is configured in push-pull output mode and is toggled by software at a fixed

frequency.

ISW

VDD fSW C

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