STM32F302xx/STM32F303xx
Electrical characteristics
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-up generate current consumption when the pin is
externally held low. The value of this current consumption can be simply computed by using
the pull-up/pull-down resistors values given in Table 52: I/O static characteristics.
For the output pins, any external pull-down or 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 (seeTable 36: 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:
ISW = VDD × fSW × C
where
I
is the current sunk by a switching I/O to charge/discharge the capacitive load
is the MCU supply voltage
SW
V
DD
f
is the I/O switching frequency
SW
C is the total capacitance seen by the I/O pin: C = C + C
+C
S
INT
EXT
The test pin is configured in push-pull output mode and is toggled by software at a fixed
frequency.
Doc ID 023353 Rev 5
69/133
STMICROELECTRONICS [ ST ]
