6.4
Power supply and power selection
The power supply is provided either by the host PC through the USB cable, or by an external source: VIN (7 V-12
V), 5V or 3V3 power supply pins on CN4. In case VIN, 5V or 3V3 is used to power the STM8 Nucleo-32 board,
this power source must comply with the standard EN-60950-1: 2006+A11/2009, and must be Safety Extra Low
Voltage (SELV) with limited power capability.
The MCU power supply is also selectable: 3V3 or 5V.
6.4.1
Power supply input from the USB connector
The STM8 Nucleo-32 board and shield board can be powered from the ST-LINK USB connector CN1. Note that
only the ST-LINK part is power supplied before the USB enumeration phase, as the host PC only provides 100
mA to the boards at that time. During the USB enumeration, the STM8 Nucleo-32 board requires 300 mA of
current to the host PC. If the host is able to provide the required power, the targeted STM8 microcontroller is
powered and the red LED LD2 is turned on, thus the STM8 Nucleo-32 board and its shield consume a maximum
of 300 mA current and not more. If the host is not able to provide the required current, the targeted STM8
microcontroller and the shield board are not power supplied. As a consequence, the red LED LD2 stays turned
off. In such a case, it is mandatory to use an external power supply as explained in the next
6.4.2 External Power supply inputs
.
SB1 is configured according to the maximum current consumption of the board. SB1 can be set to ON to inform
the host PC that the maximum current consumption does not exceed 100 mA (even when ARDUINO
®
Nano
shield is plugged). In such a condition, USB enumeration always succeeds since no more than 100 mA is
requested to the host PC. Possible configurations of SB1 are summarized in
Table 4.
SB1 configuration
Power supply
Maximum current
SB1 OFF
USB power through CN1
300 mA
SB1 ON
100 mA
1. The default configuration is reported in bold style.
Caution:
If the maximum current consumption of the STM8 Nucleo-32 board and its shield board exceeds 300 mA, it is
mandatory to power the STM8 Nucleo-32 board, using an external power supply connected to VIN, 5V or 3V3.
Note:
In case the board is powered by a USB charger, there is no USB enumeration, so the LED LD2 remains set to
off permanently and the target STM8 is not powered. In this specific case, the SB1 must be set to ON, to allow
the target STM8 to be powered anyway.
UM2391
Power supply and power selection
UM2391
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Rev 1
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