Power Supply And Power Selection; Power Supply Input From Usb Connector; Table 3. Sb1 Configuration - ST STM32 NUCLEO-F042K6 User Manual

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6.2

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 (7V-12V), +5V (5V) or +3V3 power supply pins on CN4. In case VIN,
+5V or +3V3 is used to power the 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.
In case the power supply is +3V3, the ST-LINK is not powered and cannot be used.
6.2.1

Power supply input from USB connector

The 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, as
host PC only provides 100 mA to the boards at that time. During the USB enumeration, the
Nucleo-32 board requires 300 mA of current to the host PC. If the host is able to provide the
required power, the targeted STM32 microcontroller is powered and the red LED LD2 is
turned ON, thus the Nucleo-32 board and its shield can consume a maximum of 300 mA
current and not more. If the host is not able to provide the required current, the targeted
STM32 microcontroller and the shield board are not power supplied. As a consequence the
red LED LD2 stays turned OFF. In such case it is mandatory to use an external power
supply as explained in the next
SB1 is configured according to the maximum current consumption of the board. SB1 can be
set 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 condition USB enumeration
will always succeed since no more than 100 mA is requested to the host PC. Possible
configurations of SB1 are summarized in
Solder bridge state
SB1 OFF (default)
SB1 ON
SB1 (ON/OFF)
Warning:
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 STM32 is not powered. In this specific
case the SB1 must be set ON, to allow the target STM32 to be powered anyway.
Section 6.2.2: External power supply

Table 3. SB1 configuration

Power supply
USB power through CN1
VIN, +3V3 or +5V power
If the maximum current consumption of the Nucleo-32 board
and its shield board exceed 300 mA, it is mandatory to power
the Nucleo-32 board, using an external power supply
connected to VIN, +5V or +3V3.
DocID028406 Rev 1
Hardware layout and configuration
Table 3.
Allowed current
For current limitation refer to
inputs.
300mA max
100mA max
Table 4
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