Hardware layout and configuration UM1956
16/35 UM1956 Rev 4
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), +5 V (5 V) or +3V3 power supply pins on CN4. In case VIN,
+5 V or +3V3 is used to power the STM32 Nucleo-32 board, this power source must comply
with th
e 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.
6.4.1 Power supply input from USB connector
The STM32 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 STM32 Nucleo-32 board requires 300 mA of current to the host
PC. If th
e host is able to provide the required power, the targeted STM32 microcontroller is
powered and the red LED LD2 is turned on, thus the STM32 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
re
quired 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 Section 6.4.2: External power
supply inputs.
SB1 is configured according to the maximum cur
rent 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 plug
ged). In such condition USB enumeration
will always succeed since no more than 100 mA is requested to the host PC. Possible
co
nfigurations of SB1 are summarized in Table 4.
Table 4. SB1 configuration
Solder bridge state Power supply Allowed current
SB1 OFF (default)
USB power through CN1
300 mA max
SB1 ON 100 mA max
SB1 (ON/OFF) VIN, +3V3 or +5 V power For current limitation refer to Ta ble 5
Warning: If the maximum current consumption of the STM32 Nucleo-32
board and its shield board exceed 300
mA, it is mandatory to
power the STM32 Nucleo-32 board, using an external power
supply connected to VIN, +5 V or +3V3.
Note: In case the board is powered by a USB charge
r, 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 to on, to allow the target STM32 to be powered anyway.
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