External 3V3 power supply input
. In certain situations, it is interesting to use an external 3V3 (CN8 pin 7, CN11
pin 16, or JP5 pin 2) directly as power input, for instance in case the 3V3 is provided by an extension board.
When Nucleo is powered by 3V3, the STLINK-V3E is not powered thus programming and debug features are
unavailable.
With external 3V3 the STLINK-V3E part is not supplied, so JP2 (T_NRST) must be removed to avoid keeping the
target MCU in the reset state.
6.4.2
Programing/debugging when the power supply is not from STLINK-V3E (5V_STLK)
VIN, 5V_EXT, or 5V_USB_C can be used as an external power supply, in case the current consumption of the
Nucleo with expansion boards exceeds the allowed current on USB. In such a condition, it is still possible to use
USB for communication for programming or debugging only.
In this case, it is mandatory to power the board first using VIN, 5V_EXT, or 5V_USB_C then connect the USB
cable to the PC. Proceeding this way the enumeration succeeds, thanks to the external power source.
The following power sequence procedure must be respected:
1.
Connect the JP6 jumper according to the 5V selected external power source.
2.
Connect the external power source according to JP6.
3.
Power ON the external power supply.
4.
Check that the LD5 5V green LED is turned ON.
5.
Connect the PC to the CN1 USB connector.
If this sequence is not respected, the board may be powered by V
BUS
first from STLINK-V3E, and the following
risk may be encountered:
•
If more than 500 mA current is needed by the board, the PC may be damaged or current can be limited by
PC. Therefore, the board is not powered correctly.
•
500 mA is requested at enumeration so there is a risk that the request is rejected and enumeration does
not succeed if PC cannot provide such current. Consequently, the board is not powered (LD5 LED remains
OFF).
6.4.3
Power supply output
•
5V
: When the Nucleo board is powered by USB, VIN, or 5V_EXT, the 5V present on CN8 pin 9 or CN11
pin 18 can be used as an output power supply for an ARDUINO
®
shield or an extension board. In this case,
the maximum current of the power source specified in
must be respected.
•
3V3
: The internal 3V3, on CN8 pin 7 or CN11 pin 16, can be used also as power supply output. The current
is limited by the maximum current capability of the U10 regulator (LD39050PUR33 from STMicroelectronics:
500 mA maximum concerning Nucleo board with shield consumption).
6.4.4
Internal power supply
The Nucleo boards are designed to support two specific voltage configurations:
•
3V3 VDD configuration to reach the Nucleo low-power mode with 3.3 V
•
1V8 VDD configuration to demonstrate the MCU low-voltage capability
6.4.4.1
3V3
Regardless of the 5V power source, an LDO is used to switch from 5V to the 3V3 default power source of the
VDD. The maximum current capability of this source is 500 mA. To select the 3V3 voltage for the VDD, set the
JP4 jumper on [1
‑
2].
A Solder Bridge SB1 is used to disconnect the LDO output when an external 3V3 is applied to the Nucleo board.
•
SB1 ON: U10 LDO output provides a 3V3 power supply (default configuration).
•
SB1 OFF: U10 LDO output does not provide 3V3. An external 3V3 is needed.
6.4.4.2
1V8
An external SMPS can be used for the MCU to work at 1V8. This helps to demonstrate the 1V8 MCU capability.
The external SMPS capability is 400 mA. Before using the 1V8 voltage it is necessary to check that all interfaces
are 1V8 compatible and the maximum current requested does not exceed 400mA. To select the 1V8 voltage for
the VDD, set the JP4 jumper on [2
‑
3].
UM2861
Power supply and power selection
UM2861
-
Rev 2
page 23/49
