Programing/Debugging When The Power Supply Is Not From Stlink-V3E (5V_Stlk); Power Supply Output; Internal Power Supply - ST STM32U5 User Manual

External 3V3 power supply input. In some situations, it is interesting to use an external 3.3 V source on the
3V3 input (CN8 pin 7 or CN11 pin 16), for instance in case the 3.3V is provided by an extension board. When
the Nucleo-144 is powered with only a 3.3V source, the STLINK-V3E part is not powered, thus programming and
debugging are unavailable.
When using the 3V3 input the STLINK-V3E part is not supplied.
For this configuration, it is recommended to remove SB1 to avoid backward voltage to 5 V through U10, and
remove JP2 to avoid STM32 MCU reset from the STLINK-V3E part.
VDD power supply input. In some situations, it is interesting to use an external power source from 1.71 to 3.6 V
to power only the MCU power supply pins (JP4 pin 2 or JP5 pin 2). In this configuration, external functions like
debugging, LED, or the expansion connector are not powered. This option can be used for the optimized MCU
power consumption measurement.
6.4.2

Programing/debugging when the power supply is not from STLINK-V3E (5V_STLK)

In case the current consumption of the Nucleo-144 and the expansion boards exceeds the allowed current on the
ST-LINK USB connector, the external power 5V_VIN, 5V_EXT, or 5V_USB_C can be used. In such a case, it is
still possible to use the embedded ST-LINK for VCP programming and debugging.
In this case, 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 5 V green LED (LD5) is turned ON.
5. Connect the PC to the USB connector (CN1) for programming/debugging.
If this sequence is not respected, the board might be powered by V
risk might be encountered:
• If more than 500 mA current is needed by the board, the PC might be damaged or the current can be
limited by the 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: Whatever the power source (5V_STLK, 5V_VIN, 5V_EXT, 5V_CHGR, or 5V_USB_C) the generated
5 V is present on CN8 pin 9 or CN11 pin 18 and 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
needs to 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 (500 mA including the Nucleo and shield
boards consumption).
6.4.4

Internal power supply

The Nucleo boards are designed to support two specific voltage configurations:
• VDD at 3.3 V configuration to reach Nucleo-144 low-power mode
• VDD at 1.8 V configuration to demonstrate MCU low-voltage capability
6.4.4.1 3V3
Regardless of the 5 V power source, an LDO is used to deliver a fixed 3.3 V power voltage from 5 V. The
maximum current capability of this source is 500 mA. To select the 3.3V voltage for the VDD, set the VDD jumper
(JP4) on [1-2].
A solder bridge (SB1) is used to disconnect the LDO output when an external 3.3 V is applied to the Nucleo-144
board, to avoid backward voltage to 5 V through this LDO.
• SB1 ON: U10 LDO output provides a 3V3 power supply (default configuration).
• SB1 OFF: U10 LDO output does not provide 3V3. An external 3.3 V power source is needed.
UM2861 - Rev 5
Power supply and power selection
first from STLINK-V3E, and the following
BUS
UM2861
®
Table 8
page 22/49