Table 8.
SB1 bypass USB Power protection
SB
Default position
Power supply
Limitation
SB1
OFF (not soldered)
USB PWR through
CN1
500 mA limited by Power switch
ON (soldered)
100 mA
OFF (not soldered)
VIN or 5V_EXT PWR
No current limitation
ON (soldered)
Forbidden configuration
1. SB1 must be removed when the board is powered by 5V_EXT (CN11 pin 6) or by VIN (CN8 pin 15 or CN11 pin 24).
Warning:
In case maximum current consumption of the Nucleo and its extension boards exceeds 500 mA, it
is recommended to power the Nucleo using an external power supply connected to 5V_EXT or
VIN.
External 3V3 power supply input
. In certain situations, it is interesting to use the 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 ST-LINK is not powered thus programming and debug features are unavailable.
Two different configurations are possible to use 3V3 to power the board:
•
When ST-LINK is removed (PCB cut)
•
When 3V3 is provided from a shield, on CN8 pin 7, or CN11 pin 16. In this case, it is recommended to
removed SB3 (U6 3V3 regulator output protection) to not inject voltage at the output of U6
With external 3V3 ST-LINK part is not supplied, so JP3 (T_NRST) must be removed.
6.4.2
Programing/debugging when the power supply is not from ST-LINK (5V_STLK)
VIN, 5V_EXT or 5V_USB_TYPE_C can be used as an external power supply, in case the current consumption of
Nucleo and 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_TYPE_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.
Make sure that SB1 is removed.
3.
Connect the external power source according to JP6.
4.
Power ON the external power supply.
5.
Check that 5V GREEN LED LD6 is turned ON.
6.
Connect the PC to the CN1 USB connector.
If this sequence is not respected, the board may be powered by V
BUS
first from ST-LINK, 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 (since SB1 must be OFF) so there is a risk that request is rejected and
enumeration does not succeed if PC cannot provide such current. Consequently, the board is not powered
(LED LD6 remains OFF).
6.4.3
External power supply output
•
5V: When the Nucleo board is powered by USB, VIN or 5V_EXT, this 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
•
3V3: The internal 3V3, on CN8 pin 7 or CN11 pin 16, can be used also as a power supply output. The
current is limited by the maximum current capability of the regulator U6 (LD39050PUR33 from
STMicroelectronics: 500 mA max concerning Nucleo board consu shield consumption).
UM2581
Power supply
UM2581
-
Rev 2
page 21/48