External Power Supply Inputs; Vin Or +5V Power Supply; Table 4. External Power Sources - ST STM32 NUCLEO-F042K6 User Manual

Hardware layout and configuration
6.2.2

External power supply inputs

The Nucleo-32 board and its shields boards can be powered in three different ways from an
external power supply, depending on the voltage used. The three power sources are
summarized in the
Input power
name
VIN
+5V
+3V3

VIN or +5V power supply

When powered from VIN or +5V, it is still possible to use ST-LINK for communication for
programming or debugging only, but it is mandatory to power the board first, using VIN or
+5V, then to connect the USB cable to the PC. By this way the enumeration will succeed
anyway, thanks to the external power source.
The following power sequence procedure must be respected:
1. Check that SB1 is OFF
2. Connect the external power source to VIN or +5V
3. Power on the external power supply 7V< VIN < 12V to VIN, or 5V for +5V
4. Check red LED LD2 is turned ON
5. Connect the PC to USB connector CN1
If this order is not respected, the board may be powered by VBUS first, then by VIN or +5V,
as the following risks may be encountered:
1. If more than 300 mA current is needed by the board, the PC may be damaged or
current supply can be limited by PC. As a consequence the board is not powered
correctly.
2. 300 mA is requested at enumeration (since SB1 must be OFF) so there is risk that
request is rejected and enumeration does not succeed if the PC cannot provide such
current. Consequently the board is not power supplied (LED LD2 remains OFF).
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Table 4.

Table 4. External power sources

Connector Voltage
pin range
CN4 pin 1 7V to 12V
4.75V to
CN4 pin 4
5.25V
CN4 pin 14 3V to 3.6V
DocID028406 Rev 1
Max current
From 7V to 12V only and input
current capability is linked to input
voltage:
800mA input current when VIN=7V
450mA input current when
800mA
7V<VIN<9V
300mA input current when
10V>VIN>9V
less than 300mA input current when
VIN>10V
500mA ST-LINK not powered
ST-LINK not powered and SB14 and
-
SB9 must be OFF.
UM1956
Limitation