Using St-Link/2-1 Along With Powering Via The Power Jack (Cn22); Figure 5. Power Jack (Cn22) Polarity - ST STM32L476ZG User Manual

Hardware layout and configuration
6.3.2

Using ST-LINK/2-1 along with powering via the power jack (CN22)

The board might require more than 300 mA of supply current. It cannot be supplied from the
host PC connected to the ST-LINK/2-1 USB port for debugging or flashing STM32L476ZG.
In such a case, the board can be supplied through CN22 (marked PSU _E5V on the board).
To do this, it is important to power the board before connecting it with the host PC, which
requires the following sequence to be respected:
1. Set the jumper in the JP15 header in the PSU position.
2. Connect the external 5 V power source to CN22.
3. Check that the red LED (LD7) is turned on.
4. Connect the host PC to the USB connector (CN17).
In case the board demands more than 300 mA and the host PC is connected via USB
before the board is powered from CN22, there is a risk of the following events occurring, in
the order of severity:
1. The host PC can supply 300 mA (the enumeration succeeds) but it does not
incorporate any protection on its USB port. It is damaged due to an overcurrent.
2. The host PC can supply 300 mA (the enumeration succeeds) and it has built-in
overcurrent protection on its USB port, limiting or shutting down the power out of its
USB port when the excessive current demand from STM32L476G-EVAL is detected.
This causes an operating failure to STM32L476G-EVAL.
3. The host PC cannot supply 300 mA (the enumeration fails) so
ST-LINK/V2-1 does not supply the remainder of STM32L476G-EVAL from its USB port
VBUS line.
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Figure 5. Power jack (CN22) polarity

UM1855 Rev 6
UM1855