Supplying The Main Board Through The St-Link/V2-1 Usb Port; Using St-Link/2-1 Along With Powering Via The Power Jack - ST STM32L4R9I User Manual

UM2248
to drive the boards with either fixed 3.3 V or with an adjustable voltage regulator controlled by
the RV3 potentiometer and producing a range of voltages from 1.71 to 3.6 V.
6.5.1

Supplying the main board through the ST-LINK/V2-1 USB port

To power STM32L4R9I-EVAL in this way, the USB Host (a PC) gets connected with the
STM32L4R9I-EVAL main board Micro-B USB receptacle, via a USB cable. This event is the
beginning of the USB enumeration procedure. In its initial phase, the host's USB port
current supply capability is limited to 100 mA. It is enough because only the ST-LINK/V2-1
part of STM32L4R9I-EVAL draws power at that time. If the SB33 solder bridge is OFF, the
ST890 power switch (U22) is set in the OFF position, which isolates the remainder of
STM32L4R9I-EVAL from the power source. In the next phase of the enumeration
procedure, the host PC informs the ST-LINK/V2-1 facility of its capability to supply up to 300
mA of current. If the answer is positive, the ST-LINK/V2-1 sets the ST890 switch (U22) to
the ON position to supply power to the remainder of the STM32L4R9I-EVAL main board. If
the PC USB port is not capable of supplying up to 300 mA of current, the power jack (CN18)
is available to supply the main board.
If a short circuit occurs on the main board, the ST890 power switch protects the USB port of
the host PC against a current exceeding 600 mA. In such an event, the LD8 LED lights up.
The STM32L4R9I-EVAL main board can also be supplied by a USB power source not
supporting enumeration, such as a USB charger, as shown in
ST890 power switch ON regardless of the enumeration procedure result and passes the
power unconditionally to the main board.
The LD7 red LED turns on whenever the whole main board is powered.
6.5.2

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

If the main board requires more than 300 mA of supply current, the host PC, connected to
the ST-LINK/2-1 USB port and used for debugging or flashing STM32L4R9AII6, cannot
provide such a current. In such a case, the main board is supplied through CN18 (marked
PSU_DC5V on the main board).
To do this, it is important to power the main board before connecting it with the host PC,
which requires the following sequence to be respected:
1. Set the jumper on the header (JP11) in the E5V position,
2. Connect the external 5 V power source to CN18,
3. Check that the red LED LD7 is turned on,
4. Connect the host PC to the USB connector (CN12).
In case the main board requires more than 300 mA and the host PC is connected via USB
before the main board is powered from CN18, 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 overcurrent protection on its USB port. It is damaged due to the
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
UM2248 Rev 5
Hardware layout and configuration
Table 5. ST-LINK/V2-1 turns the
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