Hardware layout
UM1775
18/39
UM1775 Rev 4
The D3, D4 and D6 diodes protect the 5 V pins from external power supplies:
•
5 V and 3 V can be used as output power supplies when an extension board is
connected to pins P2 and P3.
In this case, the 5V_O and 3V_O pins deliver a 5 V or 3.3 V power supply and the
power consumption of the extension board must be lower than 100 mA.
•
5 V can also be used as input power supply, for instance when the USB connector is
not connected to the PC (pin 5V_I of header P3).
In this case, the STM32L053 Discovery board must be powered by a power supply unit
or by an auxiliary equipment complying with standard EN-60950-1: 2006+A11/2009. It
must be Safety Extra Low Voltage (SELV) with limited power capability.
6.2.1
Power supply input from the USB connector
ST-LINK/V2-1 supports USB power management allowing the request of more than 100 mA
from the host PC.
All parts of the STM32L053 Discovery board and extension board can be powered from the
ST-LINK/V2-1 USB connector CN2 (U5V or V
BUS
). Note that only the ST-LINK/V2-1 part is
power supplied before the USB enumeration as the host PC only provides 100 mA to the
board at that time. During the USB enumeration, the STM32L053 Discovery board requires
300 mA from the host PC.
•
If the host is able to provide the required power, the target STM32 microcontroller is
powered and the red LED LD2 is turned ON. The STM32L053 Discovery board and its
extension board can consume not more than a maximum of 300 mA.
•
If the host is not able to provide the required current, the target STM32 microcontroller
and the MCU part including the extension board are not power supplied. As a
consequence the red LED LD2 remains turned OFF. In such a case, it is mandatory to
use an external power supply as explained in the next section.
Warning: If the maximum current consumption of the STM32L053 Discovery board and its
extension board exceeds 300 mA, it is mandatory to power the STM32L053 Discovery
board with an external power supply connected to 5V_IN.
Note:
In cases where this board is powered by a USB charger or USB battery, there is no USB
enumeration. Therefore, LED LD1 remains OFF permanently and the target MCU is not
powered. In this specific case, the jumper JP2 must be ON to allow the target MCU to be
powered anyway. This is a special use case without enumeration and JP2 is not soldered.
To use this optional power supply, solder a 2-pin header in JP2 and set a jumper.
