Power Supply Input From The Usb Connector; External Power Supply Inputs: 5V_In - ST STM32F334C8 User Manual

UM1735
5.2.1

Power supply input from the USB connector

ST-LINK/V2-1 supports USB power management allowing to request more than 100 mA
current to the host PC.
All parts of the STM32F334 Discovery board and extension board can be powered from the
ST-LINK/V2-1 USB connector CN1 (U5V or VBUS). 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 STM32F334 Discovery board requires
500 mA of current to the host PC. If the host can provide the required power, the targeted
STM32 microcontroller is powered. The red LED (LD1) is turned on. Thus, the STM32F334
Discovery board and its extension board can consume a maximum of 500 mA current, not
more. If the host is not able to provide the required current, the targeted STM32
microcontroller and the MCU part including the extension board are not power supplied. As
a consequence, the red LED (LD1) remains turned OFF. In such a case, it is mandatory to
use an external power supply as explained in the next chapter.
Warning: If the maximum current consumption of the STM32F334 Discovery and its
extension boards exceeds 500 mA, it is mandatory to power the STM32F334 Discovery
using an external power supply connected to 5V_IN.
Note: In case this board is powered by a USB charger or USB battery, there is no USB
enumeration. Therefore, the red LED (LD1) remains OFF permanently and the target MCU
is not powered. In this specific case, the jumper JP1 needs to be ON to allow the target
MCU to be powered anyway. This is a special use without enumeration and JP1 is OFF. To
use this optional power supply, solder a 2-pin header in JP1 and set a jumper (you can use
a jumper plugged into P3 or P4)
5.2.2

External power supply inputs: 5V_IN

The external power source 5V_IN is automatically detected. In this case, the current
consumption of the STM32F334 Discovery board with its extension board exceeds the
allowed current on USB. In this condition, it is still possible to use the USB for
communication (programming or debugging only), but it is mandatory to power supply the
board first using 5V_IN and then connect the USB cable to the PC. Proceeding this way
ensures that the enumeration occurs thanks to the external power source.
The following power sequence procedure must be respected:
1. Connect the external power source to 5V_IN.
2. Power on the external power supply 5V_IN.
3. Check that LD1 is turned on.
4. Connect the PC to the USB connector (CN1).
If this order is not respected, the board might be supplied by VBUS first, then by 5V_IN, and
the following risks might be encountered:
1. If the board needs a current higher than 500 mA, the PC might be damaged or the PC
can limit the current supply. As a consequence, the board is not powered correctly.
2. Enumeration requires 500 mA (since JP1 must be OFF) so there is a risk that the
request is rejected and the enumeration does not succeed if the PC cannot provide
such current. Consequently, the board is not power supplied, and the red LED (LD1)
remains OFF.
UM1735 Rev 3
Hardware layout
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