6.3
Power supply
6.3.1
Board power supply description
The STM32H7B3I-EVAL Evaluation board is designed to be powered from 5 V DC power source. It incorporates a
precise polymer Zener diode (Poly-Zen) protecting the board from damage due to the wrong power supply. One of
the following six 5 V DC power inputs can be used, upon an appropriate board configuration:
•
5V DC power adapter connected to CN17, the power jack on the board (EXT on the JP29 silkscreen).
This is the default configuration.
•
5V DC power with 500 mA limitation from CN21, the Micro-B USB connector of STLINK-V3E (STLK on the
JP29 silkscreen). As explained below, if the USB enumeration succeeds, the ST-LINK U5V power is
enabled, by asserting the PWR_EN pin. This pin is connected to a power switch U22, which powers the
board. This power switch features also a current limitation to protect the PC in case of short-circuit on board.
If overcurrent (More than 600 mA) happens onboard, the LED LD11 is lit.
•
5V DC power with 500 mA limitation from CN14, the USB OTG HS Micro-AB connector (HS on the HJP29
silkscreen)
•
5V DC power with 500 mA limitation from CN27, the USB OTG FS Micro-AB connector (FS on the JP29
silkscreen)
•
5V DC power from CN5 and CN6, the extension connectors for daughterboard (D on the JP29 silkscreen)
•
5V DC power without limitation from CN21, the Micro-B USB connector of STLINK-V3E (CHGR on the JP29
silkscreen)
The STM32H7B3I-EVAL Evaluation board can be powered from ST-LINK USB connector CN21 (“STLK”), but only
the ST-LINK circuit has the power before USB enumeration, for the host PC only provides 100 mA to the boards
at that time. During the USB enumeration, the STM32H7B3I-EVAL board asks for the 500 mA power to the Host
PC.
•
If the host is able to provide the required power, the enumeration succeeds, the power transistor U22 is
switched ON, the green LED LD7 is turned ON, thus the STM32H7B3I-EVAL board is powered and can
consume a maximum current of 500 mA current, but not more.
•
If the host is not able to provide the requested current, the enumeration fails. Therefore, the power switch
(U22) remains OFF, so consequently, 3.3 V domain of the board and MCU are not powered. As a
consequence, the green LED LD7 remains turned OFF. In this case, it is mandatory to use an external
power supply as an extra power supply.
“EXT” from PSU or “D” can be used as an external power supply in case current consumption of the
STM32H7B3I-EVAL board exceeds the allowed current on USB. In this condition, it is still possible to use USB for
communication for programming or debugging only, but it is mandatory to power the board first using E5V or D5V,
and then connecting the USB cable to the PC. Proceeding this way ensures that the enumeration succeeds
thanks to the external power source.
The following power sequence procedure must be respected:
1.
Connect jumper JP29 to EXT or D side.
2.
Connect the external power source to EXT or D (With mounted daughterboard).
3.
Check green LED LD7 is turned ON.
4.
Connect the PC to USB connector CN21.
If this order is not respected, the board may be powered by VBUS first then “EXT” or “D”, and the following risks
may be encountered:
1.
If more than 500 mA current is needed by the board, the PC may be damaged or current can be limited by
PC. As a consequence, the board is not powered correctly.
2.
500 mA is requested at enumeration, so there is a risk that request is rejected and enumeration does not
succeed if PC cannot provide such current. Consequently, the board is not powered and LED LD7 remains
OFF.
UM2662
Power supply
UM2662
-
Rev 1
page 16/95
