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UM1935
Hardware Layout and configuration
76
required power, the enumeration succeeds, the power transistor U18 (ST890) is switched
ON, the red LED LD10 is turned ON, thus STM32479I-EVAL board is powered and can
consume maximum 300mA current, but not more. If the host is not able to provide the
requested current, the enumeration fails. Therefore the ST890 (U18) remains OFF so
consequently 3.3 V domain of the board and MCU will not be powered. As a consequence
the red LED LD10 remains turned OFF. In this case it is mandatory to use an external power
supply as extra power supply.
E5V (from PSU) or D5V can be used as external power supply in case current consumption
of STM32479I-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, 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 JP14 for PSU or D5V side
2. Check that JP20 is removed
3. Connect the external power source to PSU or D5V (daughterboard mounted)
4. Check red LED LD10 is turned ON
5. Connect the PC to USB connector CN22
If this order is not respected, the board may be powered by V
BUS
first then E5V or D5V, and
the following risks may be encountered:
1. If more than 300mA current is needed by the board, the PC may be damaged or current
can be limited by the PC. As a consequence the board is not powered correctly.
2. 300mA will be requested at enumeration (since JP20 must be OFF), so there is risk that
request is rejected and enumeration does not succeed if PC can’t provide such current.
Consequently the board is not powered (LED LD10 remains OFF).
Note:
In case the board is powered by an USB charger, there is no USB enumeration, so the led
LD10 remains set to OFF permanently and the board is not powered. Only in this specific
case the jumper JP20 needs to be set to ON, to allow the board to be powered anyway.
The power supply is configured by setting the related jumpers
JP2, JP10 and JP14
as
described in
Table 1: Power related jumpers
.
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