UM1817 datasheet(13/58 Pages) STMICROELECTRONICS

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UM1817

Hardware layout and configuration

If this order is not respected, the board may be powered by VBUS first then E5V or D5V,

and the following risks may be encountered:

If more than 300 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.

300 mA is requested at enumeration (since JP18 must be OFF), so there is risk that the

request is rejected and the enumeration does not succeed if the PC cannot provide

such current. Consequently the board is not powered (LED LD5 remains OFF).

Note:

In case the board is powered by a USB charger, there is no USB enumeration, so the led

LD5 remains set to OFF permanently and the board is not powered. Only in this specific

case the jumper JP18 needs to be set to ON, to allow the board to be powered anyway.

Figure 6 helps to understand the structure of the power source on the evaluation board.

Figure 6. Structure of the power source

The power source is selected by setting the related jumpers JP15, JP7 and JP10 as

described in Table 2.

UM1817 数据表(PDF) 13 Page - STMicroelectronics