UM1871 datasheet(13/64 Pages) STMICROELECTRONICS

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UM1871

Hardware layout and configuration

STM32446E-EVAL evaluation board can be powered from ST-LINK USB connector CN16

(U5V), but only ST-LINK part is powered before USB enumeration, because host PC only

provides 100 mA to the boards at that time. During the USB enumeration,

STM32446E-EVAL board asks for the 300 mA power to the Host PC. If the host is able to

provide the required power, the enumeration finishes by a “SetConfiguration” command and

then, the power transistor U11 (ST890) is switched ON, the red LED LD8 is turned ON, thus

STM32446E-EVAL board can consume maximum 300 mA current, but not more. If the host

is not able to provide such requested current, the enumeration fails, therefore the ST890

(U11) remains OFF and the 3.3 V part of the board will not be powered. As consequence,

the red LED LD8 remains turned OFF. In such 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 STM32446E-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 connect the USB cable to the

PC. Proceeding in this way, ensures that the enumeration succeeds thanks to the external

power source.

The following power sequence procedure must be respected:

Connect jumper JP21 for PSU or D5V side

Check that JP18 is removed (PWR_EXT)

Connect the external power source to CN20 (PSU) or D5V (daughterboard mounted)

Check red LED LD8 is turned ON

Connect the PC to USB connector CN16

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 will be requested at enumeration (since JP18 must be OFF), so there is risk

that request is rejected and enumeration does not succeed, if PC cannot provide such

current. Consequently the board is not powered (LED LD8 remains OFF).

Note:1

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

LD8 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.

Note:2

When the board is powered by ST-LINK, the current is limited by U11 and the LED LD11 is

turned ON in case of over current detection.

2.3

Clock source

Two clock sources are available on STM32446E-EVAL evaluation board for

STM32F446ZET6 and RTC embedded (see Table 2: 32 KHz crystal Y2 related solder

bridges and Table 3: 8 MHz crystal Y4 related solder bridges):

•

Y2, 32KHz crystal for embedded RTC

•

Y4, 8MHz crystal with socket for STM32F446ZET6 Microcontroller, Y3, 24MHz crystal

for USB OTG HS

•

Y5, 8MHz crystal for ST-LINK

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