UM2153 datasheet(19/57 Pages) STMICROELECTRONICS

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UM2153

Hardware layout and configuration

7.5

Programming/debugging when the power supply is not from

ST-LINK (5V_ST_LINK)

It is mandatory to power the board first using CN2 (VIN) or CN9 (USB_FS_OTG), 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:

•

Connect the jumper JP4 on (5V_ARD) or (5V_USB_FS)

•

Connect the external power source to CN2 in case of an Arduino shield or to CN9 in

case of USB FS host interface

•

Check that the red LED LD5 is turned ON

•

Connect the PC to USB connector CN7

If this sequence is not respected, the board may be powered by VBUS first from ST-LINK, and

the following risks may be encountered:

•

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.

•

500 mA is requested at the enumeration, so there is a risk that the request is rejected

and enumeration does not succeed if the PC cannot provide such current.

7.6

Clock sources

Three clock sources are described below:

•

X1 which is the 8 MHz oscillator for STM32L475VG microcontroller. This clock is not

implemented in a basis configuration.

•

X2 which is the 32.768 KHz crystal for the STM32L475VG embedded RTC

•

X3 which is the 8 MHz clock from ST-LINK MCU for the STM32L475VG microcontroller.

7.7

Reset sources

The reset signal of the STM32L4 Discovery kit is active low and the reset sources includes:

•

A reset button B1

•

An Arduino Uno V3 shield board from CN2

•

An embedded ST-LINK/V2-1

7.8

USB OTG FS

The STM32L4 Discovery kit supports USB OTG FS communication via a USB Micro-AB

connector (CN9).

To do this the following components must be added by the users:

•

8 MHz crystal (at X1 position); ref: NX3225GD-8.00M

•

8.2 pF capacitor (0402 size) at C2 position

•

8.2 pF capacitor (0402 size) at C4 position

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