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UM1855
Hardware layout and configuration
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2.3 Power
supply
STM32L476G-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 wrong power supply. One of the following four 5V DC power inputs can be
used, upon an appropriate board configuration:
•
Power jack CN22, marked PSU_E5V on the board. A jumper must be placed in PSU
location of JP17. The positive pole is on the center pin as illustrated in
Figure 5
.
•
Standard-B USB receptacle CN17 of ST-LINK/V2-1, offering enumeration feature
described in
Section 2.3.1
.
•
Micro-AB USB receptacle CN1 of USB OTG interface, marked OTG_FS on the board.
Up to 500mA can be supplied to the board in this way.
•
Pin 28 of CN6 extension connector for custom daughterboards, marked D5V on the
board.
No external power supply is provided with the board.
LD7 red LED turns on when the voltage on the power line marked as +5V is present. All
supply lines required for the operation of the components on STM32L476G-EVAL are
derived from that +5V line.
Table 2
describes the settings of all jumpers related with powering STM32L476G-EVAL and
extension board. VDD_MCU is STM32L476ZGT6 digital supply voltage line. It can be
connected to either fixed 3.3 V or to an adjustable voltage regulator controlled with RV1
potentiometer and producing a range of voltages between 1.71 V and 3.6 V.
2.3.1
Supplying the board through ST-LINK/V2-1 USB port
To power STM32L476G-EVAL in this way, the USB host (a PC) gets connected with the
STM32L476G-EVAL board’s Standard-B USB receptacle, via a USB cable. This event starts
the USB enumeration procedure. In its initial phase, the host’s USB port current supply
capability is limited to 100 mA. It is enough because only ST-LINK/V2-1 part of
STM32L476G-EVAL draws power at that time. If the jumper header JP18 is open, the U37
ST890 power switch is set to OFF position, which isolates the remainder of
STM32L476G-EVAL from the power source. In the next phase of the enumeration
procedure, the host PC informs the ST-LINK/V2-1 facility of its capability to supply up to
300 mA of current. If the answer is positive, the ST-LINK/V2-1 sets the U37 ST890 switch to
ON position to supply power to the remainder of the STM32L476G-EVAL board. If the PC
USB port is not capable of supplying up to 300 mA of current, the CN22 power jack can be
used to supply the board.
The ST890 power switch protects the host’s USB port against current demand exceeding
600 mA, should a short-circuit occur on the board. In such an event, the LD9 LED lights on.
The STM32L476G-EVAL board can also be supplied from a USB power source not
supporting enumeration, such as a USB charger. In this particular case, the JP18 header
must be fitted with a jumper as shown in
Table 2
. ST-LINK/V2-1 turns the ST890 power
switch ON regardless of enumeration procedure result and passes the power
unconditionally to the board.
The LD7 red LED turns on whenever the whole board is powered.
