UM1956 Rev 4
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UM1956
Hardware layout and configuration
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6.4.2
External power supply inputs
The STM32 Nucleo-32 board and its shield boards can be powered in three different ways
from an external power supply, depending on the voltage used. The three power sources
are summarized in the
Table 5
.
Table 5. External power sources
Input power
name
Connector
pin
Voltage
range
Max current
Limitation
VIN
CN4 pin 1
7 V to 12 V
800 mA
From 7 V to 12 V only and input
current capability is linked to input
voltage:
800 mA input current when VIN=7 V
450 mA input current when
7 V< VIN <9 V
300 mA input current when
10 V> VIN >9 V
less than 300 mA input current when
VIN>10 V
+5 V
CN4 pin 4
4.75 V to
5.25 V
500 mA
ST-LINK not powered
+3V3
CN4 pin 14
3 V to 3.6 V
-
ST-LINK not powered and SB14 and
SB9 must be off.
VIN or +5 V power supply
When powered from VIN or +5 V, it is still possible to use ST-LINK for communication for
programming or debugging only, but it is mandatory to power the board first, using VIN or
+5 V, then to connect the USB cable to the PC. By this way the enumeration will succeed
anyway, thanks to the external power source.
The following power sequence procedure must be respected:
1. Check that SB1 is off
2. Connect the external power source to VIN or +5 V
3. Power on the external power supply 7 V< VIN < 12 V to VIN, or 5 V for +5 V
4. Check red LED LD2 is turned on
5. Connect the PC to USB connector CN1
If this order is not respected, the board may be powered by VBUS first, then by VIN or +5 V,
and the following risks may be encountered:
1.
If more than 300 mA current is needed by the board, the PC may be damaged or
current supplied is limited by the PC. As a consequence the board is not powered
correctly.
2. 300 mA is requested at enumeration (since SB1 must be off) so there is the risk that
the request is rejected and the enumeration does not succeed if the the PC cannot
provide such current. Consequently the board is not power supplied (LED LD2 remains
off).
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