Digilent chipKIT Uno32 Referentiehandleiding - Pagina 8
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output short circuit protection and internal
thermal protection and will shut down
automatically to prevent damage.
The 3.3V regulator is a Microchip MCP1725.
This regulator is rated for a maximum output
current of 500mA. The absolute maximum
input voltage for the MCP1725 is 6V. This
regulator has internal short circuit protection
and thermal protection. It will get noticeably
warm when the current consumed by the
VCC3V3 bus is close to the 500mA maximum.
The 5V power bus, VCC5V0 can be powered
from one of three sources:
the USB5V0 bus when the board is
•
operating under USB power,
the output of the on-board 5V regulator
•
when operating from an external 7V-
15V supply,
directly from the external supply when
•
operating from a regulated 5V external
supply with jumper JP2 in the BYP
position.
Switch-over from USB power to external power
is done automatically and the external supply
will be used if both are present.
Jumper JP2 is used to route the external
power supply voltage through the on-board 5V
regulator or directly to the VCC5V0 bus,
bypassing the on-board 5V regulator.
Normally, JP2 is in the REG position. This
routes the external supply through the 5V
regulator. Operation from an externally
regulated 5V supply is provided by placing the
jumper in the BYP position.
The forward drop across the MCP1725 is
typically 210mV (350mV max) at 500mA
output. With JP2 in the BYP position, this will
allow correct operation of the 3.3V power
supply from an input voltage down to 3.5V.
This lets you power the board from batteries
and other lower voltage power sources. In that
case, the VCC5V0 power bus will not be
powered at 5V.
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Note: When JP2 is in the BYP position, do not
apply more than 6V to the external power
input. This can destroy the 3.3V regulator and
possibly the PIC32 microcontroller as well.
The PIC32 microcontroller is rated to use a
maximum of 75mA of current when operating
at 80Mhz. This allows up to 425mA from the
VCC3V3 bus and up to 925mA from the
VCC5V0 bus to power external devices.
The POWER connector, J2, is used to power
shields connected to the Uno32 board. The
following pins are provided on this connector:
P32_RST (pin 1): This connects to the MCLR
pin on the PIC32 microcontroller and can be
used to reset the PIC32.
VCC3V3 (pin 2): This routes the 3.3V power
bus to shields. This pin can provide ~425mA.
VCC5V0 (pin 3): This routes the 5V power
bus to shields. This pin can provide up to
~900mA to shields, however the total
provided by pins 2 and 3 shouldn't exceed
925mA.
GND (pin 4, 5): This provides a common
ground connection between the Uno32 and
the shields.
VIN (pin 6): This connects to the voltage
provided at the external power supply
connector. This can be used to provide
unregulated input power to the shield. It can
also be used to power the Uno32 board from
the shield instead of from the external power
connector.
5V Compatibility
The PIC32 microcontroller operates at 3.3V.
The original Arduino boards operate at 5V as
do many Arduino shields.
There are two issues to consider when dealing
with 5V compatibility for 3.3V logic. The first is
protection of 3.3V inputs from damage caused
by 5V signals. The second is whether the 3.3V
output is high enough to be recognized as a
logic high value by a 5V input.
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