Digilent 410-185P-KIT - Manual (Page 4)

Cerebot MC7 Reference Manual
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board from an external power supply or battery
at up to 24V DC.
There are two power options for main power to
the board: from an external power source via
the on-board 5V switching regulator or USB
powered from the debug USB connector, J13.
To power the board from an external power
supply, place a shorting block on JP14 (labeled
REG).To select USB power from the USB
debug connector, place a shorting block on
JP15 (labeled USB). Note that the dsPIC and
other circuitry on the board, plus connected
Pmods and I
2 C devices can be powered from
the USB connector. External loads such as
motors and hobby servos can not be powered
from the USB connector
NOTE: A shorting block should be installed on
either JP14 or JP15, but never both at the
same time. If shorting blocks are installed on
both at the same time, 5V from the on-board
switching regulator could back-feed to the USB
port, potentially damaging the USB port of the
PC or USB hub.
When powering the board from an external
power supply, there are three power supply
connectors that can be used: J21, J22 and
J24.
Connector J21 is a screw terminal connector
providing an alternative power supply
connection for use with battery packs, bench
supplies or other power sources where use of
a hard wired power supply is desirable.
Connector J22 is a two pin header connector
that can be used with some battery packs or
other wired connections. This connector is
rated for a maximum input current of 2A.
The barrel connector, J24, is used to power the
board from a “wall wart” style power supply.
This type of power supply is available from
many sources. Digilent has an optional power
supply available, the 5V Switching Power
Supply, that can be used with connector J17.
Connector J17 is a 2.5mm x 5.5mm coaxial
connector wired with the center terminal as the
positive voltage.
Connectors J21, J22, and J24 are wired in
parallel and connect directly to the input of the
switching 5V regulator.
NOTE: The dropout of the switching 5V
regulator is approximately 100mV when
operated from a 5V input. This allows
operation of the board from an external 5V
supply.
The dsPIC microcontroller and on-board I/O
devices operate at a supply voltage of 3.3V
provided by the BRD3V3 bus. The regulated
voltage on this bus is provided by a Microchip
MCP1725 Low Dropout voltage regulator,
IC22. This regulator is capable of providing a
maximum of 500mA of current. The DSPIC33
microcontroller will use approximately 90mA
when running at 40 MIPS. The other circuitry
on the board will draw 10-20 mA. The
remaining current is available to provide power
to attached Pmods and I
2 C devices. The
voltage regulator is on the bottom of the board,
below Pmod connector JA, and will get warm
when the amount of current being used is
close to its limit.
The Cerebot MC7 can provide power to any
peripheral modules attached to the Pmod
connectors, JA-JC, and to I
2 C devices powered
from the I 2 C daisy chain connectors, J6 and J8.
Each Pmod connector provides power pins
that can be powered from either the switched
main power bus, BRD5V0, or regulated
voltage, BRD3V3, by setting the voltage
jumper block to the desired position. The I
2 C
power connectors only provide regulated
voltage, BRD3V3.
Half Bridge Circuits
The Cerebot MC7 circuit provides four half
bridges. A half bridge is made up of two
stacked transistors such that the high side
transistor can source current from the motor
power supply and the low side transistor can
sink current to the supply ground.
Each half bridge is made up of an On
Semiconductor NTMD4820N dual N-FET to