Digilent MX4cK - Manual (Page 6)

Cerebot MX4cK Reference Manual
www.digilentinc.com page 6 of 35
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Board Hardware Description
The following describes the various hardware
features of the Cerebot MX4cK board and the
PIC32XM460F512L microcontroller.
Power Supply
Switch SW1, in the lower left corner of the
board is the power switch. Place this switch in
the ON position to turn on board power and in
the OFF position to turn off board power.
The Cerebot MX4cK may be USB powered via
either the USB debug port, the USB UART
port, or the USB device port. Alternatively, the
board may be powered via dedicated,
“external”, power supply connectors.
Jumper block J12 is used to select the power
source used to provide power to the board.
This jumper block provides the following four
positions:
• USB – power is supplied by USB device
connector J15. This is used when the
Cerebot MX4cK is used to implement a
USB bus powered device.
• EXT – Power is supplied by one of the
external power connectors.
• DBG – Power is supplied by DEBUG USB
connector J9.
• URT – Power is supplied by UART USB
connector J8.
Place the shorting block in the appropriate
position on J12 for the desired power source
for the board.
The Cerebot MX4cK is rated for external power
from 3.6 to 12 volts DC. Using a voltage
outside this range could damage the board and
connected devices. If operating the board at a
voltage higher than 5V, it is necessary to
remove the shorting block on jumper JP10 to
protect the USB load switch, which is limited to
a maximum voltage of 5.5V. When operating
from any of the three USB sources, the input
voltage will be 5V.
The output of power select jumper block J12 is
connected to the VIN power bus. The VIN
power bus supplies power to Q3, a PFET load
switch, and IC9, the voltage regulator for the
licensed debugger circuit. The licensed
debugger circuit is powered as soon as the
power switch is turned on. Power to the rest of
the board is controlled by Q3. The main board
power supply is enabled by bringing the gate of
Q3 low. When Q3 is turned on, the unregulated
power bus BRD_VU is powered.
If the licensed debugger is connected to an
active USB port, it enumerates with the host
computer and once it has successfully been
enumerated, it turns on the main board power
supply by driving the PWR_ON signal high.
If the licensed debugger is not connected to an
active USB port, the PWR_ON signal is
ignored and board power is turned on
immediately by the power switch via transistor
Q4.
The main board power supply is a switch mode
voltage regulator implemented using a
Microchip MCP16301 switch mode step-down
regulator. This regulator provides 3.3V at up to
600 mA with approximately 96% efficiency.
This powers the main board regulated power
bus BRD_3V3
There are three connectors on Cerebot MX4cK
for connecting an external power supply: J13,
J14, and J18.
The barrel connector, J13, is useful for desktop
development and testing where using USB or
battery power is not suitable. J13 is the
connector used by the AC adapter optionally
available from Digilent, or other sources. J13
is a 2.5mm x 5.5mm coaxial connector wired
with the center terminal as the positive voltage.