Digilent MX7cK - Manual (Page 6)

Cerebot MX7cK Reference Manual
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main power supply will be turned on
immediately when the power switch is turned
on. When load switch IC9 is turned on, it
powers the board unregulated power bus
VCC5V0, which provides the input power to
the main regulator.
The main board power supply is a switch mode
voltage regulator implemented using a
Microchip MCP16301 switch mode step-down
regulator, IC10. This regulator provides 3.3V at
up to 600 mA with approximately 96%
efficiency. When the main power supply is
enabled, it powers the regulated power bus
VCC3V3
When powering the board from an external
power supply, there are two connectors that
can be used: J17 and J18.
The barrel connector, J17, 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 a 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.
Connector J18 is a screw terminal connector
for 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.
Connectors J17 and J18 are wired in parallel
and connect to the EXT position on the Power
Select jumper block J3. A shorting block
should be placed on the “EXT” position of J3
when using this option for board power. Only
one of the external power connectors should
be used at a time. If multiple power supplies
are connected simultaneously, damage to the
board or the power supplies may occur.
When the Cerebot MX7cK is operating as a
USB host, an external power supply connected
to either J17 or J18 must be used to power the
board. In addition to powering the logic on the
Cerebot MX7cK board, this supply provides the USB bus voltage supplied to any connected
USB device and must be a regulated 5V with
at least 500mA current capability to meet the
USB specifications.
The CAN bus operates at 5V, and therefore
the transceivers for the two CAN interfaces
require 5V to operate correctly and within the
CAN specification. When using the CAN
network interfaces, the board should be
operated from a 5V supply if using an external
power supply.
The PIC32 microcontroller and on-board I/O
devices operate at a supply voltage of 3.3V
provided by the VCC3V3 bus. The main
voltage regulator is capable of providing a
maximum of 600mA of current. The PIC32
microcontroller will use approximately 85mA
when running at 80MHz. The SMSC LAN8720
Ethernet PHY consumes approximately 45mA
when operating at 100Mbps. The Microchip
MCP2551 CAN transceivers can draw up to
75mA each when operating the CAN busses.
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 Cerebot MX7cK can provide power to any
peripheral modules attached to the Pmod
connectors, JA-JF, and to I
2
C devices powered
from the I
2
C daisy chain connectors, J7 and J8.
Each Pmod connector provides power pins
that can be powered from either the switched
main power bus, VCC5V0, or regulated
voltage, VCC3V3, by setting the voltage
jumper block to the desired position. The I
2 C
connectors only provide the regulated voltage,
VCC3V3.
Pmod™ Connectors
The Cerebot MX7cK has six connectors for
connecting Digilent Pmod peripheral modules.
The Pmod connectors, labeled JA
–JF, are 2x6
pin, right-angle, female pin header connectors.
Each connector has an associated power
select jumper block labeled JPA
–JPF.