Digilent D2XL - Manual (Page 5)

Digilent D2XL Reference Manual Digilent, Inc.
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Power Supplies
The D2XL board uses two LM317 1.5A voltage regulators to produce 2.5VDC and 3.3VDC supplies.
The regulator inputs are driven from an external DC power supply connected to the on-board 2.1mm
center-positive power jack. The regulators have 10uF of input capacitance, 20uF of local output
capacitance, and 10uF of regulation bypass capacitance. This allows the regulators to produce stable,
low noise supplies using inexpensive power supplies, regardless of load (up to 1.5A). The regulator
bodies are soldered to the board for improved thermal dissipation. DC supplies in the range of 5VDC
to 10VDC may be used.
The D2XL board uses a four layer PCB, with the inner layers dedicated to VCC and GND planes.
Most of the VCC plane is at 3.3V, with an island under the FPGA at 2.5V. The FPGA and the other
ICs on the board all have 0.1uF bypass capacitors placed as close as possible to the VCC pins.
Total board current is dependant on FPGA configuration, clock frequency, and external connections.
In test circuits with roughly 50K gates routed, a 50MHz clock source, and a single expansion board
attached (the DIO2 board), approximately 200mA +/- 30% of supply current is drawn from the 2.5V
supply, and approximately 150mA +/- 50% is drawn from the 3.3V supply. These currents are strongly
dependent on FPGA and peripheral board configurations.
All FPGA VCCO pins are connected to the 3.3V supply. If other VCCO voltages are required, please
contact Digilent for information regarding various options (Digilent can be contacted through
www.digilentinc.com).
Pushbutton and LED
A single pushbutton and LED are provided on the board allowing basic status and control functions to
be implemented without a peripheral board. As examples, the LED can be illuminated from a signal in
the FPGA to verify that configuration has been successful, and the pushbutton can be used to provide
a basic reset function independent of other inputs. The circuits are shown below.
Xilinx
Spartan 2
TQ144
P15
P38
Vdd
4.7K
4.7K
Push
button
80 Ohm
Figure 5. Pushbutton and LED detail