Digilent 6021-210-000P-KIT - Manual (Page 5)

Universal Development Board™ Reference Manual
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Page 5 of 27
1 Power Supply
The UDB can be powered in one of two ways, either by a bench supply or a wall wart type power supply attached
to the power header, J20; or from the USB connector, J23, associated with the USB serial convertor. The UDB is
intended to be operated from a regulated 5V power source, however with certain restrictions, a different supply
voltage can be used. The absolute maximum voltage that should be applied to the power header is 6V.
If an external power source other than a regulated 5V supply is used, the voltage on the VCC5V0 bus will be the
voltage of the external supply, and the test points on the board labeled 5V will actually be at the voltage of the
external supply.
1.1 USB Power
To power the board with from the USB use a USB 2.0 A to Mini B cable to connect the PC to the UDB via connector
J23. The Jumper at J21 (power select) must be placed in the USB position and the power switch, SW1, must be in
the ON position. When the board is powered, the LED at LD8 will be illuminated.
1.2 External Power Supply
To power the board using an external power supply connected to J20 (EXT Supply 5VDC), the jumper at J21 (Power
Select) must be placed on the EXT position. In order for the board to be powered the switch at SW1 must be in the
ON position, when the board is powered, the LED at LD8 will illuminate. If SW1 is in the OFF position the UDB is not
powered. A fail to power can also occur if the jumper at J21 is in the USB position.
Connector J20 is a two pin header using 100mil spaced, 0.25mil square posts. An MTE style connector or clip leads
can be used to supply power to this header. The proper polarity is marked on the board. A Shotkey diode, D5, is
provided for reverse polarity protection.
1.3 Power Supply Circuit Description
All on-board circuits operate at 3.3V. The primary regulated power bus VCC3V3 is powered by a voltage regulator
circuit made up of IC9, a Microchip MCP1703 LDO voltage regulator and the associated input and output
capacitors C32, C33 and C34. This regulator is rated for a maximum dropout of 625mV. To ensure that the
regulator output is the proper 3.3V, the minimum voltage applied to the input of the regulator should be 4V.
Allowing for the forward drop across the reverse polarity protection diode, D5, in the input circuit, the minimum
external supply voltage should be 4.4V.
In addition to the main voltage regulator, a second regulator is used to provide power to the USB serial converter
circuit. This regulator is made up of IC11, a Microchip TC1014 LDO voltage regulator and the associated input and
output capacitors C28 and C29 and bypass capacitor C30. This regulator is always powered from the USB connector
J23, and therefore, power is only supplied to the USB serial converter when J23 is connected to a live USB port.
1.4
9V0 Power Supply for PIM/PICtail™ Plus Bus
Some Microchip PICtail™ Plus modules require a 9V power supply to power some of their functions. There is no 9V
power supply on the UDB board. If a PICtail™ Plus module is being used that requires the 9V power supply, an
external, regulated 9V supply can be attached at J5 to provide this voltage. Jumper J5 is an unloaded, two pin
header in the upper right corner of the board. Note the polarity marking on the board as it is not internally
protected from reverse polarity.