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I am trying to drive IR leds out of spartan 3E fpga on xilinx's BASYS2 board. I will be using external current amplifier to drive the IR lEDs with control singal from the FPGA. I need to know the max output current rating per I/O pins on the BASYS board with spartan 3E board.

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    \$\begingroup\$ What does the data sheet say? \$\endgroup\$
    – Andy aka
    Commented Apr 2, 2014 at 7:48
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    \$\begingroup\$ If you don't understand the datasheet, at least link to it so we can help you \$\endgroup\$ Commented Apr 2, 2014 at 8:36

1 Answer 1

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Some important links:

Board datasheet: http://www.digilentinc.com/Data/Products/BASYS2/Basys2_rm.pdf

Board schematic: http://www.digilentinc.com/Data/Products/BASYS2/Basys2_sch.pdf

FPGA datasheet: http://www.xilinx.com/support/documentation/data_sheets/ds312.pdf

I assume that you are talking about the I/O pins on JA, JB, JC, or JD. If you are asking about other I/O pins the answer may be different.

First, the max output current varies depending on how the FPGA is configured. It can be configured to support a max of 16 mA output current. To support this max current the outputs should be configured as LVCMOS33 with 16 mA output drive.

Second, note that these I/O pins have a 200 ohm resistor in series. This will reduce the voltage on these I/O pins as you increase the current.

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