I'm planning to use a ULN2003 7-way darlington driver as an input/output isolator for a FPGA with 3.3v I/O. The input interface has pullups from the collectors to 3.3v supply, and the output base inputs are driven by the gate array output lines, and switch loads (relays and LEDs) to a 12vdc supply. Total i/o count is 6, so one 2003 will do the job, however I'm wondering whether the common diodes on the collectors inside the 2003, combined with the dual voltages involved, might pose a problem. If the diodes were 'perfect' the situation would be OK, but things aren't often that easy in the real world.
Can anyone see any shortcomings? TIA
Ascii schematic for clarification follows.
3V3 3V3 | | | 12VDC .-. | \ | | | _ o o | | .----------------. )| '-' | | )| |---------| | _)| | | | |/ | FPGA | |/ -| | |----| |> | | |>| | | | | | '----------------' (created by AACircuit v1.28.6 beta 04/19/05