Hello all,
Can someone tell me what is the function of the COM pin (pin 10) on a ULN2803A Darlington Driver IC? Here's the datasheet if you need it:
http://focus.ti.com/lit/ds/symlink/uln2803a.pdfI've seen schematics which connects the COM pin to Vcc, but I don't see why. The drivers can only sink currents, not source any, so I don't think we need to supply Vcc. I've also tried to understand it by looking at the logic diagram, but still can't make any sense out of it.
I've also tried connecting an LED to one of the outputs, and then tried connecting COM to Vcc and also leaving it hanging. Both have the same results; the LED lit.
Then I also tried connecting COM to Vcc, LED's anode to output and LED's cathode to ground. The LED didn't light up, confirming that the driver only sinks current.
Can anyone help me here? I really need to know this.
Thanks.