Altera DE2-115 maximum GPIO current

Altera_Forum · ‎05-15-2014

Hi, I've tried searching the forums for an answer to this question to no avail.

As I have seen in the quartus 2 tool the GPIO pins have a maximum current strength of 8mA or 16mA. Am I right to assume this is for continuous current?

I want to supply a short trigger signal and from simulation it turns out I need around 35mA or a bit more current from the GPIO pins, would I be able to draw that for say 1-2us?

Would it perhaps be possible to connect a few of the GPIO pins in parallel to supply this current?

Altera_Forum · ‎05-15-2014

Ganging outputs to drive higher currents is possible, but you must take care. There is a "switch through" current that can be just a big of an issue if you don't have the outputs timing closely matched. (There will always be some)

In Practice, what will happen is the output will not be able to reach the VOH levels, with the higher current draw. This may also damage the output depending on the duration due to thermal heating or metal migration issues.

35 mA is more than I would risk on a single output. I would tend to put an external driver or drive transistor in this case.

Pete

Altera_Forum · ‎05-16-2014

I strongly recommend you use external buffers/drivers to drive such a signal. Sourcing 35mA from an I/O pin might work for a bit but, I'm very sure, it'll soon fail.

The drive strength available is dependant on the I/O standard you select. Refer to the "I/O Standard Specifications" in the cyclone iv device datasheet (http://www.altera.com/literature/hb/cyclone-iv/cyiv-53001.pdf), page 1-12. To drive 35mA I suspect you're hoping to use one of the higher I/O voltages (perhaps 3.3V) for which you won't be able to select 16mA drive strength (through the Pin Planner). You can at 2.5V.

I agree with Anakha, ganging up pins can be considered. Ensure you switch them on the same clock edge and I doubt you'll run into any issues. However, although I can't find the detail at present, I'm very sure there is a limit as to how much current you can drive out of a bank of pins. Don't expect to create lots of groups all driving high currents. Your FPGA won't last as long as, I'm sure, you'd like it to.

Regards,

Alex