fungus
October 3, 2012, 9:02pm
6
jpa:
The FPGA seems to have internal diodes to the 2.8V voltage rail. They limit at 3V, so the 5V ESD diode does not do much.
My concern is mostly >3V input voltages on the digital pins. The FPGA’s diodes should be adequate to limit that. I’m not sure about ESD, but as you said, it’s less likely to occur.
Just an update: I took my diode completely out and I’m sooooooo happy with the result! It now displays pretty much anything my Arduino can put out, no problem. I’ve been using it all day to debug/optimize a program to drive a TLC5940 and it’s brilliant! I couldn’t have done it with the diode in place…
As for the 5V->3.3 situation: Pretty much every Quad owner has probably fed 5V into their digital inputs and nothing seems to be happening. I also found this quote on this page: http://arduino.cc/playground/Main/I2CBi-directionalLevelShifter
Connecting the 5V Arduino directly to a single 3.3V-powered I2C chip usually works, even though it violates official specifications in multiple ways. In practice, Arduino’s internal pullups are so weak that ESD protection diodes inside the 3.3V chip limit the voltage.
(if any exceptions are discovered, where a chip is damaged or just doesn’t work properly, please edit this page)
So it seems quite common practice and nobody has problems.