Honored Contributor
Honored Contributor4-4.2V sounds very like protection diodes kicking in.
You can look at the guidelines for enabling/disabling clamp diodes - page 3-2 of the "max 10 general purpose i/o user guide (max 10 general purpose i/o user guide)". You can potentially disable them. However... Which MAX 10 document have found that states you can use the I/O of MAX 10 directly as open drain operating at 5V? Refer to Table 2-4, on page 2-14 of the same "MAX 10 General Purpose I/O User Guide". The 'Open Drain' row states the I/O standards MAX 10 supports. There's nothing about operating at 5V. There's also the 'Maximum Allowed Overshoot' table in the "max 10 fpga device datasheet (https://www.altera.com/en_us/pdfs/literature/hb/max-10/m10_datasheet.pdf)". You can over-drive a pin to 4.12V indefinitely, but not much higher without risking damage to the device. You really need an external fet... Cheers, Alex
