Hi. I have some question about SAMD21. PA24 and PA25 pins are for USB. But documentations says that this MC is working on 1.62-3.63 V. Accordingly, is it correct to connect UBS D+ and D- to this pins directly without some voltage drop from 5V to 3.3V for example. I know that SAMD21 on 3.3V works with directly connected D+ and D-, but is it legal? Will the microcontroller damaged when connected for a long time or not?
No. Those pins are designed to use a USB signal and USB signals are 5V. There is some sort of level conversion inside the chip.
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Thanks!
Um. USB signals are 3.3V USB Voltage Levels – IBEX Resources
VUSB (the software implementation of USB for AVRs) requires zeners on the data signals to limit their voltage.
I think the rest of Mike's message is correct, though - those pins are designed to connect directly to USB regardless of supply voltage. There are various places in the datasheet that exclude them from the usual pin limitations (but NOT the section on "absolute max pin voltage." Hopefully that's a datasheet error!)
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