Tool/software:
Is it okay to over-drive the ports of the TCA9539-Q1 (configured as either an input or output) if the current is limited to < 20mA? The voltages could be as high as 35V but they are current limited by a large resistor in series with the expander ports (10k+).
Looking at the absolute maximum ratings it looks like the 20mA clamping current only applies to negative voltages on the input:
The datasheet is a little confusing on this, but given that the inputs are 5V tolerant, and referring to this note: 
I think it can be assumed there is no internal clamping diode to VCC.
Hi Jessica,
Sorry about that. I am thinking of a different I/O expander in our portfolio.
You are correct. TCA9539-Q1 does not have clamping diode from pin to VCC.
The recommended operating table suggests that the clamp diode does not exist. A VCC = 3.6V with input of 5.5V is allowed. If a clamping diode was put in place, the MAX value would most likely be set to VCC or a VCC + 0.5V.
In a similar I/O expander PCF8574, we show the clamping diode and it aligns with the recommended operating conditions in the datasheet:
Recommended operating:
Regards,
Tyler
