# Electronic – When is it okay to exceed the absolute maximum rating on a part

datasheetmaximum-ratingsvoltage

I've always thought that the absolute maximum ratings on a part are the limits that thou shalt not violate. Period. End of story.

However, another engineer is making the case that it's okay to exceed the absolute max rating for the input voltage on a microcontroller I/O pin. Specifically, he wants to apply 5v, current limited to 30uA, to a micro with an absolute max voltage of 3.8v (Vdd + 0.3V <= 3.9V). The argument being the clamp diodes will take care of the excess voltage.

I couldn't find anything in the datasheet about the I/O hardware on the micro.

When is it okay to exceed the absolute maximum rating on a part?

Datasheet

User Guide

In the case you specify, you've identified that the absolute maximum ratings are probably an approximation. Its plausible that \$\mu A\$ currents with a high drive impedance can be accepted on the pins quite reliably without exceeding the breakdown voltages (and arguably you don't exceed the rating like this, since the pin will clamp). There is additionally the risk of latch-up if unexpected parts of the silicon are conducting with various voltage states.