Part Number: SN74LVC1T45
I have a situation where the 74LVC1T45 is used as a level shifter in the serial comms line between two separate pieces of equipment. The problem is that the 74LVC1T45 "B" side (which is configured as an output) is powered from 3.3V (ie VCCB is 3.3V, as would be expected to create a normal 3.3V output signal), but at the other end of the comms line (in the second piece of equipment), there is a pullup to 5V. This pullup is impressing a 5V level onto the comms line, which feeds back to the 74LVC1T45 "B" side output, and this 5V level violates the abs max spec for an output not in a HiZ or power-off state, where the limit (as shown below) is VCCB+0.5V = 3.8V (obviously lower than the 5V being applied by the pullup in the other piece of equipment).
My question is what might be getting damaged in this situation? What are the real reliability risks - can they be quantified? In practice, this scenario has functioned successfully and without any known issues in multiple products that we have shipped - in other words, it does not appear to be a problem. But there must be a reason for that limit in the Abs Max spec, please can you explain what this reason might be? Unfortuately the data sheet for the part does not inclue a detailed configuration of the internal mosfets, so I cannot deduce anything for myslef. Thank you for your assistance!
