A trim/test interface in a packaged integrated circuit device prevents high through-current between pins of the IC device and trim/test interface digital logic within the IC device using a floating-pin-tolerant always-on CMOS input buffer. The always-on buffer uses a coupling capacitor at its input to block signals at DC and a weak-latch feedback path to ensure that intermediate or floating inputs are provided through the buffer only at one of two digital levels (e.g., those provided by a ground pin GND and by a high supply voltage pin VDD). The described interfaces and methods provide for false-entry-free test mode activation for IC devices with a low pin count, where there are a limited number of pins to cover all test/trim functions, or in which only analog, no-connect, or failsafe pins are available for trim or test mode entry control or trim or test data input.