This paper describes a new technique for the design of 3-terminal regulators in which the output voltage level can be adjusted without additional terminals or extra off-chip components. This circuit restricts the increase in the number of terminal pins by using a pin as both a voltage supply output and a voltage setup input. The voltage setup information is introduced using a serial control signal from outside the chip. Using the intermediate voltage level between the supply voltage and the regulator output, the adjustment data in the internal nonvolatile memory are safely updated without noise disturbance. To input the setup information into the chip in a stable manner, we developed a new 1-wire serial interface which combines key pattern matching and burst signal detection. To ensure high reliability, we suggested a quantitative method for evaluating the influence of noise in our new interface using a simple model with superimposed random noise. Circuits additional to those for a conventional 3-terminal regulator, include a 1-wire serial communication circuit, a low-capacity non-volatile memory, and a digital to analog (D/A) converter. A test chip was developed using 0.35µm standard CMOS process, and there was almost no overhead to the conventional 3-terminal regulator in both chip area and power dissipation. In an on-board test with the test chip, we confirmed successful output voltage adjustment from 1.0V to 2.7V with approximately 6.5mV precision.