Low-power, tristate, off-chip driver circuit

Abstract

An output driver circuit for a semiconductor chip has a push-pull output with a P-channel pull-up and an N-channel pull-down. Predrivers produce push-pull outputs for driving the gates of the output driver. Compensator circuits, one for the N-channel pull-down, and one for the P-channel pull-up, are used to prevent the transition from high-to-low or low-to-high from being too rapid, which could cause noise due to inductance of the package leads. A feedback circuit halts the operation of the compensator circuits after a short interval. An overvoltage circuit formed in a well of the semiconductor chip holding the driver circuit, having an input coupled to receive the data output of the predriver circuit going to the P-channel pull-up, also functions to prevent damage to the output driver circuit due to overvoltage on the output node. A stack of diodes connected in a forward direction between the N-well of the P-channel pull-up transistor and the positive terminal of the voltage supply serves to clamp the output node if it tends to go above a selected overvoltge level.