ESD protection using a variable voltage supply clamp

Abstract

This paper discusses the advantages and limitations of using supply clamping networks for electrostatic discharge (ESD) protection of integrated circuits (ICs). In addition, this paper presents an innovative supply clamp circuit that attempts to address some of the limitations of the more traditional supply clamping methods. This new circuit varies its clamp voltage depending upon whether or not the IC is mounted in a printed circuit board. If the IC is not mounted the clamp voltage is set at a very low value for maximum ESD protection. However, once the IC is mounted, the clamp voltage is increased to a value greater than the supply voltage to avoid interfering in the normal operation of the IC. Voltage versus current (V/I) characteristics of this supply clamp circuit are compared for the mounted versus unmounted cases. In addition, human body model (HBM) ESD threshold levels are compared for protected versus unprotected ICs. HBM ESD thresholds were seen to increase from as low as 500 V to greater than 4000 V due to the addition of a protection network incorporating this clamp circuit.