Transient supply clamp with a variable RC time constant

Abstract

This paper summarizes several basic supply clamping techniques and presents an innovative transient clamp circuit that makes use of some properties of a variable voltage clamp. This circuit varies its RC time constant dependent upon whether or not the integrated circuit (IC) is mounted on a printed circuit (PC) board. If the IC is mounted the time constant of the transient clamp is set very short so it will not interfere in the normal operation of the device. However, if the IC is free standing the RC time constant is set much longer to ensure the clamp will stay on long enough to discharge the entire ESD pulse should the need arise. This clamp circuit was used as a component in the electrostatic discharge (ESD) protection network for an analog intermediate frequency (IF) limiter IC. Human Body Model (HBM) ESD levels increased from less then 300 volts to greater then 2000 volts due to the addition of this protection network.