An on-chip TVS design to meet system level ESD protection for RS485 transceiver

Abstract

RS485 interface is widely used in the area of industrial control and remote meter reading, which are often subjected to serious electrostatic damage. A new On-Chip TVS (OCT) structure without extra process modification and a novel electrostatic discharge method for RS485 transceiver IC have been proposed. It is composed of a serie of Zener diodes and fabricated in 5V/18V/24V 0.5µm CDMOS technology. A 100ns pulse width of the Transmission Line Pulsing (TLP) test is performed for this proposed OCT. The driver circuit itself can work as an ESD device as well. The OCT trigger voltage is compatible with the signal level of RS485 standard. The OCT device protection level of human-body-model (HBM) is up to 16.34kV. RS485 transceiver integrated with OCT has also been tested in order to verify its reliability. The results indicate that it can pass the IEC61000-4-2 contact ±10kV stress and IEC 61000−4−4 Electrical Fast Transient (EFT) ±2.2kV without any hard damages and latch-up issues. The RS485 transceiver integrated with the OCT allows error-free data rate transfer up to 500 kbps. The chip occupies a silicon area of 2.4×1.17mm².