Transient Response of ESD Protection Devices for a High-Speed I/O Interface

Abstract

System-efficient electrostatic discharge (ESD) design (SEED) models of a diode and transient voltage suppressor (TVS) were developed to study their transient response in a high-speed input/output interface. Previously reported SEED models were improved to strengthen their convergence stability and facilitate accurate predictions over a wide range of conditions. These improvements were required to accurately capture the race conditions between the TVS and <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -chip diode, where the diode's turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> may prevent turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> of the TVS. Simulations and measurements were performed to demonstrate the impact of the ESD pulse's rise time on race conditions. During a race, results showed the worst-case quasi-static diode current could be twice as high for long rise-time pulses than for short rise-times where the TVS does not turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> , and <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -chip diode current may be larger at low test voltages than at high test voltages where the TVS does turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> . Adding a small passive impedance between the external TVS and the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -chip diode helps the TVS turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and reduce the current through the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -chip diode by more than 50%. Similarly, lengthening the trace between the TVS and diode could reduce <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -chip diode current by up to a factor of two.