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

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
on
-chip diode, where the diode's turn
on
may prevent turn
on
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
on
, and
on
-chip diode current may be larger at low test voltages than at high test voltages where the TVS does turn
on
. Adding a small passive impedance between the external TVS and the
on
-chip diode helps the TVS turn
on
and reduce the current through the
on
-chip diode by more than 50%. Similarly, lengthening the trace between the TVS and diode could reduce
on
-chip diode current by up to a factor of two.