ESD protection circuit for different power supplies
 A voltage clamping circuit that protects integrated circuits having multiple separate power supply voltage terminals from damage when an ESD event causes excessive differential voltages between the multiple separate power supply voltage terminals. The voltage clamping circuit has two subgroups of Darlington connected clamping transistors. The first subgroup of Darlington connected clamping transistors is connected between the first power supply voltage terminal and the second power supply voltage terminal. If the differential voltage exceeds the first clamping voltage level, the first subgroup of Darlington connected clamping transistors turn on and restore the first differential voltage to a level less than the first clamping voltage level. The second subgroup of Darlington connected clamping transistors connected between the second power supply terminal and the first power supply terminal. If the differential voltage exceeds the second clamping voltage level, the second subgroup of Darlington connected transistors turn on and restore the differential voltage to a level less than the second clamping voltage level. 
Taiwan Semiconductor Manufacturing Company
H
H01L
inventional
Jian-Hsing Yi-Hsun Jiaw-Ren Jing-Meng
Lee Wu Shih Liu