Designers often ask questions about the capability of an operational amplifier to withstand electrical overstress. These questions tend to focus on the device inputs, but can involve the supply voltage pins or even the output pin. Each of these different pin functions have electrical stress limits determined by the voltage breakdown characteristics of the particular semiconductor fabrication process and specific circuits connected to the pin. Additionally, internal electrostatic discharge (ESD) protection is built into these circuits to protect them from accidental ESD events both before and during product assembly.

Having a good understanding of this basic ESD circuitry and the relevance to an electrical overstress event is helpful. Figure 7-7 shows the ESD circuits contained in the INA500 devices. On the input pins, the ESD protection circuitry involves local high impedance diode structures and do not route the ESD current to power supply ESD cell. On the output pin, there are reverse biased diodes to both the power supply rails. These diode structures route the ESD current back to the internal power supply lines, where there is an absorption power supply ESD cell internal to the difference amplifier. On the reference pin, the ESD protection is local and does not route current to the power supply ESD cell.

All of the ESD protection circuitry is intended to remain inactive during normal circuit operation.

Figure 7-7 Equivalent Internal ESD Circuitry