Typical CMOS ESD Protection

Some integrated circuits feature built in protection by means of an internal SCR or resistor and diode network. The basic requirement of a CMOS ESD protection network is that it provide a low impedance path for the discharge energy while limiting the current and voltage seen by the active circuit. This means that the transient energy is dissipated in the transceiver itself. The basic input protection circuit usually consists of the following elements: 

  • A shunt device to discharge positive polarity transients
  • A shunt device to discharge negative polarity transients
  • A series element for current limiting

When an ESD voltage is applied to the input structure, the on-chip diodes shunt the transient current to the power line (VCC) or ground. A positive transient voltage causes diode D1 to be forward biased when the input voltage exceeds VCC. Likewise, for negative transients, Diode D2 shunts the negative current. The polysilicon input resistors serve to limit the peak currents. Since polysilicon resistors are thermally insulated by a surrounding layer of SiO2 or glass they are particularly susceptible to thermal damage resulting from joule heating by ESD induced currents. A typical CMOS input protection circuit can provide ESD immunity to approximately 4kV.

But is built-in CMOS ESD protection alone good enough in your designs? To learn more about this topic, view the application note linked below.

> Download our "CMOS ESD Protection" application note

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