The device under protection (DUP) should not be degraded or destroyed in the event of an ESD strike

When ESD energy enters a circuit, an ESD protection diode turns on, shunting large current to GND. The voltage across the diode during an ESD event is defined as clamp voltage, VC. While the ESD protection diode is on, it can be regarded as being connected in parallel with the device under protection (DUP). It should be noted that a small amount of time is required for the ESD protection diode to turn on.
Therefore, ESD energy is applied to the DUP until the ESD protection diode turns on. Even after the ESD protection diode turns on, a voltage lower than its reverse breakdown voltage is applied to the DUP. The currents that flow to the ESD protection diode and the DUP are inversely proportional to their respective impedances. The impedance of the ESD protection diode during the “on” state is defined as dynamic resistance.

There are various types of ESD protection devices. ESD protection diodes have the following characteristics:

• Even low-capacitance diodes provide low dynamic resistance, which is a figure of merit for ESD protection.
• ESD protection diodes turn on quickly in the event of an ESD strike.
• ESD protection diodes do not deteriorate even after multiple ESD strikes.
  
  

Figure 5 compares the performance of three ESD protection diodes with different clamp voltage (VC) specifications, showing the voltage measured at the input of the DUP after an ESD entry. Figure 5 should be considered merely as a guide as these waveforms are the results of ESD application to a connector, not to the end of an antenna. Although the DF2B5M5SL and DF2B5M4SL provide similar clamp voltages (VC), their first peak voltages differ roughly by 50%.