It is important to note that a device rated at IEC 61000-4-2 does
not guarantee the system will pass ESD testing. This is because
the IEC is a system level standard that was originally intended to be
applied as pass/fail criteria for showing system level ESD immunity.
The purpose of a protection device is to reduce a transient voltage
spike down to a safe voltage for the protected IC, and the best way
to insure that your TVS protection device adequately protects your
interface circuitry is by choosing components that offer the lowest
clamping voltage performance.

To illustrate the unique protection benefits of Semtech's proprietary
EPD technology, the following chart compares the clamping
voltage of an industry standard 5V TVS device with the clamping
voltage of the Semtech RClamp2504N device. Built on the EPD
platform, the RClamp2504N offers a very low 2.5V working voltage.
Notice that the Semtech RClamp2504N provides a nice low, flat
clamping voltage over a wide range of peak pulse current values.
As a 2.5V working voltage device, the clamping performance of
the RClamp2504N is significantly lower than the typical 5V TVS
protection device. As the sensitivity on next generation PHYs
increases, selecting TVS devices with a lower clamping voltage
as illustrated in the chart can impact the difference between
safeguarding an Ethernet PHY or resulting in catastrophic damage.

Introduction & Background