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http://www.union-ic.com Rev.07 Sep.2015

10/13

UM3352E

IEC61000-4-2 Testing

The IEC61000 test method applies to finished equipments, rather than to an individual IC. Therefore,

the pins most likely to suffer an ESD event are those that are exposed to the outside world (the

RS-485 pins in this case), and the IC is tested in its typical application configuration (power applied)

rather than testing each pin-to-pin combination. The IEC61000 standard’s lower current limiting

resistor coupled with the larger charge storage capacitor yields a test that is much more severe than

the HBM test.

Air-Gap Discharge Test Method

For this test method, a charged probe tip moves toward the IC pin until the voltage arcs to it. The

current waveform delivered to the IC pin depends on approach speed, humidity, temperature, etc., so

it is difficult to obtain repeatable results. The UM3352E RS-485 pins withstand ±15kV air-gap

discharges.

Contact Discharge Test Method

During the contact discharge test, the probe contacts the tested pin before the probe tip is energized,

thereby eliminating the variables associated with the air-gap discharge. The result is a more

repeatable and predictable test, but equipment limits prevent testing devices at voltages higher than

±8kV. The RS-485 pins of all the UM3352E versions survive ±8kV contact discharges.

Typical Applications

The UM3352E transceivers are designed for bidirectional data communications on multipoint bus

transmission lines. To minimize reflections, the line should be terminated at both ends in its

characteristic impedance, and stub lengths of the main line should be kept as short as possible.