AN654 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

AN654

New RS-232 ICs Feature 1µA Supply Current, ±15kV ESD Protection, and 3V Operation

Maxim Integrated 

But, neither method can accurately assess the reliability of an IC connected to the outside world. Both

methods rate an IC according to the lowest-voltage failure on any pin, which is not an adequate test if the

device includes I/O pins. I/O pins usually require (and often have) higher levels of ESD protection than do

other pins.

As an example, an IC's I/O pins might withstand ±15kV while its other pins withstand only ±2kV. The two

methods above would therefore rate the IC for only ±2kV. To resolve this problem, manufacturers are

using a newer test method-IEC 801-2 (a test developed by the European community)-for rating RS-232 ICs

and other devices that connect directly to the "outside world." As a result, the successful completion of IEC

801-2 may soon become a necessary condition for selling equipment in Europe.

Newer ESD Test Method

Although originally intended as an equipment-level test for Europe, IEC 801-2 is now gaining acceptance

worldwide as the most appropriate ESD test for IC pins accessible to users of end equipment. The IEC 801-

2 method, unlike the two previous ones, tests only I/O pins. A device's ESD rating with this method,

therefore, is determined solely by the protection afforded by its I/O pins.

IEC 801-2 specifies ESD testing by either contact discharge or air-gap discharge. The commission prefers

contact discharge, though this represents a compromise. An ESD event caused by actual contact is more

repeatable, but less realistic. Air-gap discharge is more realistic, but varies widely in amplitude according

to temperature, humidity, barometric pressure, distance, and rate of closure with the IC.

IEC 801-2 defines four levels of compliance (Table B), according to the lowest-maximum voltage

withstood by the I/O pins. The levels accommodate both contact and air-gap discharge. Maxim's ICs meet

the highest level (level four) for contact and air-gap discharge, and are the only RS-232 ICs to achieve this

level of protection.

Table B. IEC 801-2 Compliance Levels

Testing ICs for ESD ruggedness requires the use of an "ESD gun." The gun allows testing with either

contact or air-gap discharge. Contact discharge requires physical contact between the gun and the IC before

the test voltage is applied. Air-gap discharge, on the other hand, requires the gun to be charged with the test

voltage before approaching the IC (from the perpendicular, and as fast as possible). The second technique

produces a spark at some critical distance from the test unit.

ESD produced by air-gap discharge resembles actual ESD events. But, like actual ESD, the air-gap

discharge variety is not readily duplicated. It depends on many variables that are not easily controlled. IEC

801-2 therefore recommends the contact-discharge technique, attesting to the general importance of

repeatability in testing. In either case, the test procedure calls for at least ten discharges at each test level.

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