11

FN6040.1

July 8, 2005

without allowing any latchup mechanism to activate, and

don’t interfere with RS-232 signals as large as

±25V.

Human Body Model (HBM) Testing

As the name implies, this test method emulates the ESD

event delivered to an IC during human handling. The tester

delivers the charge through a 1.5k

Ω current limiting resistor,

making the test less severe than the IEC61000 test which

utilizes a 330

Ω limiting resistor. The HBM method

determines an ICs ability to withstand the ESD transients

typically present during handling and manufacturing. Due to

the random nature of these events, each pin is tested with

respect to all other pins. The RS-232 pins on “E” family

devices can withstand HBM ESD events to

±15kV.

IEC61000-4-2 Testing

The IEC61000 test method applies to finished equipment,

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-232 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 lower current limiting

resistor coupled with the larger charge storage capacitor yields

a test that is much more severe than the HBM test. The extra

ESD protection built into this device’s RS-232 pins allows the

design of equipment meeting level 4 criteria without the need

for additional board level protection on the RS-232 port.

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 “E” device RS-232 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. All “E” family devices survive ±8kV contact

discharges on the RS-232 pins.

FIGURE 12. TRANSMITTER OUTPUT VOLTAGE vs LOAD

CAPACITANCE

FIGURE 13. SLEW RATE vs LOAD CAPACITANCE

-6.0

-4.0

-2.0

0

2.0

4.0

6.0

1000

2000

3000

4000

5000

0

LOAD CAPACITANCE (pF)

1 TRANSMITTER AT 250kbps

OTHER TRANSMITTERS AT 30kbps

LOAD CAPACITANCE (pF)

0

1000

2000

3000

4000

5000

-SLEW

+SLEW

5

10

15

20

25

30

ISL83387E