8

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 IEC-1000 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.

IEC1000-4-2 Testing

The IEC 1000 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 7. TRANSMITTER OUTPUT VOLTAGE vs LOAD

CAPACITANCE

FIGURE 8. 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

1 TRANSMITTER AT 30kbps

LOAD CAPACITANCE (pF)

0

1000

2000

3000

4000

5000

5

10

15

20

25

+SLEW

-SLEW

ISL83385E