8

±15kV ESD Protection

All pins on ISL8XXX devices include ESD protection

structures, but the ISL8XXXE family incorporates advanced

structures which allow the RS-232 pins (transmitter outputs

and receiver inputs) to survive ESD events up to

±15kV. The

RS-232 pins are particularly vulnerable to ESD damage

because they typically connect to an exposed port on the

exterior of the finished product. Simply touching the port

pins, or connecting a cable, can cause an ESD event that

might destroy unprotected ICs. These new ESD structures

protect the device whether or not it is powered up, protect

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 IC’s 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.

TABLE 3. LOGIC FAMILY COMPATIBILITY WITH VARIOUS

SUPPLY VOLTAGES

SYSTEM

POWER-SUPPLY

VOLTAGE

(V)

SUPPLY

VOLTAGE

(V)

COMPATIBILITY

3.3

3.3

Compatible with all CMOS

families.

5

5

Compatible with all TTL and

CMOS logic families.

5

3.3

Compatible with ACT and HCT

CMOS, and with TTL.

incompatible with AC, HC, and

CD4000 CMOS inputs.

FIGURE 7. TRANSMITTER OUTPUT VOLTAGE vs LOAD

CAPACITANCE

FIGURE 8. SLEW RATE vs LOAD CAPACITANCE

-6

-4

-2

0

2

4

6

1000

2000

3000

4000

5000

0

LOAD CAPACITANCE (pF)

TRANSMITTER AT 250kbps

LOAD CAPACITANCE (pF)

0

1000

2000

3000

4000

5000

5

10

15

20

25

+SLEW

-SLEW

ISL83220E