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 1.5kΩ current limiting resistor,
making the test less severe than the IEC61000 test which
utilizes a 330Ω 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.
Typical Performance Curves V
CC
= V
L
= 3.3V, T
A
= 25
o
C
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 50000
LOAD CAPACITANCE (pF)
TRANSMITTER OUTPUT VOLTAGE (V)
1 TRANSMITTER AT 250kbps
V
OUT
+
V
OUT
-
OTHER TRANSMITTERS AT 30kbps
LOAD CAPACITANCE (pF)
SLEW RATE (V/µs)
0 1000 2000 3000 4000 5000
-SLEW
+SLEW
5
10
15
20
25
30
ISL83387E
