MAX3186
±15kV ESD-Protected, EMC-Compliant, 230kbps
RS-232 Serial Port for Modems
6 _______________________________________________________________________________________
Human Body Model
Figure 2a shows the Human Body Model, and Figure
2b shows the current waveform it generates when dis-
charged into a low impedance. This model consists of
a 100pF capacitor charged to the ESD voltage of inter-
est, which is then discharged into the device through a
1.5kΩ resistor.
IEC1000-4-2
The IEC1000-4-2 standard covers ESD testing and per-
formance of finished equipment; it does not specifically
refer to integrated circuits. The MAX3186 helps you
design equipment that meets Level 4 (the highest level)
of IEC1000-4-2, without additional ESD-protection com-
ponents.
The main difference between tests done using the
Human Body Model and IEC1000-4-2 is higher peak
current in IEC1000-4-2. Because series resistance is
lower in the IEC1000-4-2 ESD test model (Figure 1a),
the ESD withstand voltage measured to this standard is
generally lower than measured using the Human Body
Model. Figure 1b shows the current waveform for the
±8kV IEC1000-4-2 Level 4 ESD Contact-Discharge test.
The Air-Gap test involves approaching the device with a
charge probe. The Contact-Discharge method connects
the probe to the device before the probe is energized.
Machine Model
The Machine Model for ESD testing uses a 200pF stor-
age capacitor and zero-discharge resistance. It mimics
the stress caused by handling during manufacturing
and assembly. Of course, all pins (not just RS-232
inputs and outputs) require this protection during man-
ufacturing. Therefore, the Machine Model is less rele-
vant to the I/O ports than are the Human Body Model
and IEC1000-4-2.
__________Applications Information
Use proper layout to ensure other devices on your
board are not damaged in an ESD strike. Currents as
high as 60A can instantaneously pass into the ground,
so be sure to minimize the ground-lead return path to
the power supply. A separate return path to the power
supply is recommend. Trace widths should be greater
than 40 mils. Bypass V
CC
, V
DD
, and V
SS
with 0.1µF
capacitors as close to the part as possible to ensure
maximum ESD protection.
Tie any transmitter inputs to GND or V
CC
. No external
protection diodes are needed because the MAX3186 is
not sensitive to power-supply sequencing.
CHARGE-CURRENT
LIMIT RESISTOR
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
C
s
100pF
R
C
1M R
D
1500Ω
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
Figure 2a. Human Body ESD Test Model
I
P
100%
90%
36.8%
t
RL
TIME
t
DL
CURRENT WAVEFORM
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
I
r
10%
0
0
AMPERES
Figure 2b. Human Body Model Current Waveform
