3V, ±15kV ESD-Protected, AutoShutdown Plus
RS-232 Transceiver for PDAs and Cell Phones
MAX3387E
R
C
50M to 100M
CHARGE-CURRENT
LIMIT RESISTOR
HIGH-
VOLTAGE
DC
SOURCE
R
D
330Ω
DISCHARGE
RESISTANCE
DEVICE
UNDER
TEST
I
100%
90%
I
PEAK
Cs
150pF
STORAGE
CAPACITOR
10%
Figure 6a. IEC 1000-4-2 ESD Test Model
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and
performance of finished equipment; it does not specifi-
cally refer to ICs. The MAX3387E helps you design
equipment that meets Level 4 (the highest level) of IEC
1000-4-2, without the need for additional ESD-protec-
tion components.
The major difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak
current in IEC 1000-4-2 because series resistance is
lower in the IEC 1000-4-2 model. Hence, the ESD with-
stand voltage measured to IEC 1000-4-2 is generally
lower than that measured using the Human Body
Model. Figure 6a shows the IEC 1000-4-2 model, and
Figure 6b shows the current waveform for the ±8kV IEC
1000-4-2 Level 4 ESD Contact Discharge test.
The air-gap test involves approaching the device with a
charged probe. The contact-discharge method connects
the probe to the device before the probe is energized.
t R = 0.7ns to 1ns
t
30ns
60ns
Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform
Table 2. Minimum Required Capacitor
Values
V
CC
(V)
3.0 to 3.6
4.5 to 5.5
3.0 to 5.5
C1
(µF)
0.1
0.047
0.22
C2, C3, C4
(µF)
0.1
0.33
1
Machine Model
The Machine Model for ESD tests all pins using a
200pF storage capacitor and zero discharge resis-
tance. Its objective is to emulate the stress caused by
contact that occurs with handling and assembly during
manufacturing. All pins require this protection during
manufacturing, not just RS-232 inputs and outputs.
Therefore, after PC board assembly, the Machine
Model is less relevant to I/O ports.
Applications Information
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; polarized or nonpolarized capacitors
can be used. The charge pump requires 0.1µF capaci-
tors for 3.3V operation. For other supply voltages, see
Table 2 for required capacitor values. Do not use val-
ues smaller than those listed in Table 2. Increasing the
capacitor values (e.g., by a factor of 2) reduces ripple
on the transmitter outputs and slightly reduces power
consumption. C2, C3, and C4 can be increased without
changing C1’s value. However, do not increase C1
without also increasing the values of C2, C3, and C4 to
maintain the proper ratios (C1 to the other capacitors).
When using the minimum required capacitor values,
make sure the capacitor value does not degrade
excessively with temperature. If in doubt, use capaci-
tors with a larger nominal value. The capacitor’s equiva-
lent series resistance (ESR), which usually rises at low
temperatures, influences the amount of ripple on V+
and V-.
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