down is typically 100µs, as shown in Figure 2. Connect
SHDN to V
CC
if the shutdown mode is not used.
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electro-
static discharges encountered during handling and
assembly. The driver outputs and receiver inputs of the
MAX3385E have extra protection against static electric-
ity. Maxim’s engineers have developed state-of-the-art
structures to protect these pins against ESD of ±15kV
without damage. The ESD structures withstand high
ESD in all states: normal operation, shutdown, and
powered down. After an ESD event, Maxim’s “E” ver-
sions keep working without latchup, whereas compet-
ing RS-232 products can latch and must be powered
down to remove latchup.
ESD protection can be tested in various ways; the
transmitter outputs and receiver inputs of this product
family are characterized for protection to the following
limits:
1) ±15kV using the Human Body Model
2) ±8kV using the contact-discharge method specified
in IEC 1000-4-2
3) ±15kV using IEC 1000-4-2’s air-gap method.
ESD Test Conditions
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents
test setup, test methodology, and test results.
Human Body Model
Figure 3a shows the Human Body Model, and Figure
3b 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 interest,
which is then discharged into the test device through a
1.5kΩ resistor.
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and per-
formance of finished equipment; it does not specifically
refer to integrated circuits. The MAX3385E helps you
design equipment that meets Level 4 (the highest level) of
IEC 1000-4-2, without the need for additional ESD-pro-
tection 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 4a shows the IEC 1000-4-2 model, and
Figure 4b 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 con-
nects the probe to the device before the probe is ener-
gized.
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. Of course, all pins require this protec-
tion 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, refer
to Table 2 for required capacitor values. Do not use val-
MAX3385E
±15kV ESD-Protected, 3.0V to 5.5V, Low-Power,
up to 250kbps, True RS-232 Transceiver
