±±5ꢀk EꢁDꢂ-rotected, 3.0k to 5.5k, Lowꢂ-ower,
up to 250ꢀbps, True Rꢁꢂ232 Transceiver
charged into a low impedance. This model consists of a
±11pF capacitor charged to the ESD voltage of interest,
5V/div
0
SHDN
which is then discharged into the test device through a
T2OUT
±.5ꢀΩ resistor.
IEC 1000-4-2
The IEꢁ ±111-4-2 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
IEꢁ ±111-4-2, without the need for additional ESD-pro-
tection components.
2V/div
0
T1OUT
V
= 3.3V
CC
C1–C4 = 0.1µF
The major difference between tests done using the
Human Body Model and IEꢁ ±111-4-2 is higher peaꢀ
current in IEꢁ ±111-4-2, because series resistance is
lower in the IEꢁ ±111-4-2 model. Hence, the ESD with-
stand voltage measured to IEꢁ ±111-4-2 is generally
lower than that measured using the Human Body
Model. Figure 4a shows the IEꢁ ±111-4-2 model, and
Figure 4b shows the current waveform for the 8ꢀV IEꢁ
±111-4-2 Level 4 ESD contact-discharge test.
40µs/div
Figure 2. Transmitter Outputs Exiting Shutdown or
Powering Up
down is typically ±11µs, as shown in Figure 2. ꢁonnect
SHDN to V if the shutdown mode is not used.
ꢁꢁ
±±5ꢀk EꢁD -rotection
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.
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 ±±5ꢀV
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 ꢀeep worꢀing without latchup, whereas compet-
ing RS-232 products can latch and must be powered
down to remove latchup.
Machine Model
The Machine Model for ESD tests all pins using a
211pF 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 Pꢁ board assembly, the
Machine Model is less relevant to I/O ports.
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:
Applications Information
Capacitor ꢁelection
The capacitor type used for ꢁ±–ꢁ4 is not critical for
proper operation% polarized or nonpolarized capacitors
can be used. The charge pump requires 1.±µF capaci-
tors for 3.3V operation. For other supply voltages, refer
to Table 2 for required capacitor values. Do not use val-
±) ±±5ꢀV using the Human Body Model
2) ±8ꢀV using the contact-discharge method specified
in IEꢁ ±111-4-2
3) ±±5ꢀV using IEꢁ ±111-4-2’s air-gap method.
Table 2. Required Minimum Capacitance
Values
ESD Test Conditions
ESD performance depends on a variety of conditions.
ꢁontact Maxim for a reliability report that documents
test setup, test methodology, and test results.
V
CC
C1, C
C2, C3, C4
(µF)
BYPASS
(V)
(µF)
Human Body Model
Figure 3a shows the Human Body Model, and Figure
3b shows the current waveform it generates when dis-
3.1 to 3.6
4.5 to 5.5
3.1 to 5.5
1.±
1.147
1.±
1.±
1.33
1.47
6
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