MAX3443E Datasheet, PDF (11/15 Pages) Maxim Integrated Products – ±60V Fault-Protected, 10Mbps, Fail-Safe RS-485 Transceiver with ±15kV ESD Protection

±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
1MR^C9
1.R5^Dk9
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
HIGH-
VOLTAGE
DC
SOURCE
Cs
100pF
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
Figure 9a. Human Body ESD Test Model
Human Body Model
Figure 9a shows the Human Body Model, and Figure
9b 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.
IEC 1000-4-2
Since January 1996, all equipment manufactured and/or
sold in the European community has been required to
meet the stringent IEC 1000-4-2 specification. The IEC
1000-4-2 standard covers ESD testing and performance
of finished equipment; it does not specifically refer to inte-
grated circuits. The MAX3443E helps you design equip-
ment that meets Level 4 (the highest level) of IEC
1000-4-2, without additional ESD-protection components.
The main 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 ESD test model (Figure 10a),
the ESD withstand voltage measured to this standard is
generally lower than that measured using the Human
I_P 100%
90%
Ir
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPERES
36.8%
10%
0
0 _tRL
TIME
t_DL
CURRENT WAVEFORM
Figure 9b. Human Body Model Current Waveform
Body Model. Figure 10b 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 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. All pins (not just RS-485 inputs) require
this protection during manufacturing. Therefore, the
Machine Model is less relevant to the I/O ports than are
the Human Body Model and IEC 1000-4-2.
Driver Output Protection
Two mechanisms prevent excessive output current and
power dissipation caused by faults, or bus contention.
The first, a foldback current limit on the driver output
stage, provides immediate protection against short cir-
cuits over the whole common-mode voltage range. The
second, a thermal shutdown circuit, forces the driver
R_C
50MΩ TO 100MΩ
CHARGE-CURRENT-
LIMIT RESISTOR
R_D
330Ω
DISCHARGE
RESISTANCE
I
100%
90%
HIGH-
DEVICE
VOLTAGE
Cs
STORAGE
UNDER
DC
150pF
CAPACITOR
TEST
SOURCE
10%
tr = 0.7ns TO 1ns
30ns
t
60ns
Figure 10a. IEC 1000-4-2 ESD Test Model
Figure 10b. IEC 1000-4-2 ESD Generator Current Waveform
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