ADM202E/ADM1181A
Rev. C | Page 7 of 16
ESD/EFT TRANSIENT PROTECTION SCHEME
The ADM202E/ADM1181A use protective clamping structures
on all inputs and outputs to clamp the voltage to a safe level and
dissipate the energy present in electrostatic (ESD) and electrical
fast transients (EFT) discharges. A simplified schematic of the
protection structure is shown in Figure 8 and Figure 9. Each
input and output contains two back-to-back high speed
clamping diodes. During normal operation with maximum
RS-232 signal levels, the diodes have no effect because one or
the other is reverse biased depending on the polarity of the signal.
However, if the voltage exceeds about 50 V in either direction,
reverse breakdown occurs and the voltage is clamped at this level.
The diodes are large p-n junctions that are designed to handle
instantaneous current surges that exceed several amperes.
The transmitter outputs and receiver inputs have a similar
protection structure. The receiver inputs can dissipate some of
the energy through the internal 5 kΩ resistor to GND, as well as
through the protection diodes.
The protection structure achieves ESD protection up to ±15 kV
and EFT protection up to ±2 kV on all RS-232 I/O lines. The
methods used to test the protection scheme are discussed in the
ESD Testing (IEC1000-4-2) and Fast Transient/Burst Testing
(IEC1000-4-4) sections.
R
IN
R
X
D1
D2
RECEIVER
INPUT
R1
00066-008
Figure 8. Receiver Input Protection Scheme
R
X
D1
D2
TRANSMITTER
OUTPUT
T
OUT
00066-009
Figure 9. Transmitter Output Protection Scheme
