ADM202E/ADM1181A
H IGH BAUD RATE
T he protection structure achieves ESD protection up to ±15 kV
and EFT protection up to ±2 kV on all RS-232 I/O lines. T he
methods used to test the protection scheme are discussed later.
T he ADM202E/ADM1181A feature high slew rates permitting
data transmission at rates well in excess of the EIA/RS-232-E
specifications. RS-232 voltage levels are maintained at data rates
up to 230 kb/s even under worst case loading conditions. T his
allows for high speed data links between two terminals or indeed
it is suitable for the new generation ISDN modem standards which
requires data rates of 230 kbps. The slew rate is internally con-
trolled to less than 30 V/µs in order to minimize EMI interference.
R1
RECEIVER
INPUT
RX
D1
R
IN
D2
ESD /EFT TRANSIENT P RO TECTIO N SCH EME.
T he ADM202E/ADM1181A use protective clamping structures
on all inputs and outputs which clamp the voltage to a safe level
and dissipate the energy present in ESD (Electrostatic) and
EFT (Electrical Fast T ransients) discharges. A simplified sche-
matic of the protection structure is shown in Figure 3. Each in-
put 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 as one or the other is reverse bi-
ased depending on the polarity of the signal. If however the volt-
age exceeds about 50 V in either direction, reverse breakdown
occurs and the voltage is clamped at this level. T he diodes are
large p-n junctions that are designed to handle the instanta-
neous current surge which can exceed several amperes.
Figure 3a. Receiver Input Protection Schem e
T
OUT
TRANSMITTER
RX
OUTPUT
D1
D2
Figure 3b. Transm itter Output Protection Schem e
T he transmitter outputs and receiver inputs have a similar pro-
tection structure. T he receiver inputs can also dissipate some of
the energy through the internal 5 kΩ resistor to GND as well as
through the protection diodes.
Typical Performance Curves
80
70
80
70
60
50
60
50
40
30
20
10
0
LIMIT
40
30
20
10
0
LIMIT
0.3
0.6
1
3
6
10
30
START 30.0 MHz
STOP 200.0 MHz
LOG FREQUENCY – MHz
Figure 4. EMC Radiated Em issions
Figure 5. EMC Conducted Em issions
REV. 0
–5–
ADI [ ADI ]
