ADM202E/ADM1181A
HIGH BAUD RATE
The 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. This
allows for high speed data links between two terminals or indeed
it is suitable for the new generation I
SDN
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.
ESD/EFT TRANSIENT PROTECTION SCHEME.
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 later.
RECEIVER
INPUT
R1
D1
R
IN
D2
RX
The 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 Transients) 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. The diodes are
large p-n junctions that are designed to handle the instanta-
neous current surge which can exceed several amperes.
The transmitter outputs and receiver inputs have a similar pro-
tection structure. The receiver inputs can also dissipate some of
the energy through the internal 5 kΩ resistor to GND as well as
through the protection diodes.
Figure 3a. Receiver Input Protection Scheme
T
OUT
D1
D2
RX
TRANSMITTER
OUTPUT
Figure 3b. Transmitter Output Protection Scheme
Typical Performance Curves
80
70
60
50
80
70
60
50
LIMIT
LIMIT
dBµV
40
30
20
10
0
START 30.0 MHz
STOP 200.0 MHz
dBµV
40
30
20
10
0
0.3
0.6
1
3
6
LOG FREQUENCY – MHz
10
30
Figure 4. EMC Radiated Emissions
Figure 5. EMC Conducted Emissions
REV. 0
–5–
AD [ ANALOG DEVICES ]
