ADM1181 Analog Devices, ADM1181 Datasheet - Page 5

• Manufacturer Part Number: ADM1181
• Description: EMI/EMC Compliant/ +-15 kV ESD Protected/ RS-232 Line Drivers/Receivers
• Manufacturer: Analog Devices

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
requires data rates of 230 kbps. The slew rate is internally con-
trolled to less than 30 V/ s in order to minimize EMI interference.
ESD/EFT TRANSIENT PROTECTION SCHEME.
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 k resistor to GND as well as
through the protection diodes.
Typical Performance Curves
REV. 0
80
70
60
50
40
30
20
10
0
START 30.0 MHz
Figure 4. EMC Radiated Emissions
SDN
STOP 200.0 MHz
modem standards which
LIMIT
–5–
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.
Figure 3b. Transmitter Output Protection Scheme
Figure 3a. Receiver Input Protection Scheme
80
70
60
50
40
30
20
10
0
RECEIVER
Figure 5. EMC Conducted Emissions
INPUT
0.3
RX
0.6
LOG FREQUENCY – MHz
1
ADM202E/ADM1181A
R1
D1
D2
T
OUT
R
3
IN
6
D2
D1
TRANSMITTER
OUTPUT
10
RX
30
LIMIT