ADM202E/ADM1181A

–5–

REV. 0

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

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 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

Ω 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 later.

RX

D1

D2

RECEIVER

INPUT

R1

Figure 3a. Receiver Input Protection Scheme

RX

D1

D2

TRANSMITTER

OUTPUT

Figure 3b. Transmitter Output Protection Scheme

Typical Performance Curves

START 30.0 MHz

STOP 200.0 MHz

LIMIT

80

70

60

50

40

30

20

10

0

Figure 4. EMC Radiated Emissions

LOG FREQUENCY – MHz

80

70

0

0.3

30

0.6

1

60

50

10

40

30

20

36

10

LIMIT

Figure 5. EMC Conducted Emissions