ADM206E/ADM207E/ADM208E/ADM211E/ADM213E

REV. B

–10–

new generation modem standards which requires data rates of

200 kb/s. The slew rate is internally controlled to less than 30 V/

µs

in order to minimize EMI interference.

3V

0V

EN INPUT

VOH

VOL

RECEIVER

OUTPUT

VOH –0.1V

VOL +0.1V

NOTE:

EN IS THE COMPLEMENT OF

EN FOR THE ADM213E

Figure 22. Receiver-Disable Timing

3V

0V

EN INPUT

RECEIVER

OUTPUT

+3.5V

+0.8V

NOTE:

EN IS THE COMPLEMENT OF

EN FOR THE ADM213E

Figure 23. Receiver Enable Timing

ESD/EFT Transient Protection Scheme

The ADM2xxE uses protective clamping structures on all inputs

and outputs which clamps the voltage to a safe level and dissi-

pates the energy present in ESD (Electrostatic) and EFT (Elec-

trical Fast Transients) discharges. A simplified schematic of the

protection structure is shown in Figures 24a and 24b. Each

input and output contains two back-to-back high speed clamp-

ing diodes. During normal operation with maximum RS-232

signal levels, the diodes have no affect as one or the other is

reverse biased depending on the polarity of the signal. If how-

ever the voltage exceeds about

±50 V, reverse breakdown occurs

and the voltage is clamped at this level. The diodes are large p-n

junctions which are designed to handle the instantaneous cur-

rent 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 dis-

cussed later.

RX

D1

D2

RECEIVER

INPUT

R1

Figure 24a. Receiver Input Protection Scheme

RX

D1

D2

TRANSMITTER

OUTPUT

Figure 24b. Transmitter Output Protection Scheme

ESD TESTING (IEC1000-4-2)

IEC1000-4-2 (previously 801-2) specifies compliance testing

using two coupling methods, contact discharge and air-gap

discharge. Contact discharge calls for a direct connection to the

unit being tested. Air-gap discharge uses a higher test voltage

but does not make direct contact with the unit under test. With

air discharge, the discharge gun is moved towards the unit un-

der test developing an arc across the air gap, hence the term air-

discharge. This method is influenced by humidity, temperature,

barometric pressure, distance and rate of closure of the discharge

gun. The contact-discharge method while less realistic is more

repeatable and is gaining acceptance in preference to the air-gap

method.

Although very little energy is contained within an ESD pulse,

the extremely fast rise time coupled with high voltages can cause

failures in unprotected semiconductors. Catastrophic destruc-

tion can occur immediately as a result of arcing or heating. Even

if catastrophic failure does not occur immediately, the device

may suffer from parametric degradation which may result in

degraded performance. The cumulative effects of continuous

exposure can eventually lead to complete failure.

I-O lines are particularly vulnerable to ESD damage. Simply

touching or plugging in an I-O cable can result in a static dis-

charge that can damage or completely destroy the interface

product connected to the I-O port. Traditional ESD test meth-

ods such as the MIL-STD-883B method 3015.7 do not fully

test a products susceptibility to this type of discharge. This test

was intended to test a products susceptibility to ESD damage

during handling. Each pin is tested with respect to all other

pins. There are some important differences between the tradi-

tional test and the IEC test:

(a) The IEC test is much more stringent in terms of discharge

(

energy. The peak current injected is over four times greater.

(b) The current rise time is significantly faster in the IEC test.

(c) The IEC test is carried out while power is applied to the device.

It is possible that the ESD discharge could induce latch-up in the

device under test. This test therefore is more representative of a

real-world I-O discharge where the equipment is operating nor-

mally with power applied. For maximum peace of mind however,

both tests should be performed, therefore, ensuring maximum

protection both during handling and later during field service.