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ADM3307E/ADM3310E/ADM3311E/ADM3312E/ADM3315E

Data Sheet

Rev. I | Page 16 of 24

The transmitter outputs and receiver inputs have a similar

protection structure. The receiver inputs can also dissipate some

of the energy through the internal 5 kΩ (or 22 kΩ for the

ADM3310E) resistor to GND as well as through the protection

diodes.

RIN

RECEIVER

INPUT

Figure 30. Receiver Input Protection Scheme

TRANSMITTER

OUTPUT

Figure 31. Transmitter Output Protection Scheme

The ADM3307E protection scheme is slightly different (see

Figure 32 and Figure 33). The receiver inputs, transmitter

inputs, and transmitter outputs contain two back-to-back high

speed clamping diodes. The receiver outputs (CMOS outputs),

the SD and EN pins, contain a single reverse biased high speed

clamping diode. Under normal operation with maximum

CMOS signal levels, the receiver output, SD, and EN protection

diodes have no effect because they are reversed biased. If,

however, the voltage exceeds about 15 V, reverse breakdown

occurs and the voltage is clamped at this level. If the voltage

reaches −0.7 V, the diode is forward biased and the voltage is

clamped at this level. 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.

RIN

RECEIVER

INPUT

RECEIVER

OUTPUT

Figure 32. ADM3307E Receiver Input Protection Scheme

TRANSMITTER

OUTPUT

TRANSMITTER

INPUT

Figure 33. ADM3307E Transmitter Output Protection Scheme

The protection structures achieve ESD protection up to ±15 kV

on all RS-232 I/O lines (and all CMOS lines, including SD and

EN for the ADM3307E). For methods used to test the

protection scheme, see the ESD Testing (IEC 1000-4-2) section.

ESD TESTING (IEC 1000-4-2)

IEC 1000-4-2 (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. Airgap discharge uses a higher test voltage but

does not make direct contact with the unit under testing. With

air discharge, the discharge gun is moved toward the unit under

testing, which develops an arc across the air gap, thus 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

destruction can occur immediately as a result of arcing or

heating. Even if catastrophic failure does not occur immediately,

the device can suffer from parametric degradation that can

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

discharge that can damage or completely destroy the interface

product connected to the I/O port. Traditional ESD test

methods, such as the MIL-STD-883B method 3015.7, do not

fully test a product’s susceptibility to this type of discharge. This

test was intended to test a product’s susceptibility to ESD

damage during handling.

Each pin is tested with respect to all other pins. There are some

important differences between the traditional test and the IEC

test.

• The IEC test is much more stringent in terms of discharge

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

• The current rise time is significantly faster in the IEC test.

• 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

normally with power applied. For maximum peace of mind,

however, both tests should be performed, ensuring maximum

protection both during handling and later during field service.

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