ADM3095E

Data Sheet

Rev. C | Page 12 of 19

Miswiring protection is guaranteed on the ADM3095E RS-485

bus A and B pins and during a hot swap of connectors to the bus

pins. Table 6 provides a summary of the high voltage miswire

protection offered by the ADM3095E. The ADM3095E is tested

with ±42 V dc and to ±24 V ±20% rms, 50 Hz or 60 Hz with

both a hot plug and dc ramp test waveforms. The test is

performed in both powered and unpowered power supply cases

and at a range of different states for the RS-485 TxD input and

DE/RE enable pins. The RS-485 bus pins survive a high voltage

miswire from Pin A to GND, from Pin B to GND, and between

Pin A and Pin B.

Table 6. High Voltage Miswire Protection

Supply1

Inputs2

Miswire Protection at

RS-485 Output Pins3, 4

VCC

VIO

DE

RE

TxD

X

X

H/L

H/L

H/L

−42 V dc ≤ VA ≤ +42 V dc

X

X

H/L

H/L

H/L

−42 V dc ≤ VB ≤ +42 V dc

X

X

H/L

H/L

H/L

−42 V ac ≤ VA ≤ +42 V ac

X

X

H/L

H/L

H/L

−42 V ac ≤ VB ≤ +42 V ac

1

X means on or off power supply state.

2

H means high level for the logic pin; L means low level for the logic pin.

3

This is the ac/dc peak miswire voltage between Pin A and GND, Pin B and

GND, or between Pin A and Pin B.

4

VA refers to the voltage on Pin A and VB refers to the voltage on Pin B.

RS-485 NETWORK BIASING AND TERMINATION

For a high voltage miswire on the RS-485 A and B bus pins with

biasing and termination resistors installed, there is a current

path through the biasing network to the ADM3095E power

supply VCC pin. To protect the ADM3095E for this scenario the

device has an integrated VCC protection circuit, meaning the

current path through the R1 pull-up resistor (see Figure 32)

does not cause damage to the VCC pin, although the pull-up

resistor can be damaged if not appropriately power rated. The

R1 pull-up resistor power rating depends on the miswire

voltage and the resistance value.

For the scenario where there is a miswire between the A and B

pins, the ADM3095E bus setup (see Figure 32) is protected, but

the RT bus termination resistor is damaged if not appropriately

power rated. The RT termination resistor power rating depends

on the miswire voltage and the resistance value.

R2

390Ω

RT

220Ω

R1

390Ω

A

B

VCC

R

D

RxD

RE

DE

TxD

A

B

VCC

ADM3095E

EMC

TRANSIENT

PROTECTION

CIRCUIT

GND

GND

VIO

LEVEL

TRANSLATOR

Figure 32. High Voltage Miswiring Protection for the ADM3095E with Bus

Termination and Biasing Resistors

IEC ESD, EFT, AND SURGE PROTECTION

Electrical and electronic equipment must be designed to meet

system level IEC standards. The following are example system

level IEC standards:

•

IEC 61131-2—process control and automation

•

IEC 61800-3—motor control

•

IEC 60730-1—building automation

For data communication lines, these system level standards

specify varying levels of protection against the following three

types of high voltage transients:

•

IEC 61000-4-2 ESD

•

IEC 61000-4-4 EFT

•

IEC 61000-4-5 surge

Each of these specifications defines a test method to assess the

immunity of electronic and electrical equipment against the

defined phenomenon. The following sections summarize each

of these tests. The ADM3095E is fully tested in accordance with

these IEC EMC specifications and is certified EMC compliant.

Electrostatic Discharge (ESD)

ESD is the sudden transfer of electrostatic charge between bodies at

different potentials caused by near contact or induced by an electric

field. ESD has the characteristics of high current in a short time

period. The primary purpose of the IEC 61000-4-2 test is to

determine the immunity of systems to external ESD events outside

the system during operation. IEC 61000-4-2 describes testing using

two coupling methods, known as contact discharge and air gap

discharge.

Contact discharge implies a direct contact between the discharge

gun and the equipment under test (EUT). During air gap discharge

testing, the charged electrode of the discharge gun moves toward

the EUT until a discharge occurs as an arc across the air gap.

The discharge gun does not make direct contact with the EUT.

A number of factors affect the results and repeatability of the air

gap discharge test, including humidity, temperature, barometric

pressure, distance, and rate of approach to the EUT. This method is

a better representation of an actual ESD event but is not as

repeatable. Therefore, contact discharge is the preferred test

method.

During testing, the data port is subjected to at least 10 positive

and 10 negative single discharges with a one second interval

between each pulse. Selection of the test voltage is dependent on

the system end environment.

The ADM3095E is robust to IEC 61000-4-2 events and passes

the highest level recognized in the standard Level 4, which

defines a contact discharge voltage of ±8 kV and an air gap

discharge voltage of ±15 kV.