ADM2461EBRWZ-R7 datasheet(19/21 Pages) AD

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Data Sheet

ADM2461E/ADM2463E

Rev. 0 | Page 19 of 21

APPLICATIONS INFORMATION

PCB LAYOUT AND ELECTROMAGNETIC

INTERFERENCE (EMI)

The ADM2461E/ADM2463E use a low power, on or off keying

encoding scheme for robust communication with minimal

radiated emissions. These devices can meet EN55032 and CISPR

32 Class B requirements with margin on a standard 2-layer PCB,

without the need for complex and area intensive layout techniques.

MAXIMUM DATA RATE vs. AMBIENT

TEMPERATURE

Under a large current load, power dissipation within the

transceiver can limit the maximum ambient temperature

achievable while retaining a silicon junction temperature

below 150°C. This internal power dissipation is related to

application conditions including supply voltage configuration,

switching frequency, effective load on the RS-485 bus, and the

amount of time the transceiver is in transmit mode. Thermal

performance also depends on the PCB design and thermal

characteristics of a system.

For high temperature applications above 85°C with a fully

loaded RS-485 bus (equivalent to 54 Ω bus resistance) operating

with a VDD2 supply of 5 V ± 10%, limiting the transmitter data

rate to 300 kbps is recommended. The thermal resistance (θJA)

of the package can be used in conjunction with the typical

performance curves for the VDD2 supply current to calculate the

maximum data rate for a given ambient temperature.

ISOLATED PROFIBUS SOLUTION

The ADM2461E features a transceiver that meets the

requirements of an isolated Profibus node. When operating the

ADM2461E as a Profibus transceiver, ensure that the VDD2

power supply is a minimum of 4.5 V. The ADM2461E is

acceptable for use in Profibus applications as a result of the

following characteristics:



The output driver meets or exceeds the Profibus differential

output requirements. To ensure that the transmitter

differential output does not exceed 7 V p-p over all

conditions, place 10 Ω resistors in series with the A and

B transmitter outputs.



Low bus pin capacitance of 28 pF.



Class I (no loss of data) immunity to IEC61000-4-4 electrical

fast transients (EFTs) up to ±1 kV with respect to the GND2

pin can be achieved using a Profibus shielded cable. IEC

61000-4-4 Class I up to ±3 kV can be achieved with the

addition of a 470 pF capacitor connected between the

GND1 pin and the RxD output pin.

EMC, EFT, AND SURGE PROTECTION

In applications where additional levels of protection against

IEC61000-4-5 EFT or IEC61000-4-4 surge events are required,

external protection circuits can be added to enhance the EMC

robustness of the device. See Figure 43 for a recommended EMC

protection circuit that uses a series of SM712 transient voltage

suppressors (TVS) and 10 Ω pulse proof resistors to achieve

Level 2 IEC61000-4-5 surge protection and an excess of Level 4

IEC61000-4-2 ESD and IEC61000-4-4 EFT protection. Table 16

and Table 17 list the recommended protection components and

protection levels for this circuit.

VDD1

RxD

RECEIVER

TxD

DRIVER

SM712

TVS

SM712

TVS

10Ω

GND1

GND2

ISOLATION

BARRIER

10Ω

120Ω

VDD2

Figure 43. Isolated RS-485 Solution with ESD, EFT, and Surge Protection

Table 16. Recommended Components for ESD, EFT, and

Surge Protection Solution

Recommended Components

Part Number

TVS

CDSOT23-SM712

10 Ω Pulse Proof Resistors

CRCW060310R0FKEAHP

Table 17. Protection Levels with Recommend Circuit

EMC Standard

Protection Level (kV)

ESD—Contact (IEC 61000-4-2)

≥ ±30 (exceeds Level 4)

ESD—Air (IEC 61000-4-2)

≥ ±30 (exceeds Level 4)

EFT (IEC 61000-4-4)

≥ ±4 (exceeds Level 4)

Surge (IEC 61000-4-5)

≥ ±1 (Level 2)

INSULATION LIFETIME

All insulation structures eventually break down when subjected

to voltage stress over a sufficiently long period of time. The rate

of insulation degradation depends on the characteristics of the

voltage waveform applied across the insulation and on the

materials and material interfaces.

The two types of insulation degradation of primary interest are

breakdown along surfaces exposed to the air and insulation wear

out. Surface breakdown is the phenomenon of surface tracking

and is the primary determinant of surface creepage requirements

in system level standards. Insulation wear out is the phenomenon

where charge injection or displacement currents inside the

insulation material cause long-term insulation degradation.

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