Part Number: ADM2491E

Manufacturer: Analog Devices Inc

Description: ADI Isolator RS-485 Transceiver IC

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Technical Specifications of ADM2491EBRWZ

Datasheet  ADM2491EBRWZ datasheet
Category Isolators
Family Digital Isolators
Manufacturer Analog Devices Inc.
Series iCoupler?
Packaging Tube
Part Status Active
Technology Magnetic Coupling
Type RS422, RS485
Isolated Power No
Number of Channels 3
Inputs – Side 1/Side 2 2/1
Channel Type Unidirectional
Voltage – Isolation 5000Vrms
Common Mode Transient Immunity (Min) 25kV/μs
Data Rate 16Mbps
Propagation Delay tpLH / tpHL (Max) 60ns, 60ns
Pulse Width Distortion (Max)
Rise / Fall Time (Typ) 20ns, 20ns (Max)
Voltage – Supply 3.3V, 5V
Operating Temperature -40°C ~ 85°C
Package / Case 16-SOIC (0.295″, 7.50mm Width)
Supplier Device Package 16-SOIC

The ADM2491E is a high-speed, half- or full-duplex data transceiver for multipoint transmission lines; it is isolated and protected from ESD up to 8 kilovolts. The transmission line is shared between the transmitter and receiver in a half-duplex configuration. From the outside, you’ll notice that the transmitter’s Pin Y is connected to Pin A, and the transmitter’s Pin Z is connected to Pin B, both of which belong to the receiver. The ADM2491E follows the ANSI TIA/EIA RS-485-A-1998 and the ISO 8482: 1987 standards for balanced transmission lines.

Incorporating the iCoupler® technology developed by Analog Devices, Inc., this device integrates a 3-channel isolator, a 3-state differential line driver, and a differential input receiver into a single housing. Electrostatic discharge circuitry shielding 8 kV using a human body as a model (HBM) is built into the differential transmitter and receiver inputs . The device’s logic side can be powered by either a 5 V or 3.3 V source, but the bus side must have its own dedicated 5 V source. The device is protected from output short circuits and overheating due to bus contention with its current-limiting and thermal shutdown capabilities. The ADM2491E is a broad body, 16-lead SOIC device that can function between 40°C and +85°C.

ADM2491E Features

  • It has  ±8 kV ESD protection
  • The logic side of the device can be powered with either a 5 V or a 3.3 V supply
  • It has current-limiting and thermal shutdown to protect against output short circuits
  • It operates over the −40°C to +85°C temperature range.
  • is suitable for high speed, half- or full-duplex communication on multipoint transmission lines
  • It has current-limiting and thermal shutdown to protect against output short circuits
  • It is Designed for balanced transmission

More Features and Applications

PCB Layout

There is no need for any external interface circuitry for the logic interfaces when using the ADM2491E isolated RS-485 transceiver. Implementing power supply bypassing at the input and output supply pins is necessary. It is convenient to attach bypass capacitors between Pin 1 and 2 for VDD1 and between Pin 15 and 16 for VDD2. The value of the capacitor ought to be somewhere in the range of 0.01 to 0.1 microfarads. Overall lead length, including capacitor ends and input power supply pin, must not exceed the limit 20 mm. Bypassing should also be considered between Pin number 1, 8,9 and also 16 unless each side’s ground pair is linked near the package.

Circuit Description Electrical Isolation

On the logic side of the interface found in the ADM2491E, electrical isolation is a feature that has been implemented. Because of this, the component is divided into two primary parts: a segment for digital isolation and a section for the transceiver . The driver input signal is connected through an isolation barrier to appear at the transceiver section referred to as isolated ground.

This signal is applied to the TxD pin and referenced to logic ground (GND1) (GND2). Similarly, the receiver input, referenced to isolated ground in the transceiver portion, is linked across the isolation barrier. It appears at the RxD pin, which is referenced to logic ground.

iCoupler Technology

With the help of iCoupler technology, digital signals can be carried across the isolation barrier. Using this approach, which employs chip-scale transformer windings, the digital signals are magnetically connected from one side of the barrier. Encoded with the received digital inputs are the waveforms capable of triggering the primary transformer winding. At the secondary part of winding, the induced type of waveforms are decoded to determine the transmitted original binary value.

Thermal Shutdown

The ADM2491E incorporates thermal shutdown circuitry, which prevents the component from losing an excessive amount of power in the event of a malfunction. High driver currents can accidentally connect the driver outputs to a source with a low impedance. Under these circumstances, the thermal sensing circuitry recognizes an increase in die temperature and turns off the driver outputs. When a temperature of 150 degrees Celsius is reached on the die, this circuitry is intended to turn off the driver outputs.

Once the temperature drops below 140 degrees Celsius, the drivers can function normally again. FAIL-SAFE RECEIVER INPUTS The receiver inputs come equipped with a fail-safe feature that ensures the presence of a logic high on the RxD pin, even if the A and B inputs are floating or open-circuited.

Fail-Safe Receiver Inputs

When the A and B inputs are floating or open circuits, the receiver inputs include a fail-safe mechanism that assures a logic high on the RxD pin. This feature may be found on the receiver.

Magnetic Field Immunity

Since iCoupler products use coreless type of technology, there are no magnetic components in these devices; hence, the issue of magnetic saturation of the core material is not an issue. As a result, iCoupler devices have an almost unlimited immunity to dc fields. The following analysis will identify the circumstances under which anything like this may occur. The 3 V operating condition of the ADM2491E is investigated because it is the mode of operation that is the most prone to error. The limitation within magnetic ac field of iCoupler is determined by the induced condition large enough voltage error in the bottom coil (receiving coil) to either reset or falsely set the decoder. This condition sets the upper limit on the ac magnetic field immunity.


If you need high-speed, half-, or full-duplex communication over several transmission lines, look no farther than the ADM2491E, an isolated data transceiver with 8 kilovolts of electrostatic discharge (ESD) protection. In a half-duplex setup, the transmission line is used by both the transmitter and receiver. The ADM2491E is built for balanced transmission lines and conforms to ANSI TIA/EIA RS-485-A-1998 and ISO 8482: 1987. Pin Y of the transmitter is connected to Pin A of the receiver, and Pin Z of the transmitter is connected to Pin B of the receiver (E). We hope that this article has provided you with a clear understanding of what the above-mentioned device is and how it functions.

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