Part Number: ADM2582EBRWZ-REEL7

Manufacturer: Analog Devices

Description: Digital Isolators ISOLATED RS485 HD/FD 16Mbps IC

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ADM2582EBRWZ-REEL7 General Description

Technical Specifications of ADM2582EBRWZ-REEL7

Datasheet  ADM2582EBRWZ-REEL7 datasheet
Category Isolators
Family Digital Isolators
Manufacturer Analog Devices Inc.
Series IsoPower?, iCoupler?
Packaging Tape & Reel (TR)
Part Status Active
Technology Magnetic Coupling
Type RS422, RS485
Isolated Power Yes
Number of Channels 3
Inputs – Side 1/Side 2 2/1
Channel Type Unidirectional
Voltage – Isolation 2500Vrms
Common Mode Transient Immunity (Min) 25kV/μs
Data Rate 16Mbps
Propagation Delay tpLH / tpHL (Max)
Pulse Width Distortion (Max)
Rise / Fall Time (Typ) 15ns, 15ns (Max)
Voltage – Supply 3.3V, 5V
Operating Temperature -40°C ~ 85°C
Package / Case 20-SOIC (0.295″, 7.50mm Width)
Supplier Device Package 20-SOIC

Compatible with high-speed communication via various multipoint transmission lines, the ADM2582E and ADM2587E are completely integrated, power- and signal-separated data transceivers with up to 15 kV of ESD protection. Because of the isolated dc-to-dc power supply included in the ADM2582E/ADM2587E, a separate dc-to-dc isolation block is not required. They meet the requirements of ANSI/TIA/EIA-485-A-98 and ISO 8482:1987; therefore, they can be used with balanced transmission lines (E).

These devices combine a three-channel isolator, a three-state differential line driver, an Analog DevicesisoPower® dc-to-dc converter and a differential input receiver nto a single package using iCoupler® technology. A complete signal and isolated RS-485 solution are achieved by powering the devices with a single 5 V or 3.3 V supply. There is an active high enable on the ADM2582E/ADM2587E driver. The receiver’s output goes into a high-impedance condition when the active low receiver enables is turned on. The devices incorporate current limiting and thermal shutdown functions to prevent damage in the event of an output short circuit or when bus contention could lead to excessive power dissipation.

These components come in a 20-lead, wide-body SOIC package and are fully specified for use in an industrial temperature range. To transfer energy via the transformer, the ADM2582E/ADM2587E uses isoPower technology, which uses high-frequency switching elements. The layout of a printed circuit board (PCB) requires extra attention to ensure it complies with regulations regarding emissions.

Circuit Description

Signal Isolation

Interface logic is where you’ll find the signal separation for the ADM2582E/ADM2587E. A digital isolation section and a transceiver section in the component work together to block incoming signals.

By connecting the TxD and DE pins to logic ground (GND1), data can be transmitted to the transceiver portion, which is grounded independently (GND2). The RXD pin, connected to the logic ground, receives the single-ended receiver output signal from the transceiver portion through coupling across the isolation barrier.

Power Isolation

An isoPower-integrated isolated dc-to-dc converter provides power isolation for the ADM2582E/ADM2587E. The ADM2582E/dc-to-dc ADM2587E converter operates according to the same principles as other current power supplies. It’s a feedback-free pulse-width modulation (PWM) design for a secondary controller. A microchip-sized air core transformer receives current via an oscillating circuit powered by the supply voltage. The voltage of the secondary side’s transferred power is regulated at 3.3 V after rectifying. The controller on the secondary (VISO) side generates a PWM control signal, then transmitted to the controller on the primary (VCC) side through a separate iCoupler data channel to regulate the output. Control of the secondary side’s power is achieved using PWM modulation of the oscillator circuit. The use of feedback allows for greatly increased output and performance.

Thermal Shutdown

The thermal shutdown circuitry found in the ADM2582E and ADM2587E protects the components from the excessive loss of power that can occur in the event of a malfunction. High driver currents can be produced if the outputs of the driver are connected directly to a source with a low impedance. Under these circumstances, the thermal sensor circuitry can detect an increase in the die temperature and, in response, disables the driver outputs. When the die reaches 150 degrees Celsius, this circuitry is programmed to turn off the driver outputs. At a temperature of 140 degrees Celsius, the drivers are enabled again while the device cools down.

Open- And Short-Circuit Inputs

The receiver inputs have fail-safe features known as open- and short-circuit protection, which ensures that the receiver output remains high even when the inputs are either open or shorted. The voltage across a termination resistance at the receiver input gradually drops until it reaches 0 V when the line is idle, and no driver on the bus is activated. Traditional transceivers have receiver input thresholds set between 200 mV and +200 mV.

External bias resistors are needed on the A and B pins to assure receiver outputs. The short-circuit, fail-safe receiver input function avoids the requirement for bias resistors by choosing the receiver input threshold between -30 mV and -200 mV. This range allows the receiver input to be safe during a short circuit. When A and B reach 0 V, the receiver output is high due to the assured negative threshold because the threshold is always negative.

DC Correctness and Magnetic Field Immunity

iCoupler technology allows digital signals to travel over an isolation barrier. This method employs transformer windings on the scale of a single chip to magnetically link digital signals from one side of a barrier to the other. The primary transformer winding can be excited by waveforms encoded from digital inputs. The induced waveforms are converted into the transmitted binary value at the secondary winding. The decoder receives brief pulses (1 ns) from the transformer whenever there is a positive or negative logic transition at the isolator input.

Because it is bistable, the decoder can be set or reset by pulses representing logic transitions at the input. If there is a delay of more than 1 s between logic changes at the input, the output will be made dc correct by sending periodic groups of refresh pulses that correspond to the proper input state. If the decoder doesn’t get any internal pulses for more than 5 s, the input side is considered unpowered or not working. In this case, the watchdog timer circuit sets the isolator’s output to a default state.

The ADM2582E/ADM2587E devices should only experience this issue during power-on and power-off procedures. When the induced voltage in the transformer’s receiving coil is high enough to set or reset the decoder incorrectly, the ADM2582E/ADM2587E are no longer immune to magnetic fields of that strength. In this analysis, we will identify the parameters within which this is possible. Due to the high susceptibility of the ADM2582E/ADM2587E in this operating situation, we focus on the 3.3 V operating condition, where the pulses at the transformer output have an amplitude of >1.0 V. Given that the decoder’s sensing threshold is at 0.5 V, this creates a tolerance range for induced voltages of up to 0.5 V.


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