Texas Instruments ISO7421ED

Overview

ISO7421ED from Texas Instruments is a dual-channel digital isolator with channel-direction asymmetry (input→output and output→input), 2500 VRMS galvanic isolation, 50 Mbps signaling rate, 7 ns typical propagation delay, and operates from 3-V to 5.5-V supplies. It prevents ground-loop noise coupling in industrial fieldbus interfaces such as ProfiBus and servo control systems.

For engineers reviewing the ISO7421ED datasheet, ISO7421ED pinout, ISO7421ED application, or ISO7421ED equivalent, key selection criteria include channel directionality (A→B / B←A), fail-safe default-high output behavior, CMTI >25 kV/μs, and SOIC-8 package compatibility with level-shifting I/O between 3.3-V and 5-V domains.

Technical Context

The ISO7421ED implements two independent SiO₂-based isolation barriers with TTL-compatible input thresholds and push-pull outputs. Its asymmetric channel configuration enables bidirectional signal routing across isolated domains without external logic inversion.

It supports mixed-voltage operation: VCCI and VCCO may be independently set to 3.3 V or 5 V, enabling level translation while maintaining 4242 VPK reinforced isolation per VDE V 0884-10 and UL 1577 certification for 1-minute withstand.

Key Specifications

Pinout & Package

Narrow-body SOIC-8 package (4.90 mm × 3.91 mm), surface-mount, RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-channel digital isolator applications.

Compared with ISO7421DR and ADUM1201BRZ, the ISO7421ED provides the narrowest SOIC-8 footprint (4.9 mm × 3.91 mm) with certified 2500 VRMS isolation and guaranteed default-high output - making it optimal for space-constrained, safety-compliant industrial designs requiring deterministic fail-safe behavior.

Availability

ISO7421ED is available at Aetrix Electronics and suitable for industrial fieldbus, servo control, and isolated power supply monitoring requiring stable component supply and long-lifecycle support.

Supply support for ISO7421ED includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and communications markets.

The ISO742x family was designed specifically for high-reliability galvanic isolation in harsh industrial environments, emphasizing low propagation delay, high CMTI, and fail-safe operation without integrated filters.

FAQ

What is the default output state of the ISO7421ED during input-side power loss?

The ISO7421ED features a default-high output configuration. When VCC1 or input signals are lost, both OUTA and OUTB drive logic-high. This fail-safe behavior ensures predictable system state in industrial controllers - for example, holding a motor enable line active until safe shutdown is commanded. The ISO7421ED does not require external pull-up resistors to achieve this behavior.

Does the ISO7421ED support level translation between 3.3-V and 5-V domains?

Yes, the ISO7421ED supports independent 3.0–5.5-V supplies on VCC1 (input side) and VCC2 (output side). When VCC1 = 3.3 V and VCC2 = 5 V, the ISO7421ED translates 3.3-V logic inputs to 5-V outputs with VOH ≥ 4.6 V and VOL ≤ 0.4 V. Inputs remain 5-V tolerant, allowing direct connection to 5-V sensors without clamping diodes. This capability is confirmed in Sections 6.6 and 6.7 of the ISO7421ED datasheet.

How does the ISO7421ED differ from the ISO7420ED in channel configuration?

The ISO7421ED has asymmetric channel direction: channel A is input→output (INA → OUTA), and channel B is output←input (INB → OUTB, i.e., reverse direction). In contrast, the ISO7420ED has both channels unidirectional input→output (INA → OUTA, INB → OUTB). This makes the ISO7421ED ideal for full-duplex protocols like UART, whereas ISO7420ED suits parallel data or dual unidirectional signals. Pin functions and package are identical.

What safety certifications apply to the ISO7421ED?

The ISO7421ED is certified to UL 1577 (2500 VRMS, 1 minute), VDE V 0884-10 (4242 VPK, reinforced), CSA Component Acceptance Notice 5A, IEC 60950-1, IEC 61010-1, and CQC GB4943.1-2011. These approvals validate its suitability for industrial equipment, medical auxiliary circuits, and energy metering systems requiring reinforced isolation. Certification details are listed in Section 1 of the ISO7421ED datasheet.

Can the ISO7421ED replace optocouplers in existing designs?

Yes, the ISO7421ED is explicitly positioned as an optocoupler replacement in industrial fieldbus, ProfiBus, ModBus, DeviceNet™, servo control, motor control, power supplies, and battery packs. Its 50 Mbps speed, 7 ns propagation delay, and 25–50 kV/μs CMTI exceed typical optocoupler performance. Unlike optocouplers, the ISO7421ED offers stable timing over temperature and lifetime, no LED aging, and guaranteed default-high output - all verified in TI's ISO7421ED application notes and test reports.