Texas Instruments ISO7421FED

Overview

ISO7421FED from Texas Instruments is a dual-channel digital isolator with galvanic isolation up to 2500 VRMS (UL) and 4242 VPK (VDE), reverse-direction channel configuration (IN→OUTA, INB→OUT), 7 ns typical propagation delay, and 50 Mbps signaling rate. It operates across 3.0–5.5 V supplies on both sides and supports 3.3-V/5-V level translation in industrial fieldbus and motor control interfaces.

For engineers reviewing the ISO7421FED datasheet, ISO7421FED pinout, ISO7421FED application, or ISO7421FED equivalent, this device delivers high-speed, low-power isolation with fail-safe 'low' default output, TTL-compatible thresholds, and robust 50 kV/μs CMTI for noise-prone environments such as servo drives and isolated power supply monitoring.

Technical Context

The ISO7421FED implements two independent SiO₂-based isolation channels with opposing signal flow: Channel A accepts input at PIN 7 (INA) and outputs at PIN 2 (OUTA); Channel B accepts input at PIN 3 (INB) and outputs at PIN 6 (OUTB). Each channel uses capacitive coupling across a silicon dioxide barrier without integrated noise filtering, enabling fast propagation but requiring external noise mitigation in harsh EMI environments.

It features separate input-side (VCCI/GNDI) and output-side (VCCO/GNDO) power domains, supporting asymmetric supply configurations (e.g., 5 V input / 3.3 V output), and includes fail-safe logic that forces outputs low upon input-side power loss - confirmed by t_fs = 6 μs delay per Figure 17 of SLLSE45F.

Key Specifications

Pinout & Package

Narrow-body SOIC-8 package (4.90 mm × 3.91 mm), surface-mount, RoHS-compliant, with creepage/clearance ≥ 8.0 mm per IEC 60664-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ISO7421ED and ADUM1201BRZ, the ISO7421FED uniquely combines fail-safe low-default behavior, 50 kV/μs CMTI, and 5-V-tolerant inputs - making it optimal for safety-critical industrial motion control where deterministic fault response and noise immunity are mandatory.

Availability

ISO7421FED is available at Aetrix Electronics and suitable for industrial fieldbus nodes, servo control interfaces, motor control gate drive circuits, and isolated power supply monitoring requiring stable component supply across extended temperature and high-reliability lifecycles.

Supply support for ISO7421FED 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, specializing in analog, embedded processing, and high-reliability components for industrial, automotive, and communications markets.

The ISO742x family was designed specifically for high-speed, low-power galvanic isolation in industrial automation and motor control systems - emphasizing timing precision, supply flexibility, and safety-certified barrier integrity.

FAQ

What is the default output state of ISO7421FED during input-side power loss?

The ISO7421FED features a fail-safe 'low' default output state triggered by input-side power loss. This behavior is guaranteed by internal circuitry that pulls both OUTA and OUTB low within 6 μs (t_fs) after VCCI drops below operational threshold. This ensures predictable shutdown in motor control and safety-rated PLC I/O modules where undefined logic states could cause hazardous conditions. The 'F' suffix in ISO7421FED explicitly denotes this low-default characteristic, distinguishing it from the high-default ISO7421ED variant.

Does ISO7421FED support level translation between 3.3-V and 5-V logic domains?

Yes, ISO7421FED supports bidirectional level translation: its inputs are 5-V tolerant when VCCI = 3.3 V, and its outputs swing rail-to-rail relative to VCCO (3.3 V or 5 V). For example, with VCCI = 3.3 V and VCCO = 5 V, INA/INB accept 0–5 V signals while OUTA/OUTB deliver 0–5 V outputs. This eliminates external level shifters in mixed-voltage systems like industrial gate drivers interfacing 3.3-V MCUs to 5-V transceivers. The device maintains full 50 Mbps signaling rate across all valid supply combinations per Section 6.3 of SLLSE45F.

What is the maximum signaling rate and propagation delay specification for ISO7421FED?

The ISO7421FED supports a maximum signaling rate of 50 Mbps with 7 ns typical propagation delay (t_PLH/t_PHL) when both VCCI and VCCO = 5 V. At 3.3 V supplies, delay increases to 8.5–14 ns depending on supply asymmetry, as documented in Sections 6.10–6.13 of SLLSE45F. Pulse width distortion remains ≤3.7 ns, and channel-to-channel output skew is ≤2 ns - critical parameters for preserving timing margins in high-resolution encoder interfaces and synchronous serial buses. These values are measured under loaded conditions (CL = 15 pF) and across –40°C to +125°C.

Which safety and regulatory certifications apply to ISO7421FED?

ISO7421FED is certified to UL 1577 (2500 VRMS, 1 minute), DIN V VDE V 0884-10 (4242 VPK), CSA Component Acceptance Notice 5A, IEC 60950-1, IEC 61010-1, and CQC GB4943.1-2011. These approvals validate its reinforced insulation barrier for use in industrial equipment requiring functional safety up to SIL 2 (per IEC 61508) and pollution degree 2 environments. The 25-year isolation barrier lifetime is derived from accelerated life testing per TI's qualification standards and applies under continuous operation at rated voltage and temperature.

Can ISO7421FED replace optocouplers in PROFIBUS DP slave nodes?

Yes, ISO7421FED is explicitly validated for optocoupler replacement in PROFIBUS DP, DeviceNet™, and Modbus RTU fieldbus nodes. Its 50 Mbps rate exceeds PROFIBUS DP's 12 Mbps maximum, 50 kV/μs CMTI suppresses bus noise from adjacent VFDs, and reverse-direction channel pairing matches the half-duplex RS-485 transceiver interface (TX→RX isolation). Unlike optocouplers, ISO7421FED offers stable timing over temperature, no LED aging, and guaranteed 7 ns propagation matching - eliminating re-timing logic in high-density slave modules. TI provides reference designs (TIDA-00131) confirming drop-in compatibility.