Skyworks Solutions Inc. SI8421BD-B-ISR

Overview

SI8421BD-B-ISR from Silicon Labs is a dual-channel, 5 kV reinforced digital isolator in SOIC-16 wide-body package, supporting up to 150 Mbps data rate with 8 ns typical propagation delay, <1.5 ns pulse width distortion, and 45 kV/µs common-mode transient immunity. It operates from 2.7–5.5 V supply and is used in isolated gate drivers for motor inverters and isolated ADC interfaces in industrial PLCs.

For engineers reviewing the SI8421BD-B-ISR datasheet, SI8421BD-B-ISR pinout, SI8421BD-B-ISR application, or SI8421BD-B-ISR equivalent, key selection criteria include its 5 kV isolation rating, fail-safe output mode selection, ultra-low power consumption at 100 Mbps (6.8 mA/channel @ 5 V), and compatibility with high-speed SPI, RS-485, and I²C isolation requirements.

Technical Context

The SI8421BD-B-ISR implements capacitive isolation using on-chip RF modulation/demodulation across a silicon dioxide barrier, enabling stable timing performance over –40 to +125 °C. Its dual-channel architecture supports independent bidirectional or unidirectional signal paths with Schmitt-trigger inputs for noise immunity.

It features selectable fail-safe mode (default-high or default-low output during power loss), under-voltage lockout with 2.3 V threshold and 75 mV hysteresis, and precise channel-to-channel skew of ≤0.5 ns - critical for time-sensitive feedback loops in servo drives and isolated current sensing.

Key Specifications

Pinout & Package

SI8421BD-B-ISR is housed in a 16-pin wide-body SOIC package (package width 10.3 mm) with 8.0 mm minimum creepage and clearance, certified for reinforced insulation per IEC 60747-5-2 and UL 1577.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADUM121N1BRZ-RL7 and ISO6721FDWR, SI8421BD-B-ISR uniquely delivers dual-channel 150 Mbps operation with 5 kV reinforced isolation and 6.8 mA/channel power efficiency - making it optimal for next-generation motor drives and isolated ADC interfaces where timing precision and safety compliance are co-critical.

Availability

SI8421BD-B-ISR is available at Aetrix Electronics and suitable for industrial motor drives, medical imaging power supplies, EV onboard chargers, and isolated data acquisition systems requiring stable component supply across extended product lifecycles.

Supply support for SI8421BD-B-ISR 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

Silicon Labs is a fabless semiconductor company specializing in secure, intelligent wireless and wired connectivity solutions for IoT, industrial, and automotive markets.

The Si84xx family was designed specifically for high-reliability galvanic isolation in harsh electromagnetic environments - targeting motor control, power conversion, and medical equipment where safety certification, timing accuracy, and low power at speed are mandatory.

FAQ

What is the maximum data rate supported by the SI8421BD-B-ISR?

The SI8421BD-B-ISR supports a maximum data rate of 150 Mbps under standard operating conditions (VDD = 5 V, TA = –40 to +125 °C, CL = 15 pF). This is confirmed in Table 1 timing characteristics for Si842xBx variants. At lower supply voltages (e.g., 2.7 V), the device maintains full 150 Mbps capability, as verified in Table 3 electrical specs. The SI8421BD-B-ISR achieves this with worst-case propagation delay under 11 ns and pulse width distortion below 3 ns.

Does the SI8421BD-B-ISR support fail-safe operation, and how is it configured?

Yes, the SI8421BD-B-ISR supports selectable fail-safe output mode - default-high or default-low - during power loss or undervoltage conditions. Configuration is determined by the state of the FS pin (Pin 7) at power-up: pulled high for default-high output, pulled low for default-low. This behavior is documented in Section 3.4 "Fail-Safe Operating Mode" and ensures predictable gate driver or ADC interface states during brownout events. The SI8421BD-B-ISR implements this via internal UVLO monitoring with 2.3 V threshold and 75 mV hysteresis.

What safety certifications apply to the SI8421BD-B-ISR?

The SI8421BD-B-ISR carries UL 1577 (5000 VRMS), CSA Component Notice 5A (IEC 60950-1/61010-1/60601-1), and VDE IEC 60747-5-2 certifications. These cover reinforced insulation for working voltages up to 600 VRMS (UL/CSA) and 891 Vpeak (VDE), validated for the SOIC-16 wide-body package. Certification testing includes 6.0 kVRMS for 1 second per production lot, exceeding the rated 5 kVRMS isolation. The SI8421BD-B-ISR is explicitly listed in Tables 6 and 9 of the datasheet as a 5 kV-rated variant.

What is the typical supply current of the SI8421BD-B-ISR at 100 Mbps?

At 100 Mbps, 5 V supply, and 15 pF load, the SI8421BD-B-ISR draws 6.8 mA per channel (13.6 mA total), as specified in Table 1 under "100 Mbps Supply Current" for Si8421Bx variants. At 3.3 V, consumption drops to 5.3 mA/channel. This ultra-low active power enables thermal management in compact motor control modules. The SI8421BD-B-ISR achieves this while maintaining 150 Mbps capability - unlike many isolators that throttle speed to reduce current.

Can the SI8421BD-B-ISR operate with asymmetric supply voltages on each side?

Yes, the SI8421BD-B-ISR supports independent VDD1 and VDD2 supplies ranging from 2.7 V to 5.5 V each, allowing asymmetric configurations such as 3.3 V on the input side and 5 V on the output side. This is explicitly permitted in Table 5 "Recommended Operating Conditions" and enables direct interfacing with mixed-voltage systems - for example, isolating a 3.3 V MCU to a 5 V gate driver IC. The SI8421BD-B-ISR maintains full 150 Mbps performance across all valid VDD combinations.