SI8641AB-B-IS1R

The SI8641AB-B-IS1R is a quad-channel digital isolator from Skyworks Solutions’ Si864x family, providing 3750Vrms isolation using capacitive coupling technology with a silicon-dioxide (SiO2) insulation barrier. The device features three forward and one reverse channel (3/1 configuration) with a default-low output state (B suffix), critical for fail-safe system design. Supporting data rates up to 150Mbps with only 13ns typical propagation delay and 50kV/µs CMTI, it is well-suited for high-speed digital communication across isolation boundaries. The wide supply range of 2.5V to 5.5V on both sides enables voltage-level translation across the barrier. AEC-Q100 qualified, the device is designed for automotive and industrial applications requiring robust isolation in a compact narrow-body SOIC-16 package.

Capacitive Isolation

The Si8641 uses on-chip high-voltage capacitors as the isolation barrier. Input signals are modulated into RF carrier waveforms, transmitted across the capacitive barrier, and demodulated on the receiving side. The differential signaling architecture provides high common-mode noise rejection, enabling the 50kV/µs CMTI specification. Compared to optocouplers, capacitive isolation offers faster speed, lower power, and longer device lifetime without LED degradation.

Differential Signal Transmission

Each channel uses a pair of on-chip capacitors for differential signal transmission. The modulator encodes the input logic state into complementary RF signals that pass through the capacitor pair. On the receive side, the differential signal is demodulated and restored to the original logic level. The differential architecture inherently rejects common-mode noise that appears equally on both capacitors.

Default Output State

The B suffix variant implements a default-low output state. If the input side loses power or the input signal is absent, the output defaults to logic low. This is essential for fail-safe designs where an uncontrolled high output could trigger unintended operation, such as in motor drive or power converter control interfaces.

Level Translation

The independent VDDI and VDDO supply rails allow different voltage levels on each side of the isolation barrier. The input logic thresholds are referenced to VDDI and the output logic levels are referenced to VDDO, enabling seamless translation between 2.5V, 3.3V, and 5V logic domains.

• Automotive CAN bus and motor control isolation requiring AEC-Q100 qualification with fail-safe default-low output
• Industrial SPI and UART communication isolation needing 150Mbps throughput and 50kV/µs CMTI
• Battery management systems where 3750Vrms isolation separates high-voltage battery packs from low-voltage controllers
• Motor drive gate driver interfaces where default-low output prevents accidental gate turn-on during power-up
• Medical device data communication isolation where compact narrow-body SOIC-16 saves board space