SI8640BB-B-ISR Isolators

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Digital isolators are devices used as a means to electrically isolate two circuits using digital signals, usually signaled using logic levels. In this article, we discuss the SI8640BB-B-ISR application field and working principle in the context of this technology.

Application Field of SI8640BB-B-ISR

The SI8640BB-B-ISR utilizes galvanic isolation, achieving 3KV isolation voltage. The device features wide signal range up to 62 MHz and a data rate up to 50 Mbps, which makes it a suitable for applications where the device is needed to transfer high-speed data accurately without the effects of ground loops and changes in the supply voltage. It is suitable for applications such as securing interfaces, protecting data lines from transients and generating system timing signals.

Applications for the SI8640BB-B-ISR include industrial automation and networking systems, automotive networks, smart grid systems, factory automation, medical device isolation and general purpose buffering. Additional applications include the buffering and redriving of LVDS/RS422/RS485 data as well as providing electrical isolation between sensor-actuator interfaces.

Working Principle

Digital isolators are ideal substitutions for physical isolation and use the phenomenon of capacitive coupling to achieve this isolation. The internally included circuit, termed a ‘coupled capacitor’ acts as a low-pass filter, allowing fundamental signals to pass and blocking out-of-band higher order signals. The coupled capacitor is a capacitor created by common-mode voltages of two independent circuits sharing a common ground, thereby creating a capacitive connection across the circuits.

In the case of the SI8640BB-B-ISR, the capacitive coupling of the coupled capacitor is further improved by the secondary side receiver circuitry. It utilizes a gate-biased device, which allows for the input signal to drive the input transistor and thus improving the coupling range of the device. Additionally, the device features an in-built signal grade differential amplifier with low externalized component count. This allows the device to detect and distinguish between low-level signals, improving the detectability due to the significant drop in the threshold voltage.

Limitations

Digital isolators are a great substitute for physical isolation, however, they also come with certain limitations. The most prominent limitation lies in the maximum data rate, specified for a device. The data rate is not only limited by the theoretical bandwidth of the isolator device but also by the amount of noise or jitter that the device can handle. Furthermore, Digital Isolators can also add additional latency to the transmission of data. This is because the capacitance needed to create the isolation barrier adds some additional delay to the data signal.

Conclusion

The SI8640BB-B-ISR is a digital isolator that utilizes galvanic isolation and capacitive coupling for 3KV of isolation voltage. It is suitable for applications such as industrial automation, automotive networks, smart grid systems, factory automation, medical device isolation and general purpose buffering. The working principle of the device involves the utilization of a coupled capacitor and a gate-biased device to improve its coupling range and detectability. However, there are several limitations with Digital Isolators such as maximum data rate and latency.

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