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I2C helps controllers communicate with sensors, data converters, and other nearby integrated circuits (ICs). Isolated I2C-compatible signal isolators like TI’s ISO1640 and ISO1641 create opportunities for the protocol to be used in systems that are physically distant, operating at different local voltage potentials, and require isolation protection for operation or safety.
Sensitive systems or those in need of protection from large DC and AC currents, ground-potential differences, and high-voltage events can be protected by TI’s digital isolators when used with isolated power supplies. Although most digital isolation devices isolate signals in one direction for communication across an isolation barrier, TI’s bidirectional signal isolators isolate bidirectional signals for I2C. They accomplish this by combining two unidirectional signal paths internally, as Figure 1-1 shows, across the industry’s strongest silicon dioxide (SiO2) isolation barrier.
Bidirectional communication is inherent to I2C, and using an isolator with integrated bidirectional lines provides the benefits of: a low discrete component count, small footprint, less system-wide variations, and built-in protection over discrete solutions.
Hot swap is the replacement or addition of components to a powered system without pausing, powering down, or restarting the system and maintaining normal operation. Preserving normal operation of an I2C bus includes not affecting communication by loading the bus or corrupting an ongoing bitstream. When an I2C node or device is first connected to a system, there is no power supply holding the gates of the internal I2C output FETs to ground, and if the power-up transient on the drain of these pins is fast enough, it may couple to the gate of these output FETs, lifting the gate voltage enough to turn the switch ON momentarily. This, in turn, could reduce bus voltage levels enough to cross the HIGH/LOW thresholds of different devices, resulting in communication errors or data corruption across the bus.
Hot-swapping capabilities help preserve the communication integrity of an I2C bus when replacing nodes or devices, making them most beneficial to high-reliability or zero down-time systems that must be maintained or upgraded while operating. Hot-swappable parts must protect sensitive components against electrical shocks, so using components that are not designed to be hot-swapped or that are partially hot-swappable instead of fully hot-swappable could result in instant errors and possibly hardware failure or damage. To preserve communication during hot-swap events in a system with multiple removable nodes or modules, each removable node must have the ability to be withdrawn and replaced without affecting the operation of any adjacent nodes, regardless of power supply levels and bus activity.
Digital signal isolation protects low voltage, logic-level subsystems from mid-to-high-voltage sensors, actuators, and transient events. In systems with long cables or in noisy environments, high voltage transients can occur and damage low-voltage circuitry. I2C-compatiable digital isolators, like ISO1640 and ISO1641, help protect low-voltage circuitry from high voltages, and their hot-swap capability combines bus dependability when adding or removing I2C nodes with isolation protection from undesired or unexpected voltage shifts.
By design, ISO1640 and ISO1641 isolated I2C devices have full “hot-swap” compliance and can help prevent the common modes of failure from using regular I2C devices without the following hot-swap feature:
Examples of how TI’s fully hot-swappable I2C devices outperform other devices to prevent some of the modes of failure listed above are demonstrated in the following section.