Digital isolation replaces opto devices for reliable motor controls

May 09, 2013 // By Graham Prophet
CMOS-based isolated gate drivers provide robust drop-in replacements for opto-drivers used in industrial power systems.

Silicon Labs has introduced the first digital CMOS-based drop-in replacement solution for optocoupler-isolated gate drivers (opto-drivers). Supporting up to 5 kV isolation ratings and up to 10 kV surge protection, the Si826x isolated gate drivers provide a configuration, package and footprint fit for a wide range of opto-drivers used in high-power motor control, industrial drives, solar power and EV/HEV inverters, and switched mode and uninterruptible power supplies.

Failure-prone opto-drivers are a weak link in motor controls and other industrial power systems that require long-term reliability, extended warranties and fail-safe operation for up to 20 years. Opto-drivers are inherently limited by their LED-based technology, which is subject to large output variations over input current, temperature and age. These variations are eliminated by using Si826x isolated gate drivers. Less variability, especially in input turn-on current, simplifies system design since developers no longer need to anticipate aging effects. Higher reliability and longer device lifetime also allow system manufacturers to support longer warranties and reduce costs associated with product repair or replacement.

Based on Silicon Labs’ digital isolation technology, the Si826x family is a pin- and footprint-compatible functional upgrade solution for commonly used opto-driver products. Si826x isolated gate drivers emulate the behaviour of opto-drivers by modulating a high-frequency carrier instead of light from an LED. This simpler digital architecture provides a robust isolated data path that requires no special considerations or initialisation at start-up. While the input circuit mimics the characteristics of an LED, the Si826x devices require less drive current, resulting in higher efficiency. The propagation delay time of Si826x devices is independent of the input drive current, resulting in consistently short propagation times (25 nsec), smaller unit-to-unit variation and greater input circuit design flexibility.

The propagation delay and skew of Si826x isolated gate drivers is ten-times lower than opto-drivers, which improves response time for feedback loops and enhances system efficiency. The Si826x devices also provide superior noise immunity, enabling robust glitch-free long-term