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Gate drivers promise long-term motor control reliability

Posted: 14 May 2013 ?? ?Print Version ?Bookmark and Share

Keywords:gate driver? opto-driver? CMOS? power MOSFET?

Silicon Labs has rolled out what it says is the industry's first digital CMOS-based drop-in replacement solution for optocoupler-isolated gate drivers (opto-drivers). The company said the CMOS-based Si826x supports up to 5kV isolation ratings and up to 10kV surge protection, and offers an ideal configuration, package and footprint for various 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 inferior 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 ageing 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' proven digital isolation technology, the Si826x family is a pin- and footprint-compatible functional upgrade solution for commonly used opto-driver products, indicated the company. 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, noted Silicon Labs. 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 (25ns), 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, stated the firm. The devices also provide superior noise immunity, enabling robust, glitch-free long-term performance in harsh, noisy environments such as industrial motor control. Unlike opto-drivers, isolated gate drivers offer stable performance over time and temperature with no drift. Because of these advantages, the Si826x family provides longer service life and significantly higher reliability than opto-drivers.

The Si826x gate drivers are geared for driving power MOSFETs and insulated gate bipolar transistors (IGBTs) used in motor control and power inverter applications. Supporting gate drive voltages of up to 30V and peak output current ranging from 0.6-4A, the Si826x devices claim to provide best-in-class drive strength for MOSFET and IGBT applications, ensuring fast turn-off and turn-on of external switching transistors for maximum efficiency.

Samples and production quantities of the Si826x isolated gate drivers are available in four package options: SOIC-8 (3.75 kV isolation rating), GW DIP-8 (3.75 kV isolation rating), SO-6 (5 kV isolation rating) and LGA-8 (5 kV isolation rating). Because these package types are pin- and footprint-compatible with popular opto-driver packages, there is no need to change existing designs or PCB layouts to make the easy drop-in switch to isolated gate drivers. The Si8261Ax device has an output current drive capability of 0.6A while the Si8261Bx is capable of driving up to 4A. The Si8261xAx device has an output under-voltage lockout (UVLO) of 5V while the Si8261xBx has an 8V UVLO and the Si8261xCx has a 12V UVLO option.

Si826x family pricing in 10,000-unit quantities begins at $0.71. To help developers evaluate the performance of the Si826x family, Silicon Labs offers the Si826xDIP8-KIT evaluation kit, available for $29.

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