Electronic Design

MEMs-Based Magnetic Coils Exceed The Limitation Of Optical Couplers

Implementing surface-micromachined-based magnetic coils in a standard semiconductor process, Analog Devices is readying a new class of ICs for industrial automation, motor control, and data acquisition. MEMS, acting as a post-processed superstructure, has been added to the silicon die to produce the ADuM1100 digital isolator.

This device is designed to provide accurate and fast data-transfer rates in noisy industrial environments. Compared to conventional optical data-transmission methods that employ optocouplers, the isolator substantially improves power consumption and lowers cost. It also uses the magnetic-based approach to digital isolation—or µmIsolation, as ADI calls it—to overcome the inefficiencies associated with electro-optical devices.

The ADuM1100 can support data rates as high as 100 Mbits/s. ADI's business development manager, Ronn Kliger, says that the magnetic coupling technique provides the same level of isolation as optocouplers. Yet it also comes with a threefold improvement in power consumption, propagation delay, pulse-width distortion, and transient immunity.

This isolator comprises a driver that's magnetically coupled to a receiver, which in turn uses a MEMS-based transformer consisting of high-Q micromachined primary and secondary coils. "With 100 nH in inductance, the spiral coils are tightly coupled to achieve high mutual coupling," says Geoff Haigh, senior staff scientist at ADI. "In essence, the design uses two MEMS-based transformers, separated by an insulating layer, to generate a differential signal for the receiver chip."

Other salient features include 2.5-kV (rms) input-output isolation and 25-kV transient immunity. It has less than 2 ns of pulse-width distortion, and it consumes 30 mW of power at 25 Mbits/s. Designed for 3.3- and 5.0-V operation, the device is pin-compatible with some existing optocouplers.

Two grades are available. The ADuM1100A delivers a 25-Mbit/s data rate, while the ADuM1100B offers a 100-Mbit/s rate. Both come in 8-lead SOICs. Sampling now, production is slated for this fall. Model A costs $2.50 and model B is $3.50, both in 10,000-unit quantities.

Analog Devices Inc., Two Technology Way, Norwood, MA 02062; (781) 461-3732; www.analog.com/umic.

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