Electronic Design

Dual In-Amp And Signal Isolators Sweat The Small Stuff

Two separate announcements from Analog Devices illustrate the importance of little things in how a company creates its products. One is a small-footprint instrumentation amplifier that makes an unusual boast about its datasheet. The other is an isolator that isolates the signal path as well as sensor power.

The AD8222 is a dual version of ADI's AD8221 buffer for high-resolution analog-to-digital converters (ADCs). The chip was re-engineered so the die would fit into a 4- by 4-mm, 16-lead lead-frame chip-scale package (LFCSP) for space-constrained industrial applications with lots of channels. Spec-wise, it's better than similar duals and most singles.

More importantly, its datasheet tells engineers exactly what happens when they wire together the two amplifiers in the package to provide a differential output. That's how most engineers use these amplifiers, whether they're singles or duals. Every time until now, those engineers have had to characterize the circuit for themselves. Now they don't have to.

What ADI did was pretty simple. It wasn't necessary to create a demo board or a reference design. All it took was some characterization and some extra ink in the datasheet. Still, it makes a big difference.

The other IC is the latest of ADI's alternatives to optoisolators that are based on integrating planar transformers on silicon. Compared to optocouplers, they consume less power, achieve higher data rates, and provide more precise timing. What's new is that the dual-channel ADuM5240, ADuM5241, and ADuM5242 incorporate an isolated 5-V power supply for the sensor (see the figure).

The converter provides 5 V at up to 50 mW from supply voltages above 4.5 V. The signal channels have propagation delay less than 55 ns and channel-to-channel matching better than 3 ns. The isolation rating is 2.5 kV. Adding a dc-dc converter is a relatively little thing here too, once you have the isolation technology. But it means a lot to the engineers whose problem it solves.

The three isolators differ only in pinout. The 5240 signal outputs are on the same side as the power output. The 5241 has signal channels in each direction, which is good for bidirectional communications transceivers that also need isolated power for interface electronics. With its two signal outputs on the same side as the power input, the 5242 suits power-supply applications that use secondary side control and require isolated power to initiate startup.

Sampling now, the AD8222 will be available in volume in the third quarter. It costs $3.59 in lots of 1000. The digital isolators are now sampling to lead customers with open market samples in July. Pricing is $2.95 each.

Analog Devices

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