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Analog Angle Article

IC current source solves myriad problems, attenuates headaches

Milpitas, Calif.–Sometimes, the most “innovative” product is not one which packs more functions into the package, has increased speed, or is cheaper, but instead is one which solves a conceptually small but chronic problem for the circuit designer by doing one thing, doing it well, and not getting in the way of the user's objectives. The LT3092 current source from Linear Technology Corp. is an example.

Designed by LTC's Vice President of Engineering and Chief Technology Officer Robert Dobkin, the LT3092 is a two-terminal current source. That's it. It provides resistor-programmable current between 0.5 mA and 200 mA and can be paralleled (using a 40 mΩ resistance, usually just a PCB trace) for greater total current. It is an easy-to-use, higher-performance alternative to conventional, finicky current-source designs based on depletion-mode FETs or two-transistor, two-Zener diode approaches. (If you have ever designed a good current source, you know it takes a lot of careful effort and circuitry to implement what is represented symbolically by the simple symbol of two interlocked circles and an arrow!)

The core of the design is the innovative three-terminal LT3080 low-dropout regulator, also designed by Dobkin, and introduced about a year ago. The current source does not require any input or output capacitors and thus can be used in “intrinsically safe” applications (no stored charge or energy) as well as floating applications such as the ubiquitous current loop. The absence of any capacitors also means that both AC and DC impedances are high and maintained, even when connected is series with unknown reactance; impedance is 100 MΩ at 1 mA and 1 MΩ at 100 mA



Regulation over the 1.2 to 40 V supply range is better than 10 ppm/V, and the IC includes reverse-battery and reverse-current protection. Initial set-pin current accuracy is 1%. Additional key typical specs include load regulation of better than 1 mV, and line regulation of better than 0.001%/V.

Packaging, pricing, and availability : The LT3092 is available now, in 3 mm × 3 mm DFN-8, 8-lead TSOT-23, and 3-lead SOT-223 packages. Operating ranges including -40°C to +125°C and -55°C to +125°C junction temperatures. Pricing begins at $1.65.–Bill Schweber

For more information , contact Linear Technology Corp, http://www.linear.com.

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