Linear step-down regulators offer ultra-low quiescent current

NEW YORK—Linear Technology [Milpitas, Calif.] has expanded its growing family of sub-5 µA quiescent current step-down regulators with a pair of devices aimed at the automotive and industrial sectors.

Linear Technology’s two latest devices include the LT3975, which is 42V step-down switching regulator that can deliver 2.5A of continuous output current and requires 2.7µA of quiescent current. And the 40-V, LT3976, which delivers up to 5A of output current and requires 3.3µA of quiescent current.

Both devices offer a 4.2V to a nominal 40V input voltage range, making them ideal for automotive and industrial applications. Their internal 75mOhm switches deliver efficiencies as high as 90%.

The LT3975’s and LT3976’s Burst Mode operation offers ultra-low quiescent current, a feature that is also well suited for automotive and industrial systems applications that demand always-on operation and optimum battery life.

The quiescent current levels are so low that it guarantees automotive and industrial designers will be under total budget for "always-on" systems, such as keyless lock entry and global positioning systems, in terms of its current draw when it's in stand-by mode, said Tony Armstrong, Director of Product Marketing for Power Products.

"The very low quiescent current in standby mode for always-on systems is sub-5 microamps, which is five times anything that we have and 10 times better from competition," Armstrong said.

The devices' design maintains a minimum dropout voltage of only 500mV when the input voltage drops below the programmed output voltage, a functional necessity in applications subject to automotive cold-crank conditions. Switching frequency is user-programmable from 200kHz to 2MHz, and synchronizable from 250kHz to 2MHz, enabling the designer to optimize efficiency while avoiding critical noise-sensitive frequency bands.

"One of the things that Linear Tech has been able to incorporate in this family of product is a very low switching minimum on time, which allows the designer to switch at 2 MHz and still go from 12 volts to 3.3 volts and maintain load regulation," Armstrong said.

The combination of their 16-lead thermally enhanced MSOP package and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint.

"This is a good advantage for a switch mode power supply designer because he’s always space constrained," Armstrong said. "He would ideally like to switch above 2 MHz to get very small external components and a small solution size."

The LT3975EMSE and the LT3976EMSE are packaged in a thermally enhanced  MSOP-16, priced starting at $3.10 and $3.75 each, respectively for 1,000-piece quantities.

Datasheets: LT3975 and LT3976