42V, 5A switching regulator produces ultralow EMI/EMC emissions

December 12, 2014 // By Graham Prophet
LT8640 is a 5A, 42V input-capable synchronous step-down switching regulator. Its “Silent Switcher” architecture, combined with spread spectrum frequency modulation, reduces EMI/EMC emissions by more than 25 dB even with switching frequencies in excess of 2 MHz, enabling it to pass the automotive CISPR25, Class 5 peak limits.

Synchronous rectification delivers efficiency as high as 95% with a switching frequency of 2 MHz. Its 3.4V to 42V input voltage range suits it to automotive and industrial applications. The LT8640's internal high efficiency switches deliver up to 5A of continuous output current and peak loads of 7A to voltages as low as 0.97V. The device's Burst Mode operation keeps quiescent current under 2.5 µA in no-load standby conditions, suiting it for applications such as automotive "always-on" systems, which need to extend operating battery life. The device's design maintains a minimum dropout voltage of 100 mV at 1A under all conditions including automotive cold-crank. Fast minimum on-time of 40nsec enables 2 MHz constant frequency switching from a 16V input to a 1.5V output, equipping designers to optimise efficiency while avoiding critical noise-sensitive frequency bands. The LT8640's 20-lead 3 x 4 mm QFN package and high switching frequency keep external inductors and capacitors small, providing a compact, thermally efficient footprint.

The LT8640 has internal top and bottom high efficiency power switches with the necessary boost diode, oscillator, control and logic circuitry, integrated into a single die. Low ripple Burst Mode operation maintains high efficiency at low output currents while keeping output ripple below 10 mVPK-PK. High efficiency is maintained over a wide input voltage range, and the chip's current-mode topology enables fast transient response and excellent loop stability. Other features include internal compensation, a power-good flag, output soft-start/tracking and thermal protection.

The LT8640EUDC is packaged in a 3 x 4 mm QFN package at $4.35 (1000). Industrial and automotive temperature versions are available.

Linear Technology; www.linear.com/product/LT8640