Synchronous step-down DC/DC offers 93% efficiency at automotive voltages

October 28, 2014 // By Graham Prophet
LT8609 is a 2A, 42V input synchronous step-down switching regulator, with a synchronous rectification topology that delivers 93% efficiency while switching at 2 MHz enabling designers to avoid critical noise-sensitive frequency bands, such as AM radio, while providing a compact footprint.

Burst Mode operation keeps quiescent current under 2.5 µA in no-load standby conditions, making it suitable for always-on systems. The LT8609's 3.0V to 42V input voltage range enables use in automotive applications which must regulate through cold-crank and stop-start scenarios with minimum input voltages as low as 3.0V and load dump transients in excess of 40V. Its internal 3.5A switches can deliver up to 2A of continuous output current with peak load currents of 3A.

The LT8609 maintains a minimum dropout voltage of 200 mV (at 1A) under all conditions, enabling it to excel in scenarios such as automotive cold-crank. Spread spectrum frequency modulation and special design techniques offer low-EMI operation to minimise noise concerns in automotive and industrial environments. A fast minimum on-time of 45 nsec enables 2 MHz constant frequency switching from a 16V input to a 1.5V output. The LT8609's 10-lead thermally enhanced MSOP package and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint.

The LT8609 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 mVp-p. Its design techniques and a new high speed process enable high efficiency over a wide input voltage range, and the LT8609’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 LT8609EMSE is packaged in thermally enhanced MSOP-10 package for $2.50: an industrial temperature version, LT8609IMSE, operates from -40°C to 125°C operating junction temperature and is priced at $2.75 (both 1000).

Linear Technology;  www.linear.com/product/LT8609