Synchronous step-down converter with 95% efficiency at 2MHz 

April 17, 2017 // By Nick Flaherty
LT8640S
Analog Devices, which recently acquired Linear Technology, has launched a 6A, 42V input synchronous step-down switching regulator.

The Silent Switcher 2 architecture in the LT8640S uses two internal input capacitors as well as internal BST and INTVCC capacitors to minimize the area of the hot loops. Combined with very well controlled switching edges and an internal construction with an integral ground plane and the use of copper pillars in lieu of bond wires, the design dramatically reduces EMI/EMC emissions. This improved EMI/EMC performance is not sensitive to board layout, simplifying design and reducing risk even when using two layer PC boards, allowing it to pass the automotive CISPR 25, Class 5 peak EMI limits with a 2MHz switching frequency over its entire load range. Spread spectrum frequency modulation is also available to lower EMI/EMC levels further.

The LT8640S’s synchronous rectification delivers efficiency as high as 95% with a switching frequency of 2MHz. Its 3.4V to 42V input voltage range is ideal for automotive and industrial applications. The internal high efficiency switches can deliver up to 6A of continuous output current and peak loads of 7A to voltages as low as 0.97V. The Burst Mode operation uses 2.5µA of quiescent current, well suited for applications such as automotive always-on systems to extend operating battery life.

The design maintains a minimum dropout voltage of only 100mV (at 1A) under all conditions, enabling it to excel in scenarios such as automotive cold-crank. Furthermore, a fast minimum on-time of only 30ns enables 2MHz constant frequency switching from a 16V input to a 1.5V output, enabling designers to optimize efficiency while avoiding critical noise-sensitive frequency bands. The 24-lead, LQFN package and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint.