Synchronous step-down silent switcher 2 delivers very high efficiency and ultralow EMI/EMC emissions

19-04-2017 | Linear | Power

Linear Technology has announced the LT8640S, a 6A, 42V input synchronous step-down switching regulator. Its unique Silent Switcher 2 architecture 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. The device can easily 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 device’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 offers only 2.5µA of quiescent current, well suited for applications such as automotive always-on systems, which need to extend operating battery life. The unique 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, 4mm x 4mm LQFN package and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint.

The device utilizes 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 10mVP-P. For applications requiring the lowest noise operation, the device can be programmed to run in forced continuous mode over the entire load range. Its switching frequency is programmable and synchronizable from 200kHz to 3MHz. Special design techniques and a new high speed process enable high efficiency over a wide input voltage range, and the 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.

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