Analog Devices’ Silent Switcher 2 architecture LT8640S reduces EMI/EMC

Analog Devices, which recently acquired Linear Technology, offers the LT8640S, 6.0A, 42V input synchronous step-down switching regulator. Its Silent Switcher 2 architecture uses two internal input capacitors as well as internal BST and INTVCC capacitors to minimise the area of the hot loops.

Analog Devices explains that the architecture, together with well-controlled switching edges and an internal construction with an integral ground plane, coupled with the use of copper pillars in lieu of bond wires, enable the LT8640S’s design to dramatically reduce EMI/EMC emissions. The improved EMI/EMC performance is not sensitive to board layout, which simplifies design and reduces risk even when using two layer printed circuit boards, says Analog Devices.

The LT8640S can pass the automotive CISPR 25, Class 5 peak EMI limits with a 2.0MHz 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 per cent with a switching frequency of 2.0MHz. The 3.4 to 42V input voltage range is suitable for automotive and industrial applications. The internal high efficiency switches can deliver up to 6.0A of continuous output current and peak loads of 7.0A to voltages as low as 0.97V. The LT8640S’s Burst Mode operation offers only 2.5-microA of quiescent current, suitable for applications such as automotive always-on systems, which need to extend operating battery life. The LT8640S maintains a minimum dropout voltage of only 100mV (at 1.0A) under all conditions, for automotive cold-crank operation. A fast minimum on-time of only 30ns enables 2.0MHz constant frequency switching from a 16 input to a 1.5V output, enabling designers to optimise efficiency while avoiding critical noise-sensitive frequency bands, says Analog Devices.

The LT8640S’s 24-lead, 4.0 x 4.0mm LQFN package and high switching frequency keeps external inductors and capacitors small, says Analog Devices, to deliver a compact, thermally efficient footprint.

The LT8640S uses 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 LT8640S can be programmed to run in forced continuous mode over the entire load range. Its switching frequency is programmable and synchronisable from 200kHz to 3.0MHz. The LT8640’s current mode topology enables fast transient response and excellent loop stability, says Analog Devices. Other features include internal compensation, a power good flag, output

soft-start/tracking and thermal protection.

An industrial temperature version, the LT8640SIV, is tested and guaranteed to operate from a -40 to +125 degree C operating junction temperature.


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