65V/8A synchronous step-down switching regulator delivers 94% efficiency at 2MHz

65V/8A synchronous step-down switching regulator delivers 94% efficiency at 2MHz

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By Nick Flaherty

The Silent Switcher2 architecture in the LT8645S 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 internal construction with an integral ground plane and the use of copper pillars in lieu of bond wires, the LT8645S reduces EMI/EMC emissions and is independent of board layout, simplifying design and reducing risk even when using two layer PC boards, allowing designs to pass the automotive CISPR25, Class 5 peak EMI limits with a 2MHz switching frequency over the entire load range. Spread spectrum frequency modulation is also available to lower EMI/EMC levels further.

The LT8645S’s synchronous rectification delivers efficiency as high as 94% with a switching frequency of 2MHz. Its 3.4V to 65V input voltage range is ideal for dual cell transportation, 48V automotive and industrial applications. The internal high efficiency switches can deliver up to 8A of continuous output current at voltages as low as 0.97V. Burst Mode operation provides  2.5µA of quiescent current for applications such as automotive/transportation always-on systems which need to extend operating battery life.

The device design maintains a minimum dropout voltage of only 60mV (at1A) under all conditions, enabling it to excel in scenarios such as automotive cold-crank. Furthermore, a fast minimum on-time of only 40ns enables 2MHz constant frequency switching from a 24V input to a 2.0V output with small inductors, enabling designers to optimize efficiency while avoiding critical noise-sensitive frequency bands.

The LT8645S 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 LT8645S can be programmed to run in pulse-skipping mode. Its switching frequency is programmable and synchronizable from 200kHz to 2.2MHz. Other features include internal compensation, a power good flag, output soft-start/tracking and thermal protection.

The LT8645SEV is packaged in a 4mm x 6mm LQFN package. An industrial temperature version, the LT8645SIV, is tested and guaranteed to operate from a –40°C to 125°C operating junction temperature. Pricing starts at $5.95 each for 1,000-piece quantities and both versions are available from stock.

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