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Ultralow EMI/EMC noise, automotive step-down rated 65V & 8A output

Ultralow EMI/EMC noise, automotive step-down rated 65V & 8A output

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By Christoph Hammerschmidt



The device’s 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 internal construction with an integral ground plane and the use of copper pillars in place of bond wires, the LT8645S 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 LT8645S can easily pass the automotive CISPR25, Class 5 peak EMI limits with a 2 MHz switching frequency over its 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 2 MHz. Its 3.4V to 65V input voltage range is suitable for dual cell transportation, 48V automotive and industrial applications. The internal high efficiency switches can deliver up to 8A of continuous output current to voltages as low as 0.97V. The LT8645S’s Burst Mode operation enables 2.5 µA of quiescent current, for applications such as automotive/transportation always-on systems. The LT8645S’s design maintains a minimum dropout voltage of 60 mV (at1A) under all conditions, for scenarios such as automotive cold-crank. A fast minimum on-time of 40 nsec enables 2 MHz constant frequency switching from a 24V input to a 2.0V output, enabling designers to optimize efficiency while avoiding critical noise-sensitive frequency bands. The LT8645S’s 32-lead, 4 x 6 mm LQFN package and high switching frequency keeps external inductors and capacitors small.

 

The LT8645S 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 10 mVP-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 200 kHz to 2.2 MHz. LT8645’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.

 

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 (1000).

 

Analog Devices/Linear Technology; www.linear.com/product/LT8645S

 

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