Synchronous step-down switching regulator offers 94% efficiency

17th October 2017
Alice Matthews

A dual 4A, 42V input synchronous step-down switching regulator has been announced by Analog Devices, which recently acquired Linear Technology. The LT8650S's Silent Switcher2 architecture uses four internal input capacitors as well as two internal BST and a single INTVCC capacitor to minimise the area of the hot loops. Combined with well controlled switching edges and an internal construction using copper pillars in lieu of bond wires and an integral ground plane, the LT8650S’s design reduces EMI emissions.

This improved EMI performance is not sensitive to PCB layout, simplifying design and reducing risk even when using two layer PC boards. The LT8650S can 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 levels further.

The LT8650S’s synchronous rectification delivers efficiency as high as 94.6% with a switching frequency of 2MHz. Its 3.0-42V input voltage range is suitable for automotive and industrial applications. The internal high efficiency switches can deliver up to 4A of continuous output current simultaneously and up to 6A peak loads on either channel to output voltages as low as 0.8V. The LT8650S’s Burst Mode operation ensures only 6.2µA of quiescent current (for both channels), well suited for applications such as automotive always-on systems, which require extended operating battery life. The LT8650S’s fast minimum on-time of only 40ns enables 2MHz constant frequency switching from a 16V input to a 2V output, enabling designers to optimise efficiency while avoiding critical noise-sensitive frequency bands. The LT8650S’s 32-lead 4x6mm LQFN package and high switching frequency keeps external inductors and capacitors small, providing a compact, thermally efficient footprint.

The LT8650S utilises internal top and bottom high efficiency power switches with the necessary boost diodes, 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 very fast transient response or current sharing of the two channels, external VC pins are available. For the lowest noise operation, the LT8650S can be programmed to run in forced continuous mode over the entire load range with spread spectrum frequency modulation. Its switching frequency is programmable and synchronisable from 300kHz to 3MHz. Special design techniques and a new high speed process enable high efficiency over a wide input voltage range, and the LT8650S’s current mode topology enables fast transient response and excellent loop stability. Other features include a die temperature monitor, power good flags, output soft-start/tracking and thermal protection.

The LT8650SEV is packaged in a 4x6mm LQFN package. An industrial temperature version, the LT8650SIV, is tested and guaranteed to operate from a -40 to 125°C operating junction temperature.

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