Synchronous step-down switching regulator minimises hot loops

Delivering 95 per cent efficiency at 2MHz, the LT8650S is a dual 4A, 42V input synchronous step-down switching regulator, released by Analog Devices.

Its Silent Switcher 2 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, says Analog Devices. Combined with very 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. EMI performance is not sensitive to PCB layout, which simplifies design and reduces the risk even when using two layer PC boards, claims Analog Devices. The LT8650S passes 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 per cent with a switching frequency of 2MHz. Its 3.0 to 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 6.0A peak loads on either channel to output voltages as low as 0.8V.

Burst Mode operation ensures only 6.2-microA of quiescent current (for both channels), making the LT8650S suited to applications such as automotive always-on systems, which require extended operating battery life. The LT8650S’s fast minimum on-time of only 40-nano seconds enables 2MHz constant frequency switching from a 16V input to a 2.0V output. According to Analog Devices, this enables designers to optimise efficiency while avoiding critical noise-sensitive frequency bands. The LT8650S’s 32-lead 4.0 x 6.0mm LQFN package and high switching frequency keeps external inductors and capacitors small in size, adds Analog Devices.

The LT8650S uses internal top and bottom high efficiency power switches with 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 load range with spread spectrum frequency modulation. Its switching frequency is programmable and synchronisable from 300kHz to 3MHz. The LT8650S’s current mode topology enables fast transient response and loop stability. Other features include a die temperature monitor, power good flags, output soft-start/tracking and thermal protection.

An industrial temperature version, the LT8650SIV, is tested and guaranteed to operate from a   -40 to +125 degree C operating junction temperature.


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