Hybrid DC/DC controller reduces solution size by half

10th January 2018

Analog Devices

Lanna Deamer

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Datasheet

Analog Devices has announced a hybrid step-down synchronous controller that merges a switched capacitor circuit with a synchronous step-down controller, the Power by Linear LTC7821, enabling up to a 50% reduction in DC/DC converter solution size compared to traditional step-down solutions. This improvement is enabled by a three times higher switching frequency without compromising efficiency.

Alternatively, when operating at the same frequency, a LTC7821-based solution can provide up to three percent higher efficiency.

Other benefits include low EMI and reduced MOSFET stress due to a soft-switched front end, suitable for next-gen non-isolated intermediate bus applications in power distribution, datacom and telecom as well as emerging 48V automotive systems.

The LTC7821 operates over a 10-72V (80V abs max) input voltage range and can produce an output voltage from 0.9-33.5V with currents in multiple 10s of amps, depending on the choice of external components.In a typical 48-12V/20A application, an efficiency of 97% is attainable with the LTC7821 switching at 500kHz.

The same efficiency can only be achieved in a traditional synchronous step-down converter by switching at one-third the operating frequency, resulting in the use of much larger magnetics and output filter components. External MOSFETs switch at a fixed frequency programmable from 200kHz-1.5MHz.

The LTC7821’s powerful 1Ω N-channel MOSFET gate drivers maximise efficiency and can drive multiple MOSFETs in parallel for higher power applications. Due to its current mode control architecture, multiple LTC7821s can be operated in a parallel, multiphase configuration with excellent current sharing to enable much higher power applications.

The LTC7821 implements many proprietary protection features for robust performance in a wide range of applications. An LTC7821-based design eliminates the inrush current typically associated with switched capacitor circuits by pre-balancing the capacitors during startup.

The LTC7821 also monitors system voltage, current and temperature for faults, and uses a sense resistor for overcurrent protection. It stops switching and pulls the /FAULT pin low when a fault condition occurs. An onboard timer can be set for appropriate restart/retry times. The EXTV_CC pin enables the LTC7821 to be powered from the lower voltage output of the converter or other available source up to 40V, reducing power dissipation and improving efficiency.