10 Jan 2018

Hybrid step-down controller reduces solution size by 50%

Analog Devices has announced the Power by Linear LTC7821, a hybrid step-down synchronous controller that merges a switched capacitor circuit with a synchronous step-down controller, enabling up to a 50% reduction in DC/DC converter solution size compared to traditional step-down solutions.

This improvement is enabled by a 3 times higher switching frequency without compromising efficiency. Alternatively, when operating at the same frequency, a LTC7821-based solution can provide up to 3% higher efficiency. Other benefits include low EMI and reduced MOSFET stress due to a soft-switched front end, ideal for next generation non-isolated intermediate bus applications in power distribution, datacom and telecom as well as emerging 48V automotive systems.

The LTC7821 operates over a 10V to 72V (80V abs max) input voltage range and can produce an output voltage from 0.9V to 33.5V with currents in multiple 10s of amps, depending on the choice of external components. In a typical 48V to 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 to 1.5MHz. The LTC7821’s powerful 1 Ohm N-channel MOSFET gate drivers maximize 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 start-up. 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 EXTVcc  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.

LTC7821 Product Features

  • Wide V in  Range: 10V to 72V, 80V Abs Max

  • V out Range: 0.9V to 33.5V

  • Up to 50% Reduction in Solution Size

  • Soft Switching for Low EMI and Reduced MOSFET Stress

  • Up to 97% Efficiency at 500kHz

  • PLL Fixed Frequency from 200kHz to 1.5MHz

  • Clock Output for Multiphase Operation

  • Powerful Quad N-Channel MOSFET Gate Drivers

  • Input Current Sensing & Overcurrent Protection

  • Short-Circuit Protection with Programmable Timer Retry

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