Analog Devices Inc.

Demonstration circuit 2513B is a high efficiency, high power density hybrid converter. It can deliver 12V/20A with an input voltage from 36V to 72V. This demo board features the LTC7821, which uses an architecture that merges soft-switching switched-capacitor topology with a traditional step-down converter to provide superior efficiency compared to the traditional switching architectures. It offers a high efficiency/high density and cost effective solution for nonisolated intermediate bus applications in power distribution, datacom and telecom as well as emerging 48V automotive systems. External MOSFETs switch at a 500kHz fixed frequency for this demo board and can be programmed from 200kHz to 1.5MHz. The LTC7821’s powerful 1Ω 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 and low output voltage ripple to enable much higher power applications. Other benefits include low EMI emissions due to a soft-switched front end and reduced MOSFET stress. The LTC7821 design eliminates the inrush current typically associated with switched capacitor circuits by prebalancing the capacitors on 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. Additional features include ±1% output voltage accuracy over temperature, a clock output for multiphase operation, a power good output signal, short-circuit protection, monotonic output voltage start-up, optional external reference, undervoltage lockout and internal charge balance circuitry. The LTC7821 data sheet must be used in conjunction with this demo board manual.

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