72V fixed-ratio DC/DC controller eliminates power inductor
A high power fixed ratio charge pump DC/DC controller that eliminates the power inductor in a non-isolated intermediate bus converter has been released from Analog Devices as the LTC7820, which allows up to a 50% reduction in circuit size and up to 4000W/in3 power density.
Analog Devices, who recently acquired Linear Technology, designed the LTC7820 to drive external MOSFETs in voltage divider, doubler or inverter configurations with an efficiency of up to 99%. Its open loop fixed duty is suitable for non-isolated intermediate bus applications in power distribution, datacom, telecom, high-end computing and industrial systems.
The LTC7820 operates over a 6-72V (80V abs max) input voltage range and can produce output currents in multiple 10s of amps, depending on the topology and choice of external components.It can be configured for a 2:1 step-down ratio from an input voltage up to 72V.
Two of the LTC7820 IC’s can be cascaded for a 4:1 step-down ratio. For even higher step-down ratios, such as a 6:1, the Dickson converter topology is recommended and is ideal for 54V input to a 9V outputs, requiring only a single LTC7820. The LTC7820 can also be configured for a 1:2 step-up ratio or a 1: 1 inverter ratio from an input voltage as high as 36V.External MOSFETs switch at a fixed frequency, programmable from 100kHz to 1MHz. The LTC7820’s powerful 1.1Ω N-channel MOSFET gate drivers maximise efficiency and can drive multiple MOSFETs in parallel for higher power applications.
The LTC7820 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 permits the LTC7820 to be powered from the lower voltage output of the converter or other available sources up to 40V, reducing power dissipation and improving efficiency. Additional features include soft switching for low EMI, a power good output signal, undervoltage lockout and internal charge balance circuitry.
The LTC7820 is available in a 4x5mm QFN-28 package. Extended and industrial temperature versions are available from –40 to 125°C.