Chip converts input voltages from 2.8V to 80V to fixed output voltage at high efficiency

February 13, 2013 // By Christoph Hammerschmidt
A very high efficiency and an unusually wide input voltage range are the main characteristics of Linear Technology's new LT8705 synchronous buck-boost DC/DC controller. The device can be used in a wide range of applications such as a voltage stabilizer in telecom and automotive requirements, as well as in solar or high impedance sources and battery systems.

Linear announces the LT8705, a very high efficiency (up to 98%) synchronous buck-boost DC/DC controller that operates from input voltages above, below or equal to the regulated output voltage. This device has four feedback loops to regulate the input current/voltage, along with the output current/voltage. The input current and voltage feedback loops can prevent overloading of solar cells. The output current loop provides a regulated output current for a battery charger or current source.

The LT8705 operates over a wide 2.8V to 80V input voltage range and produces a 1.3V to 80V output, using a single inductor with 4-switch synchronous rectification. Output power up to 250W can be delivered with a single device. Higher output power can be achieved when multiple circuits are paralleled. The operating frequency is selectable between 100kHz and 400kHz, and can be synchronized to an external clock. The LT8705 employs a proprietary current-mode control architecture for constant frequency operation in buck or boost mode and has powerful onboard quad N-channel MOSFET gate drivers. The user can select among forced continuous, discontinuous and Burst Mode operation to maximize light load efficiency.

Additional features include servo pins to indicate which feedback loops are active, a 3.3V/12mA LDO, adjustable soft-start, onboard die temperature monitor and ±1% reference voltage accuracy over an operating junction temperature range of -40°C to 125°C. The LT8705 is available in a 38-pin 5mm x 7mm QFN, and also a 38-lead TSSOP package with additional pin spacing for high voltage operation. Pricing starts at $5.95 each in 1,000-piece quantities. 

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