Extended operating temperatures for 80V buck-boost DC/DC controller

August 07, 2014 // By Graham Prophet
H- and MP-grade versions of the LT8705, a 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, are guaranteed over operating junction temperatures from -40°C to 150°C and -55°C to 150°C, respectively.

The LT8705 operates over a 2.8V to 80V input voltage range and produces a fixed 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 power can be achieved when multiple circuits are paralleled.

The LT8705 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 operating frequency is selectable between 100 kHz and 400 kHz, and can be synchronised to an external clock. The LT8705 employs a current-mode control architecture for constant-frequency operation in buck or boost mode and has onboard quad N-channel MOSFET gate drivers. The user can select among forced continuous, discontinuous and Burst Mode operation to maximise light load efficiency.

Additional features include servo pins to indicate which feedback loops are active, a 3.3V/12 mA LDO, adjustable soft-start, onboard die temperature monitor and ±1.30% reference voltage accuracy over an operating junction temperature range of -55°C to 150°C. The LT8705 is available in a 38-pin 5 x 7 mm QFN, and also a 38-lead TSSOP package with additional pin spacing for high voltage operation. Pricing starts at $6.83 (1,000).

Linear Technology; www.linear.com/product/LT8705