Boost and buck synchronous DC/DC controller maintains regulation in automotive systems

Linear Technology Corporation has produced the LTC7812, a dual output (boost + buck), low quiescent current synchronous DC/DC controller. When cascaded, its independent step-up (boost) and step-down (buck) controllers regulate the output voltage from an input voltage that can be above, below or equal to the output voltage, maintaining output regulation during cold crank and load dump conditions. Unlike conventional single inductor buck-boost regulators, the LTC7812’s cascaded boost and buck solution provides fast transient response with continuous, non-pulsating, input and output currents, substantially reducing ripple voltage and electromagnetic interference (EMI), making it ideal for automotive, industrial and high-power battery-operated systems.

The LTC7812 operates from an input voltage of 4.5V to 38V and maintains operation down to 2.5V after start-up. The synchronous boost converter can produce output voltages up to 60V and can run at 0 per cent duty cycle (synchronous switch ON) to pass through the input voltage when required for maximum efficiency. The step-down converter can produce output voltages from 0.8V to 24V with an efficiency as high as 98 per cent. In addition, the LTC7812 can be configured for Burst Mode operation, reducing quiescent current to 28µA with the buck channel on (33µA for both channels on) in sleep mode, a useful feature for preserving battery run time. The powerful 1Ω onboard all N-channel gate drivers minimise MOSFET switching losses and provide an output current of more than 10 amps per channel, limited only by external components. The output current for each converter is sensed by monitoring the voltage drop across the inductor (DCR) or by using a separate sense resistor.

The LTC7812’s constant frequency current mode architecture enables a selectable frequency from 50kHz to 900kHz or it can be synchronised to an external clock from 75kHz to 850kHz. Additional features include adjustable soft-start or tracking, foldback current limit, output overvoltage protection, run control and a power good output voltage signal.                                                                                                                   The LTC7812 is available in a 32-lead 5mm x 5mm QFN package. The 1,000-piece price starts at $4.00 each.