Low Iq automotive twin-output boost + buck DC/DC controller

March 31, 2016 // By Graham Prophet
LTC7813 is 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, including during an automotive load dump or cold crank.


Unlike conventional single inductor buck-boost regulators, the LTC7813’s cascaded boost + buck solution provides fast transient response with continuous, non-pulsating input and output currents. It substantially reduces ripple voltage and EMI, ideal for automotive, industrial and high power battery operated systems.


The LTC7813 operates from an input voltage of 4.5V to 60V during start-up and maintains operation down to a 2.2V input after start-up. The boost converter can produce an output voltage up to 60V and the buck converter produces an output voltage ranging from 0.8V to 60V with the entire system achieving an efficiency as high as 98%. In addition, this device can be configured for Pass-Through or Wire Mode with the synchronous Boost MOSFET continuously on and the buck converter running at 99% duty cycle resulting in the input voltage being passed to the output with minimal voltage drop.


The LTC7813 can be configured for Burst Mode operation, reducing quiescent current to 29 µA with the buck channel on (34 µA for both on) in sleep mode, a useful feature for preserving battery run times. The powerful 1Ω onboard all N-channel gate drivers minimise MOSFET switching losses and provide an output current of more than 10A 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 LTC7813’s current mode architecture enables a fixed selectable frequency from 50 kHz to 900 kHz or it can be synchronised to an external clock from 75 kHz to 850 kHz. Additional features include adjustable gate drive voltage, soft-start or tracking, and foldback current limit, output overvoltage protection, run control and a power-good output signal.


The LTC7813 is available in a 32-lead 5 x 5 mm QFN package for $4.82 (1,000).


Linear Technology; www.linear.com/product/LTC7813