New DC-DC controller maintains regulation in autos and truck start/stop systems

Linear Technology has introduced the LTC3899, a new triple-output (buck, buck, boost) 29µA quiescent current, synchronous DC-DC controller that maintains output voltage regulation over a 2.2V to 60V input range. A 12V vehicle battery can droop to less than 4V during engine restart or cold crank, causing reset of infotainment systems and other electronics that operate from 5V and higher. The boost converter feeds two step-down converters, avoiding output voltage dropout when a car battery droops, a useful feature in automotive start/stop systems that shut off the engine at idle to save fuel. The 60V maximum input voltage covers double battery truck applications. Alternatively, the buck controllers can be powered from the input as a general purpose triple output controller. The LTC3899 operates from an input voltage of 4.5V to 60V during start-up and maintains operation down to 2.2V after start-up. The boost and buck converters can produce output voltages up to 60V with efficiencies as high as 95%. In applications where the input voltage may exceed the regulated output voltage, the LTC3899 keeps the synchronous boost MOSFET on continuously so that the output voltage follows the input voltage with minimal power loss. In addition, the LTC3899 can be configured for Burst Mode operation, reducing quiescent current to 29µA for one channel (39µA for all three channels on) with outputs in regulation in standby mode, a useful feature for preserving battery run times. The powerful 1ohm onboard all N-channel gate drivers minimize MOSFET switching losses and provide for output currents of more than 10 amps per channel, limited only by external components. Furthermore, the output current for each converter can be sensed by monitoring the voltage drop across the inductor (DCR) or by using a sense resistor. The LTC3899’s constant frequency current mode architecture enables a fixed frequency from 50kHz to 900kHz or it can be synchronized to an external clock from 75kHz to 850kHz. Additional features include an onboard LDO for IC power and gate drive, output voltage tracking or adjustable soft-start, a power good signal and an optional external VCC bias input. The LTC3899 is available in 38-lead SSOP and 38-pin 5mm x 7mm QFN packages. Four temperature grades are available, with operation from -40C to 125C. For extended and industrial grades, a higher temperature automotive grade of -40C to 150C and a MIL grade of -55C to 150C are offered.