DC/DC controller targets automotive start/stop systems

Posted By : Siobhan O'Gorman
DC/DC controller targets automotive start/stop systems


The LTC3899, a triple output, 29µA quiescent current, buck/buck/boost synchronous DC/DC controller which maintains output voltage regulation over a 2.2-60V input range, has been introduced by Linear Technology.

A 12V car 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 for 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 range of 4.5-60V 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 controller 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 1Ω onboard all N-channel gate drivers minimise MOSFET switching losses and provide for output currents of more than 10A 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 or by using a sense resistor. The controller’s constant frequency current mode architecture enables a fixed frequency from 50 to 900kHz. Alternatively, the device can be synchronised to an external clock from 75 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 5x7mm QFN packages. Four temperature grades are available, with operation from -40 to 125°C for the extended and industrial grades, -40 to 150°C for the automotive grade and -55 to 150°C for the military grade. The 1,000-piece price starts at $4.95 each.


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