60V, 3x output, buck/buck/boost DC/DC controller for light hybrids

March 10, 2015 // By Graham Prophet
Designed to maintain regulation in automotive and heavy truck start/stop systems, the LTC3899 is a triple output (buck, buck, boost) 29 µA quiescent current, synchronous DC/DC controller that maintains output voltage regulation over a 2.2V to 60V input range.

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 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.

The chip can be configured for Burst Mode operation, reducing quiescent current to 29 µA for one channel (39 µA for all three channels on) with outputs in regulation in standby mode, a useful feature for preserving battery run times. The 1- Ω 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. 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 50 kHz to 900 kHz or it can be synchronised to an external clock from 75 kHz to 850 kHz. 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