DC/DC controller meets automotive dual battery system needs

The LTC3871 is a 100/30V bi-directional, two-phase synchronous buck or boost controller, from Linear Technology. It is suitable for 48/12V automotive dual battery systems, where electrical content is increasing, leading to the proposed standard, LV148. This combines a secondary 48V bus with the existing 12V system.

The 48V rail includes a belt starter generator (BSG) or an integrated starter generator (ISG), a 48V Li-Ion battery and a bi-directional DC/DC converter to deliver up to 10kW from the 48 and 12V batteries combined. This technology targets conventional internal combustion automobiles, as well as hybrid electric vehicles to meet CO2 emissions targets.

The controller provides bi-directional DC/DC control and battery charging between the 12 and 48V board nets. It operates in buck mode from the 48V bus to the 12V bus, or in boost mode from 12 to 48V. Either mode is configured on demand with a control signal. Up to 12 phases can be paralleled and clocked out-of-phase to minimise input and output filtering requirements for high current applications (up to 250A). The current mode architecture is claimed to provide ‘excellent’ current matching between phases when paralleled. Up to 3kW can be supplied in buck mode or in boost mode with a 12-phase design.

The controller allows both batteries to supply energy simultaneously by converting energy from one board net to the other. Typically, the 12V bus will continue to power the ignition, lighting, infotainment and audio systems. The 48V bus will supply active chassis systems, power steering, air conditioning compressors, electric superchargers/turbos and support regenerative braking. Up to 97 per cent efficiency can be achieved and the on-chip current programming loop regulates the maximum current that can be delivered to the load in either direction. Two control loops for current and two for voltage, enable control of voltage and current on either the board nets.

Operating at a selectable fixed frequency between 60 and 460kHz, the device can be synchronised to an external clock over the same range. The user can select continuous operation, or pulse-skipping during light loads. Additional features include over-load and short-circuit protection, independent loop compensation for buck and boost, ± one per cent voltage regulation accuracy over-temperature, under-voltage and over-voltage lockout. The controller has been qualified to meet AEC-Q100 specifications and to ISO-26262.

It is available in a thermally enhanced 48-lead LQFP and with three temperature grades: extended, industrial and automotive ranges.



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