100V/30V bidirectional 2-phase DC/DC controller ideal for dual battery systems

Linear Technology Korea (CEO: Hong Sa-kwak) has introduced a new 100V/30V bidirectional 2-phase synchronous buck or boost controller (product name: LTC3871), ideal for 48V/12V automotive dual battery systems.

Current 12V automotive systems are approaching their 3kW power limit as power demand continues to increase due to the increasing use of electronic devices in vehicles. The newly emerging LV148 standard combines a secondary 48V bus with the existing 12V system.

This 48V rail integrates a Belt Starter Generator (BSG) or Integrated Starter Generator (ISG), a 48V lithium-ion battery, and a bidirectional DC/DC converter to provide up to 10kW of available energy from the combined power source of the 48V and 12V batteries.

As automakers work to meet increasingly stringent carbon dioxide emission standards, the technology could be used in hybrid electric vehicles and mild hybrid vehicles in addition to traditional internal combustion engine vehicles.

“Running electrical systems in automobiles at 48V will play a key role in increasing available energy while reducing wiring harness weight and power loss,” said Don Paulus, vice president of power management products for Linear Technology. “This additional energy capacity will open the way for new technologies to be introduced into automobiles that will improve safety and efficiency without compromising performance.”

The LTC3871 provides bidirectional DC/DC control and battery charging between 12V and 48V. The device operates in buck mode from the 48V bus to the 12V bus, or in boost mode from 12V to 48V. Each mode is configured on demand by an applied control signal. Up to 12 phases can be paralleled and clocked out of phase to minimize input and output filtering requirements for high current applications (up to 250A). The advanced current-mode architecture provides excellent current matching between phases in a parallel configuration. For a 12-phase design, up to 3 kW can be supplied in buck or boost mode.

When starting or when additional power is required, the LTC3871 allows two batteries to supply energy simultaneously by converting energy from one boardnet to the other. Typically, the 12V bus continues to power the ignition, lighting, infotainment and audio systems, while the 48V bus powers the active chassis systems, power steering, air conditioning compressor, electric supercharger/turbo and supports regenerative braking.

Conversion efficiency is up to 97%, and the on-chip current programming loop controls the maximum current that can be delivered to the load in either direction. There are four control loops, two for current and two for voltage, allowing voltage and current control for either the 48V or 12V boardnets.

The LTC3871 operates at a selectable fixed frequency from 60kHz to 460kHz and is synchronizable to an external clock over the same range. The user can select either continuous operation or pulse-skipping operation during light loads. Additional features include overload and short-circuit protection, separate loop compensation for buck and boost, EXTVCC for enhanced efficiency, ±1% voltage regulation over temperature, undervoltage (UVLO) and overvoltage lockout (OVLO). The LTC3871 is AEC-Q100 qualified and is designed for intrinsic safety in compliance with the ISO 26262 standard.

The LTC3871 is available in a thermally enhanced 48-lead LQFP package. Three temperature grades are available, with extended and industrial grades operating from –40°C to 125°C and an automotive high-temperature grade operating from –40°C to 150°C. Pricing starts at $5.40 each in 1,000-piece quantities.