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48V/12V DC/DC for automotive dual-rails offers bidirectional power flows

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By Graham Prophet


Either mode is configured on demand with 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). Its advanced current mode architecture provides current matching between phases when paralleled. Up to 3 kW can be supplied in buck mode or in boost mode with a 12-phase design.

 

Current 12V automotive systems, Linear notes, are reaching their 3 kW power limit due to the ever-increasing demand for more electrical devices. A newly proposed standard, LV148, 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 lithium-ion battery and a bidirectional DC/DC converter for delivery of up to 10 kW of available energy from the 48V and 12V batteries combined. This technology is targeted for conventional internal combustion cars, as well as hybrid electric and mild hybrid vehicles.

 

When starting the car or when additional power is required, the LTC3871 allows both batteries to supply energy simultaneously by converting energy from one boardnet 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% 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. Four control loops, two for current and two for voltage, enable control of voltage and current on either the 48V or 12V boardnets.

 

The LTC3871 operates at a selectable fixed frequency between 60 kHz and 460 kHz, and can be synchronized to an external clock over the same range. The user can select from continuous operation or pulse-skipping during light loads. Additional features include overload and short-circuit protection, independent loop compensation for buck and boost, EXTVCC for increased efficiency, ±1% voltage regulation accuracy over temp, along with undervoltage and overvoltage lockout. The LTC3871 has been qualified to meet AEC-Q100 specifications and was designed with intrinsic safety being fully considered in line with the ISO-26262 standard.

 

The LTC3871 is available in a thermally enhanced 48-lead LQFP package. Three temperature grades are available, with operation from –40°C to 125°C for the extended and industrial grades and a high temp automotive range of –40°C to 150°C. The 1,000-piece price starts at $5.40 each.

 

Linear Technology; www.linear.com/product/LTC3871

 

 

 


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