98% Efficient Bidirectional Buck-Boost Controller for 12V-12V Redundant Battery Systems in Autonomous Vehicles

Analog Devices announces the Power by Linear^™ LT8708/-1, a 98% efficient bidirectional buck-boost switching regulator controller that operates between two batteries that have the same voltage, which are ideal for redundancy in self-driving cars. The LT8708/-1 operates from an input voltage that can be above, below or equal to the output voltage, making it well suited for two each 12V, 24V or 48V batteries commonly found in electric and hybrid vehicles. It operates between two batteries and prevents system shutdown should one of the batteries fail. The LT8708/-1 can also be used in 48V/12V and 48V/24V dual battery systems.

The LT8708/-1 operates with a single inductor over a 2.8V to 80V input voltage range and can produce an output voltage from 1.3V to 80V, delivering up to several kilowatts of power depending on the choice of external components and number of phases. It simplifies bidirectional power conversion in battery/capacitor backup systems that need regulation of V_OUT, V_IN, and/or I_OUT, I_IN, both in the forward or reverse direction. This device’s six independent forms of regulation allow it to be used in numerous applications.

The LT8708-1 is used in parallel with the LT8708 to add power and phases. The LT8708-1 always operates as a slave to the master LT8708, can be clocked out-of-phase and has the capability to deliver as much power as the master. One or more slaves can be connected to a single master, proportionally increasing power and current capability of the system.

Another application is for an input voltage to power a load, where this same input voltage is used to power a LT8708/-1 circuit that charges a battery or bank of supercapacitors. When the input voltage goes away, the load maintains power without disruption from the battery or supercaps by way of the LT8708’s bidirectional capability.

Forward and reverse current can be monitored and limited for the input and output sides of the converter. All four current limits (forward input, reverse input, forward output and reverse output) can be set independently using four resistors. In combination with the DIR (direction) pin, the chip can be configured to process power from V_IN to V_OUT or from V_OUT to V_IN ideal for automotive, solar, telecom and battery-powered systems.

The LT8708 is available in a 5mm × 8mm QFN-40 package. Three temperature grades are available, with operation from –40 to 125°C for the extended and industrial grades and a high temp automotive range of –40°C to 150°C. For more information, visit https://www.analog.com/LT8708.