Bi-directional buck-boost controller addresses redundancy in autonomous cars

A 98 per cent efficient bi-directional buck-boost switching regulator controller from Analog Devices operates between two batteries that have the same voltage, making it suitable for redundancy in self-driving cars. The Power by Linear LT8708 and LT8708-1 regulator operates from an input voltage that can be above, below or equal to the output voltage. The regulator operates between two batteries and prevents system shut-down should one of the batteries fail. It is suitable for two each 12, 24 or 48V batteries commonly found in electric and hybrid vehicles. The LT8708/ LT8708-1 can also be used in 48/12V and 48/24V dual battery systems.

The regulator operates with a single inductor over a 2.8 to 80V input voltage range and can produce an output voltage from 1.3 to 80V, delivering up to several kilowatts of power, depending on the choice of external components and number of phases, advises Analog Devices. It is claimed to simplify bi-directional power conversion in battery/capacitor back-up systems that need regulation of VOUT, VIN, and/or IOUT, IIN, both in the forward or reverse direction. There are six independent forms of regulation allowing the regulator to be used in various applications, from electric and hybrid vehicles to solar and telecomms systems.

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, and 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, the load maintains power without disruption from the battery or supercapacitors by way of the LT8708’s bi-directional 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 direction pin, the chip can be configured to process power from VIN to VOUT or from VOUT to VIN for automotive, solar, telecomms and battery-powered systems.

The LT8708 is available in a 5.0 x 8.0mm QFN-40 package. Three temperature grades are available, operating from -40 to +125 degree C for the extended and industrial grades and a high temperature automotive range of -40 to +150 degrees C.

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