Multi-kW bi-directional dc-dc converter is 98% efficient for e-vehicles

Analog Devices has announced multi-phase 98% efficient bi-directional buck-boost switching regulator controllers, which can mediate between any combination of 12, 24 and 48V batteries.

Intended for cars, self-driving cars, for example, the LT8708-1 “operates between two batteries and prevents system shut-down should one of the batteries fail,” said the firm. “It can also be used in 48V/12V and 48V/24V dual battery systems.”

It operates with a single inductor, over a 2.8-80V on the nominal input (but a >6.4V auxiliary supply is required), producing 1.3-80V on the nominal output, “delivering up to several kilowatts of power depending on the choice of external components and number of phases”, said the firm.

Each phase needs its own chip, mosfets and inductor.

When only a single phase is required, the original LT8708 is the right answer, while the LT8708 -1 comes into play, with its associated mosfets and inductor, when a two-or-more-phase converter is needed.

“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 current capability of the system,” said ADI. “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.”

Six forms of regulation are possible: Vout, Vin, In (forward and reverse), and Iout (forward and reverse).

Forward and reverse current are separately 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, and both forward and reverse discontinuous conduction operation is possible.

The chip comes in a 5 x 8 QFN-40, and is available in -40 to 125°C, or for automotive use -40°C to 150°C.