Bi-directional buck-boost controller balances self-driving vehicle batteries
Two batteries with the same voltage can be balanced using the LT8708/LT8708-1 bi-directional buck-boost switching regulator from Analog Devices. The Power by Linear regulator is 98 per cent efficient regulator controller operates from an input voltage that can be above, below or equal to the output voltage. This makes it suitable for two 12V, 24V or 48V batteries commonly found in electric and hybrid vehicles (EVs and HEVs).
The controller operates between two batteries and prevents system shut-down should one of the batteries fail.
The LT8708/-1 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, depending on the choice of external components and number of phases. It simplifies bi-directional power conversion in battery/capacitor backup systems that need regulation of VOUT, VIN, and/or IOUT, IIN, both in the forward or reverse direction. The six independent forms of regulation allow it to be used in numerous applications, says Analog Devices.
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.
The controller can also be used as an input voltage to power a load, where the 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 supercapacitors 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 direction pin, the chip can be configured to process power from VIN to VOUT or from VOUT to VIN ideal 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, with operation from -40 to +125 degree C for the extended and industrial grades and a high temperature automotive range of -40 to +150 degree C.