A high efficiency bidirectional multicell battery balancer has been released by Linear Technology Corporation for equalizing cell state of charge (SoC) in a series-connected battery stack.

The company advises, with the LTC3300-1, applications such as electric vehicles (EVs), plug-in hybrid EVs and large energy storage systems using cells with mismatched capacities are no longer limited by the lowest capacity cell in the stack.

This device is said to be capable of more than the currently available dissipative passive balancing solutions, enhancing battery performance by efficiently transferring charge to or from adjacent cells in order to bring mismatched cells into SoC balance within the stack. 

By redistributing charge throughout the stack, this device is able to compensates for lost capacity due to the weakest cells, enabling faster charging and extending the run time and usable lifetime of the battery stack.  

The device is described as operating as a fault-protected controller IC for transformer-based bidirectional active balancing. The part utilises a nonisolated bidirectional synchronous flyback topology to balance up to 6 series-connected cells.   Charge can be transferred between a selected cell and 12 or more adjacent cells.   All balancers can operate independently and simultaneously with charge/discharge currents up to 10A.  

Bidirectional operation and simultaneous balancing minimises the time required to equalize stack SoC, and the parts’ high transfer efficiency (up to 92 percent) is said to enable high current balancing with minimal power dissipation.

An interesting feature of the device is that, control of each balancer is provided via a level-shifting SPI-compatible serial interface, which enables multiples of these devices to be connected in series, without optocouplers or isolators.  

As a result of the clever stackable architecture of the device, together with interleaved transformer connections this enables efficient balancing of every cell in an arbitrarily tall string (>1000V) of series-connected batteries. 

Further benefits include the fact that, all associated gate drive circuitry, precision current sensing, fault protection circuitry and a robust serial data interface with built-in watchdog timer and cyclic redundancy check (CRC) data error checking are integrated.

This device is offered in thermally enhanced surface-mount compatible packages: a low profile (0.75mm) 48-lead 7mm by 7mm QFN and a 48-pin 7mm by 7mm LQFP package.

The I grade is specified for both packages, with operating junction temperature range of -40°C to 125°C.

Linear Technology Corporation