Figure 4 LTC3300 high efficiency bidirectional multicell active balancer. For full resolution click here .
SoC balance is achieved by redistributing charge between a selected cell and a sub-stack of up to 12 or more adjacent cells. The balancing decisions and balancing algorithms must be handled by a separate monitoring device and system processor that controls the LTC3300. Charge is redistributed from a selected cell to a group of 12 or more neighboring cells in order to discharge the cell. Similarly, charge is transferred to a selected cell from a group of 12 or more neighbor cells in order to charge the cell. All balancers may operate simultaneously, in either direction, to minimize stack balancing time. All balancing control commands are delivered to each IC via a stackable, high noise margin serial SPI interface with no limit on the height of the stack.
Each balancer in the LTC3300 uses a nonisolated, boundary mode synchronous flyback power stage to achieve high efficiency charging and discharging of each individual cell (see Figure 5). Each of the six balancers requires its own transformer. The “primary” side of each transformer is connected across the cell to be balanced, and the “secondary” side is connected across 12 or more adjacent cells – including the cell to be balanced. The number of cells on the secondary side is limited only by the breakdown voltage of the external components.
Figure 5 Bidirectional flyback power stage operation. For full resolution click here .
Cell charge and discharge currents are programmed by external sense resistors to values as high as 10+ amps with corresponding scaling of the