The advantage of an active cell balancing is that it avoids the energy loss as occurs with passive balancing methods. The charge is transferred with a shuffle capacitor or inductor from one cell to another with nearly no losses, leading to higher efficiency and a longer battery life. In passive methods, cells of large battery stacks are balanced by discharging overcharged cells through a resistor.

In a typical battery pack, no cell is identical to another. The cells differ in the state-of-charge, self-discharge rate, cell impedance and capacity, and aging. After several charge and discharge cycles, this may result in increased voltage differences between the individual cells. This effect will impact the cells where several cells may no longer be properly charged, with the possibility of weak cells being over or undercharged. This will decrease the overall lifetime of a battery. Active balancing is a perfect method to constantly ensure that all the cells have the same state-of-charge.

“Battery efficiency and lifetime are key elements for industrial and automotive battery applications,” said Claus Mochel, Automotive High-Voltage Marketing Manager of Atmel Corporation. “Atmel’' ATA6870 addresses these issues by offering a battery management solution with a superb active balancing technique.”

Atmel's ATA6870 circuit monitors up to six battery cells and can be stacked up to 16 times. For the highest communication robustness between the stacked ICs, the IC features level shifters based on current sources. In addition, the ATA6870 includes an 8-bit checksum monitor that helps further increase data communication robustness.

The ATA6870 provides a dedicated AD converter for each battery cell to be monitored. This enables the device to simultaneously measure the voltage of all cells within one battery string for precise state-of-charge determination of Li-Ion battery cells.

Same as IC, the integrated power supply for the microcontroller can be stacked. Therefore, the current required to supply the microcontroller can be taken from the top cell and be fed back into the battery string's bottom cell. As a result, the microcontroller's current consumption will not cause any cell imbalance helping designers save expensive high-voltage devices. The on-board balancing capability can be used for various balancing techniques like passive balancing with a resistor or active balancing with a capacitor or an inductor.

Availability and Pricing

Samples of Atmel's new ATA6870 IC are now available in small QFN48 packages. Pricing starts at 2.95 US Dollars at 10k quantities.

Evaluation kits are available now to enable a quick-start with the IC to allow prototyping and testing of new battery designs immediately. Atmel also offers additional software for PCs and laptops with a graphical user interface to control and optimize high-cell-count battery stacks.

Related link: Atmel's Li-Ion battery management IC ATA6870