A battery pack is only as useful as the individual cells inside it allow. As cells age and move through repeated charge and discharge cycles, differences in their voltage and capacity can limit how much energy the entire pack is able to use.
STMicroelectronics is targeting this problem with the L9962, a new battery-management IC for lithium-ion and lithium-polymer packs containing up to 10 series-connected cells. The device combines cell monitoring, balancing and protection functions for applications ranging from cordless power tools and medical equipment to e-bikes, scooters and uninterruptible power supplies.
At the center of the L9962 is a 12-bit ADC that continuously measures individual cell voltages. Engineers can program the measurement loop time, while the IC monitors for overvoltage and undervoltage conditions and checks the measured stack voltage against the expected voltage for the number of cells in the pack.
When cells begin to drift apart, the device provides up to 70mA of balancing current to bring their voltages back into alignment. Faster balancing becomes useful as cell counts and capacities increase because the battery-management system has less time to spend correcting differences between cells during normal operation.
The L9962 also integrates a current-sense amplifier for measuring charge and discharge current through Coulomb counting. ST specifies 0.25% current-measurement accuracy across the device’s full operating-temperature range after a single-point production calibration. The IC monitors excessive charge and discharge current and provides short-circuit discharge protection.
Temperature is monitored using an external NTC thermistor, allowing the battery-management system to detect pack over-temperature and under-temperature conditions.
ST has also folded several supporting battery-pack functions into the device. These include fuse management, configurable high-side and low-side pre-drivers for pack relays and a 3.3V low-dropout regulator. The LDO remains active during standby, providing power for external circuitry such as a microcontroller or indicator LEDs without requiring a separate supply.
For equipment that spends significant time idle or in storage, the L9962 draws 5µA in standby and 2µA in deep-sleep mode. Those figures are particularly relevant for products that may sit in a warehouse, remain in transit or spend long periods between uses.
An I2C interface connects the L9962 to a host controller, which can configure parameters including the voltage-measurement interval and retrieve battery information including state of charge and state of health.
The L9962 is designed for four- to 10-cell battery packs, putting it in a range suited to portable equipment and smaller electrified systems where designers need accurate monitoring without building the battery-management system from a larger collection of discrete components.
STMicroelectronics says the L9962 is in production now in a 7mm × 7mm, 48-pin TQFP package. Pricing starts at $2.89 in quantities of 1,000.
