bq40z60 system block diagram
Managing a rechargeable lithium-ion battery could range from simple protection features built-in to the cell to extensive external-pack-level management. While designed-in cell-level safety measures are a must-have, a smart battery calls for a comprehensive multilevel management system.
In broad terms, these comprehensive features/abilities include battery charging, accurate cell measurements, battery safety, cell balancing, battery capacity and health indication, diagnostic data collection, and security. The ultimate goal of a battery-management unit is to safely extend battery run time and life.
Safety is a key aspect of comprehensive management. Rechargeable batteries are made from reactive chemicals that provide the higher-energy-density demands of today’s portable devices. A multicellular battery pack holds as much energy as a hand grenade and has the potential for thermal runaway. Consequently, you need multiple independent levels of robust protection covering voltage, current and temperature.
Lithium-ion batteries follow a constant current, constant voltage (CCCV) charging profile. During constant current (CC) mode, the charger should be capable of holding the current constant both while the battery voltage increases and once the voltage reaches its maximum charging voltage (typically 4.1V or 4.2V). The charger should also be capable of moving to constant voltage (CV) mode, keeping the voltage constant and reducing current to reach taper termination. Charging the battery within limits set by the cell manufacturer and avoiding overcharging is important.
Battery gauging involves accurately predicting the battery’s state of charge (SOC) and state of health (SOH). Best-in-class gauging algorithms, like TI’s Impedance Track™ technology are capable of accurately predicting the SOC/SOH of a battery pack at various ranges of discharge current profiles – both over the end equipment’s entire operating temperature range and throughout the battery’s lifecycle, including when it is old and battery resistance has increased dramatically.
Battery-pack cells are not identical and typically have slight variations in their capacity and impedance characteristics. These variations lead to a divergence in cell voltages over time. The job of the cell balancer is to equalize the voltage and SOC of series-connected cells when they reach full charge. Cell balancing prevents cell degradation and ensures that the end application can use the battery pack’s full available capacity.
Diagnostic data collection refers to the battery management unit’s ability to track and record a variety of usage information about the battery. End-equipment/battery-pack manufacturers can then use this data to review battery warranty claims and ensure that the pack was used within the application’s specified limits.
Last but not least, after carefully designing the battery pack for the end application’s needs, you don’t want a poorly designed knockoff to compromise your brand image. This is where built-in authentication comes in handy; without any additional cost, you can protect your design from cheap imitation. Built-in authentication has the authentication engine such as SHA-1 integrated in the device and allows only the specific battery pack with the correct embedded authentication information to pair with the system.
I’ve given a very brief overview of the different elements that make up a comprehensive battery manager. What if one single device could be all things battery? The bq40Z60 is a battery management unit that integrates charging, gauging, protection and authentication in a single, compact, quad flat no-lead (QFN) package capable of managing two- to four-series lithium-ion packs. Take advantage of this industry-first device with its configurable features to meet your system-specific needs.
To learn more about TI’s battery-management portfolio, see ti.com/battery.
