8.1 Overview

The bq27545-G1 accurately predicts the battery capacity and other operational characteristics of a single Li-based rechargeable cell. It can be interrogated by a system processor to provide cell information, such as state-of-charge (SOC) and time-to-empty (TTE).

Information is accessed through a series of commands, called Standard Commands. Further capabilities are provided by the additional Extended Commands set. Both sets of commands, indicated by the general format Command(), are used to read and write information in the bq27545-G1 control and status registers, as well as its data flash locations. Commands are sent from the system to the gauge using the bq27545-G1 serial communications engine, and can be executed during application development, pack manufacture, or end-equipment operation.

Cell information is stored in the bq27545-G1 in non-volatile flash memory. Many of these data flash locations are accessible during application development. They cannot, generally, be accessed directly during end-equipment operation. To access to these locations, use the bq27546-G1 companion evaluation software, individual commands, or a sequence of data-flash-access commands. To access a desired data flash location, the correct data flash Subclass and offset must be known.

The bq27545-G1 provides 64 bytes of user-programmable data flash memory, partitioned into two (2) 32-byte blocks: Manufacturer Info Block A and Manufacturer Info Block B. This data space is accessed through a data flash interface. For specific details on accessing the data flash, see Manufacturer Information Blocks. The key to the bq27545-G1 high-accuracy gas gauging prediction is Texas Instrument’s proprietary Impedance Track algorithm. This algorithm uses cell measurements, characteristics, and properties to create state-of-charge predictions that can achieve less than 1% error across a wide variety of operating conditions and over the lifetime of the battery.

The bq27545-G1 measures charge/discharge activity by monitoring the voltage across a small-value series sense resistor (5 mΩ to 20 mΩ typical) located between the CELL– and the battery’s PACK– terminal. When a cell is attached to the bq27545-G1, cell impedance is learned based on cell current, cell open-circuit voltage (OCV), and cell voltage under loading conditions.

The bq27545-G1 external temperature sensing is optimized with the use of a high accuracy negative temperature coefficient (NTC) thermistor with R25 = 10 kΩ ± 1% and B25/85 = 3435 K ± 1% (such as Semitec 103AT) for measurement. The bq27545-G1 can also be configured to use its internal temperature sensor. The bq27545-G1 uses temperature to monitor the battery-pack environment, which is used for fuel gauging and cell protection functionality.

To minimize power consumption, the bq27545-G1 has different power modes: NORMAL, SLEEP, FULLSLEEP, and HIBERNATE. The bq27545-G1 passes automatically between these modes, depending upon the occurrence of specific events, though a system processor can initiate some of these modes directly. Power Modes has more details.