The BQ34Z100 device accurately predicts the battery capacity and other operational characteristics of a single cell or multiple rechargeable cell blocks, which are voltage balanced when resting. The device supports various Li-ion and LiFePO₄ chemistries, and can be interrogated by a host processor to provide cell information, such as remaining capacity, full charge capacity, and average current.

Information is accessed through a series of commands called Standard Data Commands (see Section 7.2.1.1). Further capabilities are provided by the additional Extended Data Commands set (see Section 7.2.2). Both sets of commands, indicated by the general format Command(), are used to read and write information contained within the BQ34Z100 device’s control and status registers, as well as its data flash locations. Commands are sent from host to gauge using the BQ34Z100 serial communications engines, HDQ and I²C, and can be executed during application development, pack manufacture, or end-equipment operation.

Cell information is stored in the BQ34Z100 in non-volatile flash memory. Many of these data flash locations are accessible during application development and pack manufacture. They cannot, generally, be accessed directly during end-equipment operation. Access to these locations is achieved by using the BQ34Z100 device’s companion evaluation software, through individual commands, or through 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 BQ34Z100 provides 32 bytes of user-programmable data flash memory. This data space is accessed through a data flash interface. For specifics on accessing the data flash, refer to Section 7.2.3.

The key to the BQ34Z100 device’s high-accuracy gas gauging prediction is Texas Instrument’s proprietary Impedance Track algorithm. This algorithm uses voltage measurements, characteristics, and properties to create state-of-charge predictions that can achieve accuracy with as little as 1% error across a wide variety of operating conditions.

The BQ34Z100 measures charge/discharge activity by monitoring the voltage across a small-value series sense resistor connected in the low side of the battery circuit. When an application’s load is applied, cell impedance is measured by comparing its Open Circuit Voltage (OCV) with its measured voltage under loading conditions.

The BQ34Z100 can use an NTC thermistor (default is Semitec 103AT or Mitsubishi BN35-3H103FB-50) for temperature measurement, or can also be configured to use its internal temperature sensor. The BQ34Z100 uses temperature to monitor the battery-pack environment, which is used for fuel gauging and cell protection functionality.

To minimize power consumption, the BQ34Z100 has three power modes: NORMAL, SLEEP, and FULL SLEEP. The BQ34Z100 passes automatically between these modes, depending upon the occurrence of specific events.

Multiple modes are available for configuring from one to 16 LEDs as an indicator of remaining state of charge. More than four LEDs require the use of one or two inexpensive SN74HC164 shift register expanders.

A SHA-1/HMAC-based battery pack authentication feature is also implemented on the BQ34Z100. When the IC is in UNSEALED mode, authentication keys can be (re)assigned. A scratch pad area is used to receive challenge information from a host and to export SHA-1/HMAC encrypted responses. See Section 7.2.14.1 for further details.