Fig 1. bq34z110 is a scalable power management device that supports multi-cell lead-acid battery packs.

The bq34z110 gas gauge IC from Texas Instruments provides accurate operating data for lead- acid batteries, a capability not available from other sources. This 14-pin IC (Fig. 1) is the industry’s only scalable gas gauge device that supports multi-cell lead-acid battery packs with battery voltages of 4 V, 12 V, 24 V, 48 V and higher.

Until recently, it has been difficult to accurately measure and report a lead-acid battery’s current capacity. This could frustrate the end user, and require more batteries to ensure an adequate output load. The bq34z110 solves this problem by employing T.I.’s proprietary Impedance Track algorithm that uses voltage, current, temperature measurements, and battery characteristics, to assess battery state-of-charge within 1% error over normal operating conditions.

Fig 2. Typical implementation of bq34z110 for lead-acid battery.

Fig. 2 shows a typical bq34z110 circuit implementation. The bq34z110 gauge continuously informs the user about a lead-acid battery’s state-of-health and state-of-charge and maintains up to a 95-percent accurate capacity measurement for the battery’s entire life. This information prevenqts premature shutdown and increases longevity of the battery and end equipment. An associated host processor can interrogate the gas gauge to obtain cell information, such as remaining capacity, full charge capacity, and average current. Table 1 lists the recommended operating conditions.

Standard Commands in the bq34z110 access battery information, with additional capabilities provided by an Extended Commands set. Both sets of commands are used to read and write information contained within the IC’s control and status registers, as well as its data flash locations. Commands are sent from the host to the fuel gauge IC using HDQ or I2C serial communications engines that can execute during application development, pack manufacture, or end-equipment operation.

The 2-byte Standard Commands consist of two data bytes. Two consecutive HDQ or I2C transmissions must be executed to initiate the command function and to read or write the corresponding two bytes of data. Also, two block commands are available to read the manufacturer name and device chemistry.

Also included in the bq34z110 are 32 bytes of user-programmable, non-volatile data flash memory, accessible via its data flash interface. The data flash memory contains initialization, default, cell status, calibration, configuration, and user information. Cell information is stored in this 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 either use of companion evaluation software, through individual commands, or through a sequence of data-flash-access commands.

Most data flash locations, however, can only accessible in UNSEALED mode by use of the evaluation software or by data flash block transfers. These locations should be optimized and/or fixed during the development and manufacture processes. They become part of a Golden Image File and can then be written to multiple battery packs. Once established, the values generally remain unchanged or get updated by the gauge algorithm during end equipment operation.

Two security modes control data flash access permissions:

•Public Access refers to those data flash locations that are accessible to the user.

•Private Access refers to reserved data flash locations used by the bq34z110.