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bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
The bq27500/1 accurately predicts the battery capacity and other operational characteristics of a singleLi-based rechargeable cell. It can be interrogated by a system processor to provide cell information, suchas State-of-Charge (SOC), Time-to-Empty (TTE) and Time-to-Full (TTF).
Information is accessed through a series of commands, called Standard Commands. Further capabilitiesare provided by the additional Extended Commands set. Both sets of commands, indicated by the generalformat Command( ), are used to read and write information contained within the bq27500/1 control andstatus registers, as well as its data flash locations. Commands are sent from system to gauge using thebq27500/1’s I
2
C serial communications engine, and can be executed during application development,pack manufacture, or end-equipment operation.
Cell information is stored in the bq27500/1 in non-volatile flash memory. Many of these data flashlocations are accessible during application development. They cannot be accessed directly duringend-equipment operation. Access to these locations is achieved by either use of the bq27500/1'scompanion evaluation software, through individual commands, or through a sequence of data-flash-accesscommands. To access a desired data flash location, the correct data flash subclass and offset must beknown.
The bq27500/1 provides 96 bytes of user-programmable data flash memory, partitioned into 3 32-byteblocks: Manufacturer Info Block A,Manufacturer Info Block B, and Manufacturer Info Block C. Thisdata space is accessed through a data flash interface. For specifics on accessing the data flash, seeSection 4.3 Manufacturer Information Blocks.
The key to the bq27500/1’s high-accuracy gas gauging prediction is Texas Instrument’s proprietaryImpedance Track™ algorithm. This algorithm uses cell measurements, characteristics, and properties tocreate state-of-charge predictions that can achieve less than 1% error across a wide variety of operatingconditions and over the lifetime of the battery.
The bq27500/1 measures charge/discharge activity by monitoring the voltage across a small-value seriessense resistor (5 m Ωto 20 m Ωtyp.) located between the system's Vss and the battery’s PACK– terminal.When a cell is attached to the bq27500/1, cell impedance is computed, based on cell current, cell OpenCircuit Voltage (OCV), and cell voltage under loading conditions.
The bq27500/1 can use an NTC thermistor (default is Semitec 103AT) for temperature measurement, orcan also be configured to use its internal temperature sensor. The bq27500/1 uses temperature to monitorthe battery-pack environment, which is used for fuel gauging and cell protection functionality.
To minimize power consumption, the bq27500/1 has several power modes: NORMAL, SLEEP,HIBERNATE, and BAT INSERT CHECK. The bq27500/1 passes automatically between these modes,depending upon the occurrence of specific events, though a system processor can initiate some of thesemodes directly. More details can be found in the Section 5.7 POWER MODES.
NOTE
FORMATTING CONVENTIONS IN THIS DOCUMENT:
Commands: italics with parentheses and no breaking spaces, e.g. RemainingCapacity( ).
Data Flash: italics,bold, and breaking spaces, e.g. Design Capacity
Register Bits and Flags: brackets only, e.g. [TDA]
Data Flash Bits: italics and bold, e.g: [LED1]
Modes and states: ALL CAPITALS, e.g. UNSEALED mode.
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