BQ27520YZFR-G4 Datasheet, PDF (8/19 Pages) Texas Instruments – System-Side Impedance Track Fuel Gauge With Integrated LDO

bq27520-G4
SLUSB20 – NOVEMBER 2012
GENERAL DESCRIPTION
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The bq27520-G4 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 time-
to-empty (TTE) and state-of-charge (SOC) as well as SOC interrupt signal to the host.
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 contained within the device control and status registers, as
well as its data flash locations. Commands are sent from system to gauge using the bq27520-G4 ’s I²C serial
communications engine, and can be executed during application development, system manufacture, or end-
equipment operation.
Cell information is stored in the device 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. Access to these locations is achieved by either use of the bq27520-G4 ’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 key to the bq27520-G4 ’s 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 device measures charge/discharge activity by monitoring the voltage across a small-value series sense
resistor (5 mΩ to 20 mΩ typ.) located between the system’s Vss and the battery’s PACK- terminal. When a cell is
attached to the device, cell impedance is learned, based on cell current, cell open-circuit voltage (OCV), and cell
voltage under loading conditions.
The device external temperature sensing is optimized with the use of a high accuracy negative temperature
coefficient (NTC) thermistor with R25 = 10.0kΩ ±1%. B25/85 = 3435K ± 1% (such as Semitec NTC 103AT).
Alternatively, the bq27520-G4 can also be configured to use its internal temperature sensor or receive
temperature data from the host processor. When an external thermistor is used, a 18.2k pull up resistor between
BI/TOUT and TS pins is also required. The bq27520-G4 uses temperature to monitor the battery-pack
environment, which is used for fuel gauging and cell protection functionality.
To minimize power consumption, the device has different power modes: NORMAL, SLEEP+, SLEEP,
HIBERNATE, and BAT INSERT CHECK. The bq27520-G4 passes automatically between these modes,
depending upon the occurrence of specific events, though a system processor can initiate some of these modes
directly.
For complete operational details, refer to bq27520-G4 Technical Reference Manual.
NOTE
FORMATTING CONVENTIONS IN THIS DOCUMENT:
Commands: italics with parentheses and no breaking spaces, e.g. RemainingCapacity( ).
NVM Data: italics, bold, and breaking spaces, e.g. Design Capacity.
Register bits and flags: brackets and italics, e.g. [TDA]
NVM Data bits: brackets, italics and bold, e.g: [LED1]
Modes and states: ALL CAPITALS, e.g. UNSEALED mode.
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