bq27520-G4

SLUSB20 – NOVEMBER 2012

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GENERAL DESCRIPTION

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

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 m

Ω 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 = 10.0k

Ω ±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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