BQ27520-G2 Datasheet, PDF (9/47 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated LDO

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bq27520-G2
SLUSAB7A – MARCH 2011 – REVISED AUGUST 2011
4 GENERAL DESCRIPTION
The bq27520-G2 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), time-to-full (TTF) 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-G2’s I²C serial communications engine, and can be executed during application development,
pack 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-G2’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 bq27520-G2 provides a 32-byte user-programmable data flash Manufacturer Info Block. This data
space is accessed through a data flash interface. For specifics on accessing the data flash,
see Section 4.3: MANUFACTURER INFORMATION BLOCKS.
The key to the bq27520-G2’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 computed, 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-G2 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 BT/TOUT and TS pins is also required. The bq27520-G2 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-G2 passes automatically between these modes,
depending upon the occurrence of specific events, though a system processor can initiate some of these
modes directly. More details can be found in
see 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 and italics, e.g., [TDA]
Data flash bits: brackets, italics and bold, e.g., [LED1]
Modes and states: ALL CAPITALS, e.g., UNSEALED mode.
Copyright © 2011, Texas Instruments Incorporated
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GENERAL DESCRIPTION
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