BQ28Z560-R1 Datasheet, PDF (12/60 Pages) Texas Instruments – Single Cell Li-Ion Battery Gas Gauge and Protection

bq28z560-R1
SLUSBD3 – APRIL 2013
GENERAL DESCRIPTION
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The bq28z560-R1 accurately predicts the battery capacity and other operational characteristics of a single Li-Ion
based rechargeable cell, while also providing a state-of-the-art protection function against short circuit,
overcurrent, and overvoltage. The device can be integrated by a system processor to provide cell information,
such as state-of-charge (SOC), Remaining Capacity, and Full Charge Capacity (FCC).
NOTE
FORMATTING CONVENTIONS IN THIS DOCUMENT:
Commands: Italics with parentheses and no breaking spaces; for example,
RemainingCapacity()
Data Flash: Italics, bold, and breaking spaces; for example, Design Capacity
Register Bits and Flags: Brackets only; for example, [TDA]
Data Flash Bits: Italics and bold; for example, [NR]
Modes and States: All capitals; for example, SEALED mode
DATA ACQUISITION
Cell Voltage
The bq28z560-R1 samples the single cell voltage from the BAT input terminal. The cell voltage is sampled and
updated every 1 s in NORMAL mode. To ensure accurate cell measurement, the VSS ground connection of the
bq28z560-R1 should be connected to the negative terminal of the single cell and not to the positive side of the
sense resistor.
Charge Measurement
The device samples the charge into and out of the single cell using a low-value sense resistor. The resistor
(typically 5 mΩ to 20 mΩ) is connected between SRP and SRN to form a differential input to an integrating ADC
(coulomb counter). Charge activity is detected when V_SR = V_SRP – V_SRN is positive and discharge activity is
detected when V_SR = V_SRP – V_SRN is negative. This data is integrated over a period of time using an internal
counter, and updates RemainingCapacity with charge and discharge amounts every 1 s in NORMAL mode.
Current Measurement
The device has a FIFO buffer, which uses the last four coulomb counter readings to calculate the current. The
current is updated every 1 s in NORMAL mode.
CELL DETECTION
Internal Short Detection
The device can detect an internal battery short by setting the [SE_ISD] bit in Pack Configuration Register B. The
bq28z560-R1 compares the self-discharge current calculated based on StateOfCharge() in RELAX mode and
AverageCurrent() measured in the system. The self-discharge is measured at 1-hour intervals. When the battery
SelfDischargeCurrent() is less than a predefined ISD Current threshold, the ISD flag bit is set high.
Tab Disconnection Detection
The bq28z560-R1 detects tab disconnection by change in StateOfHealth(). This feature is enabled by setting the
[SE_TDD] bit in Pack Configuration Register B. The [TDD] bit is set in the flag register when the ratio of current
StateOfHealth() divided by the previous StateOfHealth() reported is less than TDD SOH percent.
TEMPERATURE MEASUREMENT AND THE TS INPUT
The bq28z560-R1 measures external temperature via the TS pin in order to supply battery temperature status
information to the gas gauging algorithm and charger-control sections of the gauge. Alternatively, the gauge can
also measure internal temperature via its on-chip temperature sensor. Refer to the Pack Configuration[TEMPS]
control bit.
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