BQ2084DBTR-V150 Datasheet, PDF (8/69 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE WITH LED DELAY

bq2084-V150
SLUS758 – JUNE 2007
www.ti.com
RSOC (pin 33) and VSSA (pin 34). It is recommended that this resistor be as close to the bq2084-V150 as
possible and that it has a specification of ±0.1% tolerance and ±50 ppm temperature drift or better. The 12-pF
crystal, if used, should also be placed as close to the XCK1 (pin 34) and XCK2 (pin 33) pins as possible. The
layout of the PCB around these pins and components is also an additional contributing factor to oscillator
performance degradation.
The average temperature drift error of the oscillator function over a learning charge or discharge cycle
introduces an equal capacity prediction error in a learned full charge capacity (FCC).
SYSTEM PRESENT OPERATION
When the bq2084-V150 detects that the battery is inserted into the system via a low state on the PRES input,
the bq2084-V150 enters normal operating mode and sets the PRES bit in PackStatus(). The discharge FET
turns on within 250 ms of pack insertion. When the pack is removed from the system and the PRES input is
high, then the bq2084-V150 enters the battery removed state and turns OFF the charge and discharge FETs,
and enables the 0-V/precharging FET. If NR in Misc Config is set, then the PRES input can be left floating as it
is not used.
GENERAL OPERATION
The bq2084-V150 determines battery capacity by monitoring the amount of charge input or removed from a
rechargeable battery. In addition to measuring charge and discharge, the bq2084-V150 measures individual cell
voltages, pack voltage, temperature, and current, estimates battery self-discharge, and monitors the battery for
low-voltage thresholds using features of the bq29312A AFE device.
The bq2084-V150 measures charge and discharge activity by monitoring the voltage across a small-value series
sense resistor between the cell stack negative terminal and the negative terminal of the battery pack. The
available battery charge is determined by monitoring this voltage and correcting the measurement for
environmental and operating conditions.
The bq2084-V150 interfaces with the bq29312A to perform battery protection, cell balancing, and voltage
translation functions. The bq2084-V150 can accept any NTC thermistor (default is Semitec 103AT) for
temperature measurement or can also be configured to use its internal temperature sensor. The bq2084-V150
uses temperature to monitor the battery pack and to compensate the self-discharge estimate.
MEASUREMENTS
The bq2084-V150 uses an integrating sigma-delta analog-to-digital converter (ADC) for current measurement
and a second sigma-delta ADC for individual cell and battery voltage and temperature measurement. The
individual cell and pack voltages, Voltage(), Current(), AverageCurrent() and Temperature() are updated every 1
s during normal operation.
CHARGE AND DISCHARGE COUNTING
The integrating ADC measures the charge and discharge flow of the battery by monitoring a small-value sense
resistor between the SR1 and SR2 pins. The integrating ADC measures bipolar signals from -0.25 V to 0.25μV.
The bq2084-V150 detects charge activity when VSR = V(SR1)-V(SR2) is positive and discharge activity when
VSR = V(SR1)-V(SR2) is negative. The bq2084-V150 continuously integrates the signal over time, using an
internal counter. The fundamental rate of the counter is 0.65 nVh. The bq2084-V150 updates
RemainingCapacity() with the charge or discharge accumulated in this internal counter once every second.
OFFSET CALIBRATION
The bq2084-V150 provides an auto-calibration feature to cancel the voltage offset error across SR1 and SR2 for
maximum charge measurement accuracy. The bq2084-V150 performs auto-calibration when the SMBus lines
stay low for a minimum of 20 s when it internally connects SR1 to SR2 and measures the internal offset. With
this feature the bq2084-V150 is capable of automatic offset calibration down to <1 µV.
DIGITAL FILTER
The bq2084-V150 does not measure charge or discharge counts below the digital filter threshold. The digital
filter threshold is programmed in the Digital Filter DF 0x2c and should be set sufficiently high to prevent false
signal detection with no charge or discharge flowing through the sense resistor.
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