BQ2084-V140_14 Datasheet, PDF (8/64 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE FOR USE WITH THE bq29312

bq2084-V140
SLUS664B – JULY 2005 – REVISED AUGUST 2006
www.ti.com
FUNCTIONAL DESCRIPTION (continued)
The bq2084-V140 interfaces with the bq29312 to perform battery protection, cell balancing, and voltage
translation functions. The bq2084-V140 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-V140
uses temperature to monitor the battery pack and to compensate the self-discharge estimate.
MEASUREMENTS
The bq2084-V140 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-V140 detects charge activity when VSR = V(SR1)-V(SR2) is positive and discharge activity when
VSR = V(SR1)-V(SR2) is negative. The bq2084-V140 continuously integrates the signal over time, using an
internal counter. The fundamental rate of the counter is 0.65 nVh. The bq2084-V140 updates
RemainingCapacity() with the charge or discharge accumulated in this internal counter once every second.
OFFSET CALIBRATION
The bq2084-V140 provides an auto-calibration feature to cancel the voltage offset error across SR1 and SR2 for
maximum charge measurement accuracy. The bq2084-V140 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-V140 is capable of automatic offset calibration down to <1 µV.
DIGITAL FILTER
The bq2084-V140 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.
VOLTAGE
While monitoring SR1 and SR2 for charge and discharge currents, the bq2084-V140 monitors the individual
series cell voltages through the bq29312. The bq2084-V140 configures the bq29312 to present the selected cell
to the CELL pin of the bq29312, which should be connected to VIN of the bq2084-V140. The internal ADC of the
bq2084-V140 then measures the voltage and scales it appropriately. The bq2084-V140 then reports the
Voltage() and the individual cell voltages in VCELL1(), VCELL2(), VCELL3(), and VCELL4(). An additional
SMBus command (0x45) returns the measured ADC Reading of the PACK input to the AFE.
CURRENT
The bq2084-V140 uses the SR1 and SR2 inputs to measure and calculate the battery charge and discharge
current. This value is reported via the SBS command Current(). AverageCurrent() is implemented as a
single-pole IIR filter with a 14.5-s time constant.
TEMPERATURE
The TS input of the bq2084-V140 along with an NTC thermistor measures the battery temperature as shown in
the schematic. The bq2084-V140 reports temperature via the SBS command Temperature().
The bq2084-V140 can also be configured to use its internal temperature sensor by setting the IT bit in Misc
Configuration DF 0x2a-0x2b. Data flash locations DF 0xb5 through DF 0xc0 also have to be changed to
prescribed values if the internal temperature sensor option is selected.
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