BQ2084-V133 Datasheet, PDF (8/64 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE FOR USE WITH THE bq29312

bq2084-V133
SLUS640A – JUNE 2005 – REVISED JUNE 2005
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FUNCTIONAL DESCRIPTION (continued)
MEASUREMENTS
The bq2084-V133 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 0.25 V.
The bq2084-V133 detects charge activity when VSR = V_(SR1)-V_(SR2) is positive and discharge activity when VSR
= V(SR1)-V(SR2) is negative. The bq2084-V133 continuously integrates the signal over time, using an internal
counter. The fundamental rate of the counter is 0.65 nVh. The bq2084-V133 updates RemainingCapacity() with
the charge or discharge accumulated in this internal counter once every second.
OFFSET CALIBRATION
The bq2084-V133 provides an auto-calibration feature to cancel the voltage offset error across SR1 and SR2 for
maximum charge measurement accuracy. The bq2084-V133 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-V133 is capable of automatic offset calibration down to <1 µV.
DIGITAL FILTER
The bq2084-V133 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-V133 monitors the individual
series cell voltages through the bq29312. The bq2084-V133 configures the bq29312 to present the selected cell
to the CELL pin of the bq29312, which should be connected to VIN of the bq2084-V133. The internal ADC of the
bq2084-V133 then measures the voltage and scales it appropriately. The bq2084-V133 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-V133 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-V133 along with an NTC thermistor measures the battery temperature as shown in
the schematic. The bq2084-V133 reports temperature via the SBS command Temperature().
The bq2084-V133 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.
LABEL
Misc. Config
TS Const1 A3
Table 1. Data Flash Settings for Internal or External Temperature Sensor
LOCATION
Dec (Hex)
42 (0x2a)
164/5 (0xb5/6)
INTERNAL TEMP
SENSOR SETTING
Dec (Hex)
Bit 7 = 1
0 (0x0000)
EXTERNAL TEMP SENSOR SETTING
(Semitec 103AT)
Dec (Hex)
Bit 7 = 0
–28285 (0x9183)
8