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SLUS732 – SEPTEMBER 2006
FUNCTIONAL DESCRIPTION (continued)
DIGITAL FILTER
The bq2084-V143 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-V143 monitors the individual
series cell voltages through the bq29312. The bq2084-V143 configures the bq29312 to present the selected cell
to the CELL pin of the bq29312, which should be connected to VIN of the bq2084-V143. The internal ADC of the
bq2084-V143 then measures the voltage and scales it appropriately. The bq2084-V143 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-V143 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-V143 along with an NTC thermistor measures the battery temperature as shown in
the schematic. The bq2084-V143 reports temperature via the SBS command
Temperature().
The bq2084-V143 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.
Table 1. Data Flash Settings for Internal or External Temperature Sensor
LABEL
Misc. Config
TS Const1 A3
TS Const2 A2
TS Const3 A1
TS Const4 A0
Min Temp AD
Max Temp
LOCATION
Dec (Hex)
42 (0x2a)
164/5 (0xb5/6)
166/7 (0xb7/8)
168/9 (0xb9/a)
170/1 (0xbb/c)
172/3 (0xbd/e)
174/5 (0xbf/c0)
INTERNAL TEMP
SENSOR SETTING
Dec (Hex)
Bit 7 = 1
0 (0x0000)
0 (0x0000)
–11136 (0xd480)
5734 (0x1666)
0 (0x0000)
5734 (0x1666)
EXTERNAL TEMP SENSOR SETTING
(Semitec 103AT)
Dec (Hex)
Bit 7 = 0
–28285 (0x9183)
20848 (0x5170)
–7537 (0xe28f)
4012 (0x0fac)
0 (0x000)
4012 (0x0fac)
GAS GAUGE OPERATION
General
The operational overview in
illustrates the gas gauge operation of the bq2084-V143.
describes
the bq2084-V143 registers.
9
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