Datasheet

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DIGITAL FILTER

VOLTAGE

CURRENT

TEMPERATURE

GAS GAUGE OPERATION

General

bq2084-V143

SLUS732 – SEPTEMBER 2006

FUNCTIONAL DESCRIPTION (continued)

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.

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.

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.

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

INTERNAL TEMP EXTERNAL TEMP SENSOR SETTING

LOCATION

SENSOR SETTING (Semitec 103AT)

LABEL

Dec (Hex) Dec (Hex) Dec (Hex)

Misc. Config 42 (0x2a) Bit 7 = 1 Bit 7 = 0

TS Const1 A3 164/5 (0xb5/6) 0 (0x0000) –28285 (0x9183)

TS Const2 A2 166/7 (0xb7/8) 0 (0x0000) 20848 (0x5170)

TS Const3 A1 168/9 (0xb9/a) –11136 (0xd480) –7537 (0xe28f)

TS Const4 A0 170/1 (0xbb/c) 5734 (0x1666) 4012 (0x0fac)

Min Temp AD 172/3 (0xbd/e) 0 (0x0000) 0 (0x000)

Max Temp 174/5 (0xbf/c0) 5734 (0x1666) 4012 (0x0fac)

The operational overview in Figure 1 illustrates the gas gauge operation of the bq2084-V143. Table 3 describes

the bq2084-V143 registers.

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