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BQ2085 Datasheet(PDF) 8 Page - Texas Instruments |
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BQ2085 Datasheet(HTML) 8 Page - Texas Instruments |
8 / 56 page bq2085 SLUS541 – OCTOBER 2002 8 www.ti.com Measurements The bq2085 uses an integrating sigma-delta analog-to-digital converter (ADC) for current measurement and a second sigma delta ADC for battery voltage and temperature measurement. Voltage, current, and temperature measurements are made every second. 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 as shown in the schematic. The integrating ADC measures bipolar signals from –0.3 to 1.0 V. The bq2085 detects charge activity when VSR = V(SR1)–V(SR2) is positive and discharge activity when VSR = V(SR1)–V(SR2) is negative. The bq2085 continuously integrates the signal over time, using an internal counter. The fundamental rate of the counter is 2.6 nVh. The bq2085 updates Remaining Capacity( ) with the charge or discharge accumulated in this internal counter once every second. Offset Calibration The bq2085 provides an autocalibration feature to cancel the voltage offset error across SR1 and SR2 for maximum charge measurement accuracy. The bq2085 performs autocalibration when the SMBus lines stay low for a minimum of 20 s. The bq2085 is capable of automatic offset calibration down to 1 µV. Digital Filter The bq2085 does not measure charge or discharge counts below the digital filter threshold. The digital filter threshold is programmed in the Digital Filter DF 0x2b 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 bq2085 monitors the individual series cell voltages through the bq29311. The bq2085 configures the bq29311 to present the selected cell to the VCELL pin of the bq29311 which should be connected to VIN of the bq2085. The internal ADC of the bq2085 then measures the voltage and scales it appropriately. The bq2085 then reports the Voltage( ) and the individual cell voltages in VCELL1, VCELL2, VCELL3, and VCELL4 located in 0x3c–0x3f. Current The bq2085 uses the SR1 and SR2 inputs to measure and calculate the battery charge and discharge current as represented in the data register Current( ). Temperature The TS input of the bq2085 in conjunction with an NTC thermistor measures the battery temperature as shown in the schematic. The bq2085 reports temperature in Temperature( ). The bq2085 can also be configured to use its internal temperature sensor by setting the IT bit in Misc Configuration DF 0x2a. Data flash locations DF 0xa4 through DF 0xad also have to be changed to prescribed values if the internal temperature sensor option is selected. Gas Gauge Operation Table 1. Data Flash Settings for Internal or External Temperature Sensor LABEL LOCATION Dec (Hex) INTERNAL TEMP SENSOR SETTING Dec (Hex) EXTERNAL TEMP SENSOR SETTING Dec (Hex) Misc. Configuration 42 (0x2a) Bit 7 = 1 Bit 7 = 0 TS Const1 164/5 (0xa4/5) 0 (a3) 37251 (0x9183) TS Const2 166/7 (0xa6/7) 0 (a2) 20848 (0x5170) TS Const3 168/9 (0xa8/9) –11136 (a1) 57999 (0xe28f) TS Const4 170/1 (0xaa/b) 5754 (a0) 4012 (0x0fac) TS Const5 172/3 (0xac/d) 13348 (3424) 5190 (0x1446) |
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