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BQ2084DBTRG4 Datasheet(PDF) 8 Page - Texas Instruments |
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BQ2084DBTRG4 Datasheet(HTML) 8 Page - Texas Instruments |
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8 / 69 page  www.ti.com SYSTEM PRESENT OPERATION GENERAL OPERATION MEASUREMENTS CHARGE AND DISCHARGE COUNTING OFFSET CALIBRATION bq2084-V143 SLUS732 – SEPTEMBER 2006 FUNCTIONAL DESCRIPTION (continued) RSOC (pin 33) and VSSA (pin 34). It is recommended that this resistor be as close to the bq2084-V143 as possible and that it has a specification of ±0.1% tolerance and ±50 ppm temperature drift or better. The 12-pF crystal, if used, should also be placed as close to the XCK1 (pin 34) and XCK2 (pin 33) pins as possible. The layout of the PCB around these pins and components is also an additional contributing factor to oscillator performance degradation. The average temperature drift error of the oscillator function over a learning charge or discharge cycle introduces an equal capacity prediction error in a learned full charge capacity (FCC). When the bq2084-V143 detects that the battery is inserted into the system via a low state on the PRES input, the bq2084-V143 enters normal operating mode and sets the PRES bit in PackStatus(). The discharge FET turns on within 250 ms of pack insertion. When the pack is removed from the system and the PRES input is high, then the bq2084-V143 enters the battery removed state and turns OFF the charge and discharge FETs, and enables the 0-V/precharging FET. If NR in Misc Config is set, then the PRES input can be left floating as it is not used. The bq2084-V143 determines battery capacity by monitoring the amount of charge input or removed from a rechargeable battery. In addition to measuring charge and discharge, the bq2084-V143 measures individual cell voltages, pack voltage, temperature, and current, estimates battery self-discharge, and monitors the battery for low-voltage thresholds using features of the bq29312 AFE device. The bq2084-V143 measures charge and discharge activity by monitoring the voltage across a small-value series sense resistor between the cell stack negative terminal and the negative terminal of the battery pack. The available battery charge is determined by monitoring this voltage and correcting the measurement for environmental and operating conditions. The bq2084-V143 interfaces with the bq29312 to perform battery protection, cell balancing, and voltage translation functions. The bq2084-V143 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-V143 uses temperature to monitor the battery pack and to compensate the self-discharge estimate. The bq2084-V143 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. 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 µV. The bq2084-V143 detects charge activity when VSR = V(SR1)-V(SR2) is positive and discharge activity when VSR = V(SR1)-V(SR2) is negative. The bq2084-V143 continuously integrates the signal over time, using an internal counter. The fundamental rate of the counter is 0.65 nVh. The bq2084-V143 updates RemainingCapacity() with the charge or discharge accumulated in this internal counter once every second. The bq2084-V143 provides an auto-calibration feature to cancel the voltage offset error across SR1 and SR2 for maximum charge measurement accuracy. The bq2084-V143 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-V143 is capable of automatic offset calibration down to <1 µV. 8 Submit Documentation Feedback |
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