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BQ2084DBTR-V140 Datasheet(PDF) 7 Page - Texas Instruments |
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BQ2084DBTR-V140 Datasheet(HTML) 7 Page - Texas Instruments |
7 / 64 page www.ti.com FUNCTIONAL DESCRIPTION OSCILLATOR FUNCTION SYSTEM PRESENT OPERATION GENERAL OPERATION bq2084-V140 SLUS664B – JULY 2005 – REVISED AUGUST 2006 Terminal Functions (continued) TERMINAL I/O DESCRIPTION NO. NO. NAME TSSOP QFN SMBus data open-drain bidirectional pin used to transfer address and data to SMBD 16 1 I/O and from the bq2084-V140 SR1 28 13 I Connections for a small-value sense resistor to monitor the battery charge- and discharge-current flow SR2 27 12 I TS 2 24 I Thermistor voltage input connection to monitor temperature VDDA 31 16 I Positive supply for analog circuitry VDDD 8 30 I Positive supply for digital circuitry and I/O pins VIN 1 25 I Single-cell voltage input from the bq29312 VSSA 3, 29, 30 14, 15 I Negative supply for analog circuitry VSSD 11, 19, 38 4, 22, 23, 33 I Negative supply for digital circuitry 32.768-kHz crystal oscillator input pin or connected to VSSA if the internal XCK1/VSSA 34 19 I oscillator is used 32.768-kHz crystal oscillator output pin or connected to a 100-k Ω, 50 ppm or XCK2/ROSC 33 18 O better resistor if the internal oscillator is used The oscillator of the bq2084-V140 can be set up for an internal or external operation. As the bq2084-V140 powers up it automatically attempts to start the internal oscillator, but if a 100-k Ω resistor is not connected to ROSC (pin 33), then it attempts to start the oscillator using an external 32.768-kHz crystal. Either the 100-k Ω ROSC resistor OR the 12 pF 32.768-kHz crystal should be mounted, NOT both. The performance of the internal oscillator depends on the tolerance of the 100-k Ω resistor connected between RSOC (pin 33) and VSSA (pin 34). It is recommended that this resistor be as close to the bq2084-V140 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-V140 detects that the battery is inserted into the system via a low state on the PRES input, the bq2084-V140 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-V140 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-V140 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-V140 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-V140 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. 7 Submit Documentation Feedback |
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