BQ2085-V1P3 Datasheet, PDF (7/57 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

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SMBUS TIMING DIAGRAMS
SCLK
TLOW
TR
bq2085-V1P3
SLUS598 − FEBRUARY 2004
TF
THD:STA
SDATA
P
THD:STA
THD:DAT
THIGH
TSU:STA
TSU:DAT
TSU:STO
TBUF
S
S
P
Start
TLOW:SEXT
SCLKACK(1)
SCLKACK(1)
TLOW:MEXT
TLOW:MEXT
Stop
TLOW:MEXT
SCLK
SDATA
(1) _{SCLKACK is the acknowledge-related clock pulse generated by the master.}
Figure 2. SMBus Timing Diagram
FUNCTIONAL DESCRIPTION
Internal Oscillator Function
The internal oscillator performance is additionally dependent on the tolerance of the 113-kΩ resistor connected
between RSOC (pin 33) and VSSA (pin 34). It is recommended that this resistor be as close to the
bq2085−V1P3 as possible and that it have a specification of ±0.1% tolerance and ±50 ppm temperature drift
or better. The layout of the PCBA is also an additional contributing factor to 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).
General Operation
The bq2085−V1P3 determines battery capacity by monitoring the amount of charge input or removed from a
rechargeable battery. In addition to measuring charge and discharge, the bq2085−V1P3 measures battery
voltage, temperature, and current, estimates battery self-discharge, and monitors the battery for low-voltage
thresholds. The bq2085−V1P3 measures charge and discharge activity by monitoring the voltage across a
small-value series sense resistor between the battery’s 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 bq2085−V1P3 interfaces with the bq29311 to perform battery protection, cell balancing, and voltage
translation functions.
The bq2085−V1P3 can accept any NTC thermistor (default is Semitec 103AT) for temperature measurement
or can be configured to use its internal temperature sensor. The bq2085−V1P3 uses temperature to monitor
the battery pack and to compensate the self-discharge estimate.
Measurements
The bq2085−V1P3 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.
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