BQ2084-V133 Datasheet, PDF (7/64 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE FOR USE WITH THE bq29312

bq2084-V133
www.ti.com
TERMINAL
NAME
NO.
TSSOP
SR1
28
SR2
27
TS
2
VDDA
31
VDDD
8
VIN
1
VSSA
3, 29, 30
VSSD
11, 19, 38
XCK1/VSSA
34
XCK2/ROSC
33
Terminal Functions (continued)
SLUS640A – JUNE 2005 – REVISED JUNE 2005
I/O
DESCRIPTION
I Connections for a small-value sense resistor to monitor the battery charge- and discharge-current flow
I
I Thermistor input to monitor temperature
I Positive supply for analog circuitry
I Positive supply for digital circuitry and I/O pins
I Single-cell voltage input from the bq29312
I Negative supply for analog circuitry
I Negative supply for digital circuitry
I 32.768-kHz crystal oscillator input pin or connected to VSSA if the internal oscillator is used
O 32.768-kHz crystal oscillator output pin or connected to a 100-kΩ, 50 ppm or better resistor if the
internal oscillator is used
FUNCTIONAL DESCRIPTION
OSCILLATOR FUNCTION
The bq2084-V133 can use an internal or an external oscillator. At powerup, the bq2084-V133 automatically
attempts to start the internal oscillator. If a 100-kΩ resistor is not connected to ROSC (pin 33), then it attempts to
start the oscillator using an external 32.768-kHz crystal. Install either the 100-kΩ ROSC resistor or the 12 pF
32.768-kHz crystal, not both.
The performance of the internal oscillator depends on the tolerance of the 100-kΩ resistor connected between
RSOC (pin 33) and VSSA (pin 34). It is recommended that this resistor be as close to the bq2084-V133 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
PCB layout around these pins and components can degrade oscillator performance if not carefully implemented.
The average oscillator temperature-drift error during a learning charge or a discharge cycle introduces an equal
capacity-prediction error in the learned full-charge capacity value (FCC).
SYSTEM PRESENT OPERATION
When the bq2084-V133 detects that the battery is inserted into the system via a low state on the PRES input, the
bq2084-V133 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-V133 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.
GENERAL OPERATION
The bq2084-V133 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-V133 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-V133 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-V133 interfaces with the bq29312 to perform battery protection, cell balancing, and voltage
translation functions. The bq2084-V133 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-V133
uses temperature to monitor the battery pack and to compensate the self-discharge estimate.
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