BQ2084-V140_14 Datasheet, PDF (7/64 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE FOR USE WITH THE bq29312

bq2084-V140
www.ti.com
NAME
SMBD
SR1
SR2
TS
VDDA
VDDD
VIN
VSSA
VSSD
XCK1/VSSA
TERMINAL
NO.
TSSOP
16
28
27
2
31
8
1
3, 29, 30
11, 19, 38
34
XCK2/ROSC
33
NO.
QFN
1
13
12
24
16
30
25
14, 15
4, 22, 23, 33
19
18
Terminal Functions (continued)
SLUS664B – JULY 2005 – REVISED AUGUST 2006
I/O
DESCRIPTION
I/O
SMBus data open-drain bidirectional pin used to transfer address and data to
and from the bq2084-V140
I
Connections for a small-value sense resistor to monitor the battery charge- and
I
discharge-current flow
I
Thermistor voltage input connection 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 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-kΩ 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-kΩ
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-kΩ 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).
SYSTEM PRESENT OPERATION
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.
GENERAL OPERATION
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.
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