bq2085-V1P3
SLUS598 − FEBRUARY 2004
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Charge and Discharge Counting
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 as shown in the schematic. The integrating ADC measures bipolar
signals from −0.3 to 1.0 V. The bq2085−V1P3 detects charge activity when V
SR
= V
(SR1)
–V
(SR2)
is positive and
discharge activity when V
SR
= V
(SR1)
–V
(SR2)
is negative. The bq2085−V1P3 continuously integrates the signal
over time, using an internal counter. The fundamental rate of the counter is 2.6 nVh. The bq2085−V1P3 updates
Remaining Capacity() with the charge or discharge accumulated in this internal counter once every second.
Offset Calibration
The bq2085−V1P3 provides an autocalibration feature to cancel the voltage offset error across SR
1
and SR
2
for maximum charge measurement accuracy. The bq2085−V1P3 performs autocalibration when the SMBus
lines stay low for a minimum of 20 s. The bq2085−V1P3 is capable of automatic offset calibration down to 1
µV.
Digital Filter
The bq2085−V1P3 does not measure charge or discharge counts below the digital filter threshold. The digital
filter threshold is programmed in the
Digital Filter
DF 0x2b. Set it sufficiently high to prevent false signal detection
with no charge or discharge flowing through the sense resistor.
Voltage
While monitoring SR1 and SR2 for charge and discharge currents, the bq2085−V1P3 monitors the individual
series cell voltages through the bq29311. The bq2085−V1P3 configures the bq29311 to present the selected
cell to the VCELL pin of the bq29311. Therefore, connect the VCELL pin to VIN of the bq2085−V1P3. The
internal ADC of the bq2085−V1P3 then measures the voltage and scales it appropriately. The bq2085−V1P3
then reports the Voltage( ) and the individual cell voltages in VCELL1, VCELL2, VCELL3, and VCELL4 located
in 0x3c−0x3f.
Current
The bq2085−V1P3 uses the SR1 and SR2 inputs to measure and calculate the battery charge and discharge
current as represented in the data register Current().
Temperature
The TS input of the bq2085−V1P3 in conjunction with an NTC thermistor measures the battery temperature
as shown in the schematic. The bq2085−V1P3 reports temperature in Temperature( ).
The bq2085−V1P3 can also be configured to use its internal temperature sensor by setting the IT bit in
Misc
Configuration
DF 0x2a. Data flash locations DF 0xa4 through DF 0xad also have to be changed to prescribed
values if the internal temperature sensor option is selected.
Table 1. Data Flash Settings for Internal or External Temperature Sensor
LABEL
Misc. Configuration
TS Const1 A3
TS Const2 A2
TS Const3 A1
TS Const4 A0
Min Temp AD
Max Temp
LOCATION
Dec (Hex)
42 (0x2a)
164/5 (0xa4/5)
166/7 (0xa6/7)
168/9 (0xa8/9)
170/1 (0xaa/b)
172/3 (0xac/d)
174/5 (0xae/f)
INTERNAL TEMP SENSOR SETTING
Dec (Hex)
Bit 7 = 1
0 (0x0000)
0 (0x0000)
−11136 (0xd480)
5754 (0x1666)
0 (0x0000)
5734 (0x1666)
EXTERNAL TEMP SENSOR SETTING
(Semitec 103AT)
Dec (Hex)
Bit 7 = 0
−28285 (0x9183)
20848 (0x5170)
−7537 (0xe28f)
4012 (0x0fac)
0 (0x0000)
4012 (0x0fac)
If AD < Min Temp AD then Temp = Max Temp
Else
Temp = ([A3
×
AD
×
2^ − 16 + A2]
×
AD
×
2^ − 16 + A1)
×
AD 2^ −16 + A0
8
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