BQ27350 Datasheet, PDF (19/33 Pages) Texas Instruments – Single Cell Li-Ion Battery Manager With Impedance Track Fuel Gauge Technology

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Class
Gas Gauging
Gas Gauging
Gas Gauging
Gas Gauging
Gas Gauging
Ra Table
Ra Table
Ra Table
Ra Table
Calibration
Calibration
Calibration
Calibration
Calibration
Calibration
Calibration
Calibration
Subclass
ID
82
82
82
82
82
88
88
89
89
104
104
104
104
104
104
104
107
bq27350
Single Cell Li-Ion Battery Manager
With Impedance Track Fuel Gauge Technology
SLUS754 – MARCH 2007
Table 4-9. Data Flash Summary (continued)
Subclass
State
State
State
State
State
Offset
0
2
6
9
11
Name
Qmax Cell 0
Qmax Pack
Update Status
Avg I Last Run
Avg P Last Run
Data
Type
I2
I2
H1
I2
I2
Min
Value
0
0
0x00
–32768
–32768
Max
Value
32767
32767
0x06
32767
32767
Default
Value
1500
1500
0x0
–2000
–3022
Units
mAh
mAh
mA
mW
R_a0
R_a0
0
2 – 30
Cell0 R_a flag
Cell0 R_a [0 –14]
H2
0x0000 0x0000
0xff55
I2
183
183
160
2^-10Ω
R_a0x
R_a0x
0
2 – 30
xCell0 R_a flag
xCell0 R_a [0 –14]
H2
0xffff
0xffff
I2
183
183
0xffff
160
2^-10Ω
Data
Data
Data
Data
Data
Data
Data
0
CC Gain
4
CC Delta
8
Ref Voltage
10
CC Offset
12
Board Offset
14
Int Temp Offset
15
Ext1 Temp Offset
F4
0.1
4
0.9419
F4
0.1
4
0.9419
I2
0
32767
1225
I2
–32768 32767
–1667
I2
–32767 32767
0
I1
–128
127
0
I1
–128
127
0
Current
1
Deadband
U1
0
255
3
mA
5 FUNCTIONAL DESCRIPTION
5.1 FUEL GAUGING
The bq27350 measures the cell voltage, temperature, and current to determine battery SOC. The
bq27350 monitors charge and discharge activity by sensing the voltage across a small-value resistor
(5mΩ to 20 mΩ typ.) between the SRP and SRN pins and in-series with the cell. By integrating charge
passing through the battery, the cell’s SOC is adjusted during battery charge or discharge.
The total battery capacity is found by comparing states of charge before and after applying the load with
the amount of charge passed. When an application load is applied, the impedance of the cell is measured
by comparing the OCV obtained from a predefined function for present SOC with the measured voltage
under load. Measurements of OCV and charge integration determine chemical state of charge and
Chemical Capacity (Qmax). The initial Qmax value is taken from a cell manufacturers' data sheet
multiplied by the number of parallel cells. It is also used for the value in Design Capacity. The bq27350
acquires and updates the battery-impedance profile during normal battery usage. It uses this profile, along
with SOC and the Qmax value, to determine FullChargeCapacity( ) and StateOfCharge( ) specifically for
the present load and temperature. FullChargeCapacity( ) is reported as capacity available from a fully
charged battery under the present load and temperature until Voltage( ) reaches the Terminate Voltage.
NominalAvailableCapacity( ) and FullAvailableCapacity( ) are the uncompensated (no or light load)
versions of RemainingCapacity( ) and FullChargeCapacity( ) respectively.
The bq27350 has two flags accessed by the Flags( ) function that warns when the cell’s SOC has fallen to
critical levels. When RemainingCapacity( ) falls below the first capacity threshold, specified in RCA Set,
the [RCA] (“Remaining Capacity Alert”) flag is set. The flag is cleared once RemainingCapacity( ) rises
above RCA Set. All units are in mAh.
When StateOfCharge( ) falls below the second capacity threshold, TDA Set %, the [TDA] (“Terminate
Discharge Alert”) flag is set, serving as a final discharge warning. If TDA Set % = -1, the flag is inoperative
during discharge.
Similarly, when StateOfCharge( ) rises above TDA Clear % and the [TDA] flag has already been set, the
[TDA] flag will be cleared, provided TDA Set % ≠– 1. All units are in percentages.
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FUNCTIONAL DESCRIPTION
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