BQ27500 Datasheet, PDF (20/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
www.ti.com
Class
Ra Tables
Ra Tables
Ra Tables
Ra Tables
Subclass
ID
91
92
93
94
Table 4-7. Data Flash Summary (continued)
Subclass
Pack0 Ra
Pack1 Ra
Pack0 Rax
Pack1 Rax
Offset
0-18
0-18
0-18
0-18
Name
See Note⁽²⁾
Data
Type
Min
Value
Max
Value
Default
Value
Units
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Data
Data
Data
Data
Data
Data
Data
0
CC Gain
4
CC Delta
8
CC Offset
10
Board Offset
11
Int Temp Offset
12
Ext Temp Offset
13
Pack V Offset
F4
0.1
4
0.47095
mΩ
F4
29826 1193046 280932.6
mΩ
I2
-32768 32767
–1667
mV
I1
–128
127
0
mV
I1
–128
127
0
0.1°C
I1
–128
127
0
0.1°C
I1
–128
127
0
0.1°C
Calibration
107
Current
1
Deadband
U1
0
255
3
mA
Security
112
Codes
Security
112
Codes
Security
112
Codes
Security
112
Codes
0
Usealed Key0
2
Usealed Key1
4
Full-Access Key0
6
Full-Access Key1
H2
0x0000
0xffff
–
–
H2
0x0000
0xffff
–
–
H2
0x0000
0xffff
–
–
H2
0x0000
0xffff
–
–
5 FUNCTIONAL DESCRIPTION
5.1 FUEL GAUGING
The bq27500/1 measures the cell voltage, temperature, and current to determine battery SOC. The
bq27500/1 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 values are 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 bq27500/1
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 Term Voltage.
NominalAvailableCapacity( ) and FullAvailableCapacity( ) are the uncompensated (no or light load)
versions of RemainingCapacity( ) and FullChargeCapacity( ) respectively.
The bq27500/1 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 SOC1
Set, the [SOC1] (“State of Charge Initial””) flag is set. The flag is cleared, once RemainingCapacity( ) rises
above SOC1 Set. All units are in mAh.
When RemainingCapacity( ) falls below the second capacity threshold, SOCF Set, the [SOCF] (“State of
Charge Final”) flag is set, serving as a final discharge warning. If SOCF Set = –1, the flag is inoperative
during discharge.
Similarly, when RemainingCapacity( ) rises above SOCF Clear and the [SOCF] flag has already been set,
the [SOCF] flag will be cleared, provided SOCF Set ≠ –1. All units are in mAh.
20
FUNCTIONAL DESCRIPTION
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