BQ27505-J4 Datasheet, PDF (22/38 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27505-J4
SLVSA40 – DECEMBER 2009
www.ti.com
Class
Gas Gauging
Gas Gauging
Subclass
ID
82
82
Subclass
State
State
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Calibration
104
Data
Data
Data
Data
Data
Data
Data
Data
Calibration
107
Current
Security
112
Security
112
Security
112
Security
112
Security
112
(2) Not IEEE floating point.
Codes
Codes
Codes
Codes
Codes
Data Flash Summary (continued)
Offset
Name
18 Avg P Last Run
20 Delta Voltage
Data Type
I2
I2
Min
Value
–32,768
–32,768
0
CC Gain
4
CC Delta
8
CC Offset
10 ADC Offset
12 Board Offset
13 Int Temp Offset
14 Ext Temp Offset
15 Pack V Offset
F4 ⁽²⁾
F4 ⁽²⁾
I2
I2
I1
I1
I1
I1
0.1
4.7
–2.4
–500
–128
–128
–128
–128
1
Deadband
U1
0
0
Unseal Key 0
2
Unseal Key 1
4
Full-Access Key 0
6
Full-Access Key 1
24 FactRestore Key
H2
0x0000
H2
0x0000
H2
0x0000
H2
0x0000
H4
0x00000000
5 FUNCTIONAL DESCRIPTION
Max
Value
32,767
32,767
47
188
2.4
500
127
127
127
127
255
0xffff
0xffff
0xffff
0xffff
0xffffffff
Default
Value
–1200
2
10⁽¹⁾
10⁽¹⁾
–0.123 ⁽¹⁾
0
0
0
0
0
5
0x3672
0x0414
0xffff
0xffff
0x0FAC0DEF
Units
mAh
mV
mohm
mohm
mV
mV
mV
0.1°C
0.1°C
mV
mA
–
–
–
–
–
5.1 FUEL GAUGING
The bq27505-J4 measures the cell voltage, temperature, and current to determine battery SOC. The
bq27505-J4 monitors charge and discharge activity by sensing the voltage across a small-value resistor
(5mΩ to 20mΩ typ.) between the SRP and SRN pins and in series with the cell. By integrating charge
passing through the battery, the battery’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
bq27505-J4 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 bq27505-J4 has two flags accessed by the Flags( ) function that warns when the battery’s SOC has
fallen to critical levels. When RemainingCapacity( ) falls below the first capacity threshold, specified in
SOC1 Set Threshold, the [SOC1] (State of Charge Initial) flag is set. The flag is cleared once
RemainingCapacity( ) rises above SOC1 Set Threshold. The bq27505-J4’s BAT_LOW pin automatically
reflects the status of the [SOC1] flag. All units are in mAh.
When Voltage( ) falls below the system shut down threshold voltage, SysDown Set Volt Threshold, the
[SYSDOWN] flag is set, serving as a final warning to shut down the system. The SOC_INT also signals.
When Voltage( ) rises above SysDown Clear Voltage and the [SYSDOWM] flag has already been set,
the [SYSDOWN] flag is cleared. The SOC_INT also signals such change. All units are in mV.
22
FUNCTIONAL DESCRIPTION
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