BQ27425-G1 Datasheet, PDF (22/32 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated Sense Resistor

bq27425-G1
SLUSAI6 – NOVEMBER 2011
www.ti.com
DETECTING CHARGE TERMINATION
The bq27425 detects charge termination when (1) during 2 consecutive periods of Current Taper Window
(default = 40 seconds), the AverageCurrent( ) is < Taper Current (default = 100 mA), (2) during the same
periods, the accumulated change in capacity > 0.25mAh/ / Current Taper Window (default = 40 seconds), and
(3) Voltage( ) > (Charging Voltage – 100mV) where Charging Voltage = 4200mV by default. When this occurs,
the [CHG] bit of Flags( ) is cleared. Also, if the [RMFCC] bit of Operation Configuration is set, and
RemainingCapacity( ) is set equal to FullChargeCapacity( ).
Charge Inhibit
The bq27425 can indicate when battery temperature has fallen below or risen above predefined thresholds
Charge Inhibit Temp Low (default = 0˚C) or Charge Inhibit Temp High (default = 45˚C), respectively. In this
mode, the [CHG_INH] of Flags( ) is made high to indicate this condition, and is returned to its low state, once
battery temperature returns to the range [Charge Temp Low, Charge Temp High] (default = [5˚C,40˚C]).
OPERATING MODES
The bq27425 has different operating modes: POR, INITIALIZATION, NORMAL, CONFIG UPDATE, SLEEP, and
HIBERNATE. Following Power On Reset (POR), the fuel gauge begins INITIALIZATION. In NORMAL mode, the
bq27425 is fully powered and can execute any allowable task. Configuration data in RAM and NVM can be
updated by the host using the CONFIG UPDATE mode. In SLEEP mode the fuel gauge turns off the high
frequency oscillator clock to enter a reduced-power state, periodically taking measurements and performing
calculations. In HIBERNATE mode, the fuel gauge is in a very low power state, but can be woken up by
communication or certain I/O activity.
Exit From HIBERNATE
V _CELL < POR threshold
Power On Reset [POR]
Copy configuration ROM
defaults to RAM data.
Set Flags[ITPOR] = 1.
Flags
[BAT _ DET ] = 0
INITIALIZATION
Initialize algorithm and data.
Check for battery ins.ertion.
(No gauging in this mode.)
I _CC = Normal
via RESET
subcommand
(from any mode)
Exit from CONFIG UPDATE
Flags [CFGUPMODE] = 0
AND
Flags [ITPOR] = 0
(via SOFT_RESET
subcommand)
Entry to NORMAL
Flags [ BAT _ DET ] = 1
Exit From NORMAL
Flags [BAT _ DET ] = 0
CONFIG UPDATE
Host can change RAM and
NVM based data blocks.
(No gauging in this mode.)
Entry to CONFIG UPDATE
Flags [CFGUPMODE] = 1
(via SET_CFGUPDATE
subcommand)
Exit From HIBERNATE
Communication Activity
OR
bq27425 clears Control Status
[HIBERNATE ] = 0
Recommend Host also set Control
Status [HIBERNATE ] = 0
NORMAL
Fuel gauging and data
updated every 1s
ICC = Normal
Exit From SLEEP /FULLSLEEP
Pack Configuration [SLEEP ] = 0
OR
| AverageCurrent ( ) | > Sleep Current
OR
Current is Detected above I WAKE
HIBERNATE
Disable all subcircuits
except GPIO .
I CC = Hibernate
Wakeup From HIBERNATE
Communication to gauge
AND
Comm address is NOT for bq27425
Entry to SLEEP
Pack Configuration [SLEEP ] = 1
AND
| AverageCurrent ( ) | = Sleep Current
Exit From WAIT _HIBERNATE
Host must set Control Status
[HIBERNATE ] = 0
AND
VCELL > Hibernate Voltage
SLEEP
Fuel gauging and data
updated every 20 seconds
I _CC = Sleep
Exit From WAIT _ HIBERNATE
Cell relaxed
AND
| AverageCurrent () | < Hibernate
Current
OR
Cell relaxed
AND
V CELL < Hibernate Voltage
WAIT _HIBERNATE
Fuel gauging and data
updated every 20 seconds
I CC = Sleep /FullSleep
Exit From SLEEP
( Host has set Control Status
[HIBERNATE ] = 1
OR
VCELL < Hibernate Voltage
System Sleep
System Shutdown
Figure 2. Power Mode Diagram
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