BQ27505 Datasheet, PDF (28/42 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27505
Not Recommended for New Designs
SLUS884 – FEBRUARY 2009
www.ti.com
5.3.4 Power Path Control With the BAT_GD Pin
The bq27505 must operate in conjunction with other electronics in a system appliance, such as chargers
or other ICs and application circuits that draw appreciable power. After a battery is inserted into the
system, there should be no charging current or a discharging current higher than C/20, so that an accurate
OCV can be read. The OCV is used for helping determine which battery profile to use, as it constitutes
part of the battery impedance measurement
When a battery is inserted into a system, the Impedance Track™ algorithm requires that no charging of
the battery takes place and that any discharge is limited to less than C/20—these conditions are sufficient
for the fuel gauge to take an accurate OCV reading. To disable these functions, the BAT_GD pin is merely
negated from the default setting. Once an OCV reading has be made, the BAT_GD pin is asserted,
thereby enabling battery charging and regular discharge of the battery. The Operation Configuration
[BATG_POL] bit can be used to set the polarity of the battery good signal, should the default configuration
need to be changed.
POR
Exit From HIBERNATE
Battery Removed
Exit From HIBERNATE
Communication Activity
AND Comm address is for bq27505
bq27505 clears Control Status
[HIBERNATE ] = 0
Recommend Host also set Control
Status [HIBERNATE] = 0
BAT INSERT CHECK
Check for battery insertion
from HALT state.
No gauging
Flags [BAT _DET] = 0
Entry to NORMAL
Flags [BAT _DET] = 1
Exit From NORMAL
Flags [BAT _DET] = 0
NORMAL
Fuel gauging and data
updated every 1s
Exit From SLEEP
Flags [BAT_DET] = 0
HIBERNATE
Disable all bq27505
subcircuits except GPIO.
Negate BAT_GD
Wakeup From HIBERNATE
Communication Activity
AND
Comm address is NOT for bq27505
Entry to SLEEP+
Operation Configuration[SLEEP] = 1
AND
Control Status[SNOOZE] = 1
AND
| AverageCurrent( ) | ≤ Sleep Current
Entry to SLEEP
Operation Configuration[SLEEP] = 1
AND
| AverageCurrent( ) | ≤ Sleep Current
AND
Control Status[SNOOZE] = 0
Exit From WAIT_HIBERNATE
Cell relaxed
AND
| AverageCurrent() | < Hibernate
Current
OR
Cell relaxed
AND
VCELL < Hibernate Voltage
WAIT_HIBERNATE
Fuel gauging and data
updated every 20 seconds
BAT_GD unchanged
System Shutdown
Entry to SLEEP+
Control Status[SNOOZE] = 0
Exit From WAIT _HIBERNATE
Host must set Control Status
[HIBERNATE ] = 0
AND
VCELL > Hibernate Voltage
Exit From SLEEP
| AverageCurrent( ) | > Sleep Current
OR
Exit From SLEEP+ ^{Current is Detected above IWAKE}
Any communication to the gauge
OR
| AverageCurrent( ) | > Sleep Current
OR
Current is Detected above IWAKE
SLEEP+
Fuel gauging and data
updated every 20 seconds
Both LFO and HFO are ON
Entry to SLEEP+
Control Status[SNOOZE] = 1
SLEEP
Fuel gauging and data
updated every 20 seconds
(LFO ON and HFO OFF)
Exit From SLEEP
(Host has set Control Status
[HIBERNATE] = 1
OR
V_CELL < Hibernate Voltage
System Sleep
Figure 5-1. Power Mode Diagram
Figure 5-1 details how the BAT_GD pin functions in the context of battery insertion and removal, as well
as NORMAL vs. SLEEP modes.
28
FUNCTIONAL DESCRIPTION
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