BQ27520-G2 Datasheet, PDF (34/47 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated LDO

bq27520-G2
SLUSAB7A – MARCH 2011 – REVISED AUGUST 2011
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The bq27520-G2 exits SLEEP if any entry condition is broken, specifically when (1) AverageCurrent( )
rises above Sleep Current, or (2) a current in excess of I_WAKE through R_SENSE is detected.
In the event that a battery is removed from the system while a charger is present (and powering the
gauge), Impedance Track™ updates are not necessary. Hence, the fuel gauge enters a state that checks
for battery insertion and does not continue executing the Impedance Track™ algorithm.
5.7.4 SLEEP+ MODE
Compared to the SLEEP mode, SLEEP+ mode has the high frequency oscillator in operation. The
communication delay could be eliminated. The SLEEP+ is entered automatically if the feature is enabled
(CONTROL STATUS [SNOOZE] = 1) and AverageCurrent( ) is below the programmable level Sleep
Current.
During SLEEP+ mode, the bq27520-G2 periodically takes data measurements and updates its data set.
However, a majority of its time is spent in an idle condition.
The bq27520-G2 exits SLEEP+ if any entry condition is broken, specifically when (1) any communication
activity with the gauge, or (2) AverageCurrent( ) rises above Sleep Current, or (3) a current in excess of
I_WAKE through R_SENSE is detected.
5.7.5 HIBERNATE MODE
HIBERNATE mode should be used when the system equipment needs to enter a low-power state, and
minimal gauge power consumption is required. This mode is ideal when a system equipment is set to its
own HIBERNATE, SHUTDOWN, or OFF modes.
Before the fuel gauge can enter HIBERNATE mode, the system must set the [HIBERNATE] bit of the
CONTROL_STATUS register. The gauge waits to enter HIBERNATE mode until it has taken a valid OCV
measurement and the magnitude of the average cell current has fallen below Hibernate Current. The
gauge can also enter HIBERNATE mode if the cell voltage falls below Hibernate Voltage and a valid
OCV measurement has been taken. The gauge will remain in HIBERNATE mode until the system issues a
direct I²C command to the gauge or a POR occurs. I²C Communication that is not directed to the gauge
will not wake the gauge.
It is important that BAT_GD be deserted status (no battery charging/discharging). This prevents a charger
application from inadvertently charging the battery before an OCV reading can be taken. It is the system’s
responsibility to wake the bq27520-G2 after it has gone into HIBERNATE mode. After waking, the gauge
can proceed with the initialization of the battery information (OCV, profile selection, etc.)
5.8 POWER CONTROL
5.8.1 WAKE-UP COMPARATOR
The wake up comparator is used to indicate a change in cell current while the bq27520-G2 is in SLEEP
mode. Operation Configuration uses bits [RSNS1–RSNS0] to set the sense resistor selection.
Operation Configuration also uses the [IWAKE] bit to select one of two possible voltage threshold
ranges for the given sense resistor selection. An internal interrupt is generated when the threshold is
breached in either the charge or discharge direction. Setting both [RSNS1] and [RSNS0] to 0 disables this
feature.
Table 5-7. I_WAKE Threshold Settings⁽¹⁾
RSNS1
0
0
RSNS0
0
0
IWAKE
0
1
Vth(SRP–SRN)
Disabled
Disabled
(1) The actual resistance value vs the setting of the sense resistor is not important, just the actual voltage
threshold when calculating the configuration. The voltage thresholds are typical values under room
temperature.
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FUNCTIONAL DESCRIPTION
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