BQ27546-G1 Datasheet, PDF (17/38 Pages) Texas Instruments – nullSingle-Cell Li-Ion Battery Fuel Gauge

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bq27546-G1
SLUSC53A – MAY 2015 – REVISED DECEMBER 2015
Device Functional Modes (continued)
During SLEEP mode, the bq27546-G1 periodically takes data measurements and updates its data set. However,
a majority of its time is spent in an idle condition.
The bq27546-G1 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 when the I_WAKE comparator
is enabled.
9.4.1.3 FULLSLEEP Mode
FULLSLEEP mode is entered automatically when the bq27546-G1 is in SLEEP mode and the timer counts down
to 0 (Full Sleep Wait Time > 0). FULLSLEEP mode is entered immediately after entry to SLEEP if Full Sleep
Wait Time is set to 0 and the host sets the [FULLSLEEP] bit in the CONTROL_STATUS register using the
SET_FULLSLEEP subcommand.
The gauge exits the FULLSLEEP mode when there is any communication activity. The [FULLSLEEP] bit can
remain set (Full Sleep Wait Time > 0) or be cleared (Full Sleep Wait Time ≤ 0) after exit of FULLSLEEP mode.
Therefore, EVSW communication activity might cause the gauge to exit FULLSLEEP mode and display the
[FULLSLEEP] bit as clear. The execution of SET_FULLSLEEP to set [FULLSLEEP] bit is required when Full
Sleep Wait Time ≤ 0 in order to re-enter FULLSLEEP mode. FULLSLEEP mode can be verified by measuring
the current consumption of the gauge. In this mode, the high frequency oscillator is turned off. The power
consumption is further reduced in this mode compared to SLEEP mode.
While in FULLSLEEP mode, the fuel gauge can suspend serial communications as much as 4 ms by holding the
comm line(s) low. This delay is necessary to correctly process host communication, since the fuel gauge
processor is mostly halted in SLEEP mode.
The bq27546-G1 exits FULLSLEEP 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 when the I_WAKE comparator
is enabled.
9.4.1.4 HIBERNATE Mode
HIBERNATE mode should be used for long-term pack storage or when the host system needs to enter a low-
power state and minimal gauge power consumption is required. This mode is ideal when the host is set to its
own HIBERNATE, SHUTDOWN, or OFF mode. The gauge waits to enter HIBERNATE mode until it has taken a
valid OCV measurement (cell relaxed) and the value of the average cell current has fallen below Hibernate
Current. When the conditions are met, the fuel gauge can enter HIBERNATE due to either low cell voltage or by
having the [HIBERNATE] bit of the CONTROL_STATUS register set. The gauge remains in HIBERNATE mode
until any communication activity appears on the communication lines and the address is for the bq27546-G1
device. In addition, the SE pin SHUTDOWN mode function is supported only when the fuel gauge enters
HIBERNATE due to low cell voltage.
When the gauge wakes up from HIBERNATE mode, the [HIBERNATE] bit of the CONTROL_STATUS register is
cleared. The host is required to set the bit in order to allow the gauge to re-enter HIBERNATE mode if desired.
Because the fuel gauge is dormant in HIBERNATE mode, the battery should not be charged or discharged in this
mode, because any changes in battery charge status will not be measured. If necessary, the host equipment can
draw a small current (generally infrequent and less than 1 mA) for purposes of low-level monitoring and updating;
however, the corresponding charge drawn from the battery will not be logged by the gauge. Once the gauge
exits to NORMAL mode, the IT algorithm will take approximately 3 s to re-establish the correct battery capacity
and measurements, regardless of the total charge drawn in HIBERNATE mode. During this period of re-
establishment, the gauge reports values previously calculated prior to entering HIBERNATE mode. The host can
identify exit from HIBERNATE mode by checking if Voltage() < Hibernate Voltage or [HIBERNATE] bit is cleared
by the gauge.
If a charger is attached, the host should immediately take the fuel gauge out of HIBERNATE mode before
beginning to charge the battery. Charging the battery in HIBERNATE mode will result in a notable gauging error
that will take several hours to correct. It is also recommended to minimize discharge current during exit from
HIBERNATE.
Copyright © 2015, Texas Instruments Incorporated
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