BQ2040_15 Datasheet, PDF (7/36 Pages) Texas Instruments – Gas Gauge IC With SMBus Interface

Not Recommended For New Designs
Inputs
Charge
Current
State-of-charge
and
Temperature
Compensation
Discharge
Current
Self-Discharge
Timer
Temperature
Compensation
Main Counters
and Capacity
Reference (FCC)
--
< + Remaining
Capacity
(RM)
Full
Charge
Capacity
(FCC)
++
Discharge
Count
Qualified _Register
Transfer _(DCR)
Temperature, Other Data
bq2040
Outputs
Chip-Controlled Two-Wire
Available Charge Serial Interface
LED Display
FG294501.eps
Figure 2. Operational Overview
ing subsequent discharges, FCC is updated with the 4. Discharge Count Register (DCR):
latest measured capacity in the Discharge Count Reg-
ister plus the battery low amount, representing a dis-
charge from full to below EDV1. A qualified dis-
charge is necessary for a capacity transfer from the
DCR to the FCC register. Once updated, the bq2040
writes the new FCC to the EEPROM. The FCC also
serves as the 100% reference threshold used by the
relative state-of-charge calculation and display.
The DCR counts up during discharge independent
of RM and can continue increasing after RM has
decremented to 0. Prior to RM = 0, both discharge
and self-discharge increment the DCR. After RM
= 0, only discharge increments the DCR. The DCR
resets to 0 when RM = FCC and stops counting at
EDV1 on discharge. The DCR does not roll over but
stops counting when it reaches FFFFh.
2. DesignCapacity (DC):
FCC is updated on the first charge after a qualified
The DC is the user-specified battery capacity and is
discharge to EDV1. The updated FCC equals the
programmed from external EEPROM. The DC also
battery low percentage times the current FCC plus
provides the 100% reference for the absolute dis-
the DCR value. A qualified discharge to EDV1 oc-
play mode.
curs if all of the following conditions exist:
3. RemainingCapacity (RM):
RM counts up during charge to a maximum value of
FCC and down during discharge and self-discharge to
0. RM is set to the battery low amount after the
EDV1 threshold has been reached. If RM is already
equal to or less than the battery low amount, RM is
not modified. If RM reaches the battery low amount
before the battery voltage falls below EDV1 on dis-
charge, RM stops counting down until the EDV1
threshold is reached. RM is set to 0 when the battery
voltage reaches EDVF. To prevent overstatement of
charge during periods of overcharge, RM stops in-
crementing when RM = FCC. RM may optionally
be written to a user-defined value when fully
charged if the battery pack is under bq2040 charge
control. On initialization, RM is set to 0.
n No valid charge initiations (charges greater than
10mAh, where VSRO > +VSRD occurred during
the period between RM = FCC and EDV1 de-
tected.
n The self-discharge count is not more than
256mAh.
n The low temperature fault bit in FLAGS2 is not
set when the EDV1 level is reached during dis-
charge.
n Battery voltage is not more than 256mV below
the EDV1 threshold when EDV1 is set.
The valid discharge flag (VDQ) in FLAGS1 indi-
cates whether the present discharge is valid for an
FCC update. FCC cannot be reduced by more than
256mAh during any single cycle.
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