BQ2054 Datasheet, PDF (3/16 Pages) Texas Instruments – Lithium Ion Fast-Charge IC

bq2054
Charge Algorithm
The bq2054 uses a two-phase fast charge algorithm. In
phase 1, the bq2054 regulates constant current (ISNS =
IMAX) until VCELL (= VBAT - VSNS) rises to VREG. The
bq2054 then transitions to phase 2 and regulates con-
stant voltage (VCELL = VREG) until the charging current
falls below the programmed IMIN threshold. The charg-
ing current must remain below IMIN for 120 ± 40ms bef-
ore a valid fast charge termination is detected. Fast
charge then terminates, and the bq2054 enters the
Charge Complete state. See Figures 1 and 2.
Charge Qualification
The bq2054 starts a charge cycle when power is applied
while a battery is present or when a battery is inserted.
Figure 2 shows the state diagram for pre-charge qualifi-
cation and temperature monitoring. The bq2054 first
checks that the battery temperature is within the al-
lowed, user-configurable range. If the temperature is out
of range, the bq2054 enters the Charge Pending state
and waits until the battery temperature is within the al-
lowed range. Charge Pending is enunciated by LED3
flashing.
Thermal monitoring continues throughout the charge
cycle, and the bq2054 enters the Charge Pending state
when the temperature out of range. (There is one excep-
tion; if the bq2054 is in the Fault state—see below—the
out-of-range temperature is not recognized until the
bq2054 leaves the Fault state.) All timers are sus-
pended (but not reset) while the bq2054 is in Charge
Pending. When the temperature comes back into range,
the bq2054 returns to the point in the charge cycle
where the out-of-range temperature was detected.
When the temperature is valid, the bq2054 then regu-
lates current to ICOND (=IMAX/5). After an initial holdoff
period tHO (which prevents the chip from reacting to
transient voltage spikes that may occur when charge
current is first applied), the chip begins monitoring
VCELL. If VCELL does not rise to at least VMIN before the
expiration of time-out limit tMTO (e.g. the cell has failed
short), the bq2054 enters the Fault state. If VMIN is
achieved before expiration of the time limit, the chip be-
gins fast charging.
Once in the Fault state, the bq2054 waits until VCC is
cycled or a new battery insertion is detected. It then
starts a new charge cycle and begins the qualification
process again.
IMAX
ICOND
IMIN
Voltage
Fast Charge
Phase 1
Phase 2
Current
VREG
VMIN
Time
Figure 1. bq2054 Charge Algorithm
GR205401.eps
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