BQ2054 Datasheet, PDF (8/16 Pages) Texas Instruments – Lithium Ion Fast-Charge IC

bq2054
Battery Insertion and Removal
VCELL is interpreted by the bq2054 to detect the pres-
ence or absence of a battery. The bq2054 determines
that a battery is present when VCELL is between the
High-Voltage Cutoff (VHCO = VREG + 0.25V) and
the Low-Voltage Cutoff (VLCO = 0.8V). When VCELL is
outside this range, the bq2054 determines that no bat-
tery is present and transitions to the Fault state. Tran-
sitions into and out of the range between VLCO and VHCO
are treated as battery insertions and removals, respec-
tively. The VHCO limit also implicitly serves as an over-
voltage charge termination.
Inrush Current Control
Whenever the bq2054 is in the fault or charge-complete
state, the ICTL output is driven low. This output can be
used to disconnect the capacitor usually present in the
charger across the positive and negative battery termi-
nals, preventing the cap from supplying large inrush
currents to a newly inserted battery. Such inrush cur-
rents may trip the overcurrent protection circuitry usu-
ally present in Li-Ion battery packs.
Temperature Monitoring
The bq2054 monitors temperature by examining the
voltage presented between the TS and SNS pins by a re-
sistor network that includes a Negative Temperature
Coefficient (NTC) thermistor. Resistance variations
around that value are interpreted as being proportional
to the battery temperature (see Figure 6).
The temperature thresholds used by the bq2054 and
their corresponding TS pin voltage are:
n TCO (Temperature Cutoff): Higher limit of the tem-
perature range in which charging is allowed. VTCO =
0.4 * VCC
n HTF (High-Temperature Fault): Threshold to which
temperature must drop after temperature cutoff is
exceeded before charging can begin again. VHTF =
0.44 * VCC
n LTF (Low-Temperature Fault): Lower limit of the
temperature range in which charging is allowed.
VLTF = 0.6 * VCC
VCC
bq2054
RT1
13
VCC
12
VSS
VSS
SNS ⁷
TS ⁸
NTC
Thermistor
RT2 RT
˚t
BAT -
RSNS
VCC
VLTF = 0.6VCC
VHTF = 0.44VCC
VTCO = 0.4VCC
VSS
Colder
LTF
HTF
TCO
Hotter
Figure 5. Configuring
Temperature Sensing
Figure 6. Voltage Equivalent
of Temperature
8