BQ2054SN datasheet(8/19 Pages) TI1

8 / 19 page

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:

TCO (Temperature Cutoff): Higher limit of the tem-

perature range in which charging is allowed. VTCO =

0.4*VCC

HTF (High-Temperature Fault): Threshold to which

temperature must drop after temperature cutoff is

exceeded before charging can begin again.

VHTF =

0.44 * VCC

LTF (Low-Temperature Fault):

Lower limit of the

temperature range in which charging is allowed.

VLTF =0.6*VCC

VCC

VLTF = 0.6VCC

VHTF = 0.44VCC

VTCO = 0.4VCC

Hotter

VSS

TCO

HTF

LTF

Colder

Figure 6. Voltage Equivalent

of Temperature

SNS

bq2054

VCC

BAT -

VSS

RSNS

RT2

RT1

VSS

VCC

˚t

NTC

Thermistor

Figure 5. Configuring

Temperature Sensing

bq2054

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