bq2000T

SLUS149D – MAY 1999 – REVISED JANUARY 2010

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TEMPERATURE MONITORING

The bq2000T measures the temperature by the voltage at the TS pin. This voltage is typically generated by a

negative-temperature-coefficient thermistor. The bq2000T compares this voltage against its internal threshold

voltages to determine if charging is safe. These thresholds are the following:

•

High-temperature cutoff voltage: VTCO = 0.225 × VCC . This voltage corresponds to the maximum temperature

(TCO) at which any charging is allowed. The bq2000T terminates charging if the voltage on the TS pin falls

below VTCO.

•

High-temperature fault voltage: VHTF = 0.25 × VCC . This voltage corresponds to a maximum allowed pack

temperature (HTF) in all states except for fast charge. During fast charge, HTF faults are disabled to allow for

a normal increase in pack temperature.

•

Low-temperature fault voltage: VLTF = 0.5 × VCC . This voltage corresponds to the minimum temperature

(LTF) at which fast charging or top-off is allowed. If the voltage on the TS pin rises above VLTF, the bq2000T

suspends either fast charge or top-off and begins a trickle charge. When the voltage falls back below VLTF,

fast charge or top-off resumes from the point where suspended. If VTS > VLTF, the charger is always in trickle

charge.

Table 3 summarizes these various conditions.

Table 3. Temperature-Monitoring Conditions and Actions

TEMPERATURE

CONDITION

ACTION

During charge qualification, no effect

During fast charge, suspends fast charge and moves into charge

qualification, pauses timer, and flashes LED

VTS > VLTF

Cold battery – checked at all times

During top-off, suspends top-off and moves into trickle maintenance

charge and pauses timer

During trickle maintenance charge, no effect

VHTF < VTS < VLTF

Optimal charging range

Allows all stages of charging

During charge qualification, stops charging

During fast charge, no effect

Hot battery – checked at all times,

VTS < VHTF

except during fast charge

During top-off, stops charging

During trickle maintenance charge, stops charging

During charge qualification, stops charging

During fast charge, terminates fast charge and stops charging, turns off

Battery exceeding maximum

LED

VTS < VTCO

allowable temperature – checked at

all times

During top-off, terminates top-off and stops charging

During trickle maintenance charge, stops charging

Table 4. Summary of NiCd or NiMH Charging Characteristics

PARAMETER

VALUE(1)

Maximum cell voltage (VMCV)

2 V

Minimum pre-charge qualification voltage (VLBAT)

950 mV

High-temperature cutoff voltage (VTCO)

0.225 × VCC

High-temperature fault voltage (VHTF)

0.25 × VCC

Low-temperature fault voltage (VLTF)

0.5 × VCC

bq2000T fast-charge maximum time out (MTO)

RMTO × CMTO × 35,988

Fast-charge charging current (IMAX)

0.05/RSNS

Hold-off period

MTO/32

Top-off charging current (optional)

IMAX/16

Top-off period (optional)

MTO

Trickle-charge frequency

1 Hz

Trickle-charge pulse-width

See Figure 7

(1)

See the DC Thresholds Specification for details.

14

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