BQ2000T_15 Datasheet, PDF (14/29 Pages) Texas Instruments – Programmable Multi-Chemistry Fast-Charge Management IC

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: V_TCO = 0.225 × V_CC . 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 V_TCO.
• High-temperature fault voltage: V_HTF = 0.25 × V_CC . 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: V_LTF = 0.5 × V_CC . 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 V_LTF, the bq2000T
suspends either fast charge or top-off and begins a trickle charge. When the voltage falls back below V_LTF,
fast charge or top-off resumes from the point where suspended. If V_TS > V_LTF, the charger is always in trickle
charge.
Table 3 summarizes these various conditions.
TEMPERATURE
V_TS > V_LTF
V_HTF < V_TS < V_LTF
V_TS < V_HTF
V_TS < V_TCO
Table 3. Temperature-Monitoring Conditions and Actions
CONDITION
Cold battery – checked at all times
Optimal charging range
Hot battery – checked at all times,
except during fast charge
Battery exceeding maximum
allowable temperature – checked at
all times
ACTION
During charge qualification, no effect
During fast charge, suspends fast charge and moves into charge
qualification, pauses timer, and flashes LED
During top-off, suspends top-off and moves into trickle maintenance
charge and pauses timer
During trickle maintenance charge, no effect
Allows all stages of charging
During charge qualification, stops charging
During fast charge, no effect
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
LED
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 (V_MCV)
Minimum pre-charge qualification voltage (V_LBAT)
High-temperature cutoff voltage (V_TCO)
High-temperature fault voltage (V_HTF)
Low-temperature fault voltage (V_LTF)
bq2000T fast-charge maximum time out (MTO)
Fast-charge charging current (I_MAX)
Hold-off period
2V
950 mV
0.225 × V_CC
0.25 × V_CC
0.5 × V_CC
R_MTO × C_MTO × 35,988
0.05/R_SNS
MTO/32
Top-off charging current (optional)
Top-off period (optional)
I_MAX/16
MTO
Trickle-charge frequency
1 Hz
Trickle-charge pulse-width
See Figure 7
(1) See the DC Thresholds Specification for details.
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