Datasheet

bq2000
SLUS138D –JANUARY 2008–REVISED DECEMBER 2009 www.ti.com
TEMPERATURE MONITORING
The bq2000 measures the temperature by the voltage at the TS pin. This voltage is typically generated by a
negative-temperature-coefficient thermistor. The bq2000 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 bq2000 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 bq2000
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 will always be 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
V
TS
> V
LTF
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
V
HTF
< V
TS
< V
LTF
Optimal charging range Allows all stages of charging
During charge qualification, stops charging
During fast charge, no effect
Hot battery – checked at all times,
V
TS
< V
HTF
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
V
TS
< V
TCO
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 (V
MCV
) 2 V
Minimum pre-charge qualification voltage (V
LBAT
) 950 mV
High-temperature cutoff voltage (V
TCO
) 0.225 × V
CC
High-temperature fault voltage (V
HTF
) 0.25 × V
CC
Low-temperature fault voltage (V
LTF
) 0.5 × V
CC
bq2000 fast-charge maximum time out (MTO) R
MTO
× C
MTO
× 35,988
Fast-charge charging current (I
MAX
) 0.05/R
SNS
Hold-off period MTO/32
Top-off charging current (optional) I
MAX
/16
Top-off period (optional) MTO
Trickle-charge frequency 1Hz
Trickle-charge pulse-width See Figure 8
(1) See the DC Thresholds Specification for details.
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