These thresholds are the following:
n
High-temperature cutoff voltage: VTCO = 0.225 ∗
VCC This voltage corresponds to the maximum
temperature (TCO) at which fast charging is
allowed. The bq2000T terminates fast charge if the
voltage on pin TS falls below VTCO.
n
High-temperature fault voltage: VHTF = 0.25 ∗ VCC
This voltage corresponds to the temperature
(HTF) at which fast charging is allowed to begin.
n
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 pin TS rises
above VLTF, the bq2000T suspends fast charge or
top-off but does not terminate charge. When the
voltage falls back below VLTF, fast charge or top-off
resumes from the point where suspended.
Trickle-charge is allowed during this condition.
Table 4 summarizes these various conditions.
Charge Status Display
The charge status is indicated by open-drain output
LED. Table 5 summarizes the display output of the
bq2000T.
10
bq2000T
Table 5. Charge Status Display
Charge Action State
LED Status
Battery absent
High
impedance
Pre-charge qualification
1Hz flash
Trickle charge (before fast charge) 1Hz flash
Fast charging
Low
Top-off or trickle (after fast
charge, NiCd, NiMH only)
High
impedance
Charge complete
High
impedance
Temperature
Condition
Action
VTS >VLTF
Cold battery—checked at all times
Suspends fast charge or top-off and timer
Allows trickle charge—LED flashes at 1Hz
rate during pre-charge qualification and fast
charge
VHTF <VTS <VLTF
Optimal operating range
Allows charging
VTS <VHTF
Hot battery—checked during charge
qualification and top-off and
trickle-charge
Suspends fast-charge initiation, does not al-
low trickle charge—LED flashes at 1Hz rate
during pre-charge qualification
Table 4. Temperature-Monitoring Conditions
2000TCS.eps
BAT-
Power Supply ground
bq2000 ground
SNS
RSNS
Rf
Cf
1
2
VSS
bq2000T
Figure 9. Current-Sensing Circuit
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