Initiation and Charge Qualification
The bq2000T initiates a charge cycle when it detects
n
Application of power to VCC
n
Battery replacement
n
Exit from sleep mode
n
Capacity depletion (Li-Ion only)
Immediately following initiation, the IC enters a
charge-qualification mode. The bq2000T charge
qualification is based on battery voltage and
temperature. If voltage on pin BAT is less than the
internal threshold, VLBAT, the bq2000T enters the
charge-pending state. This condition indicates the
possiblility of a defective or shorted battery pack. In
an attempt to revive a fully depleted pack, the
bq2000T enables the MOD pin to trickle-charge at a
rate of once every 1.0s. As explained in the section
“Top-Off and Pulse-Trickle Charge,” the trickle
pulse-width is user-selectable and is set by the value
of the resistance connected to pin RC.
During this period, the LED pin blinks at a 1Hz rate,
indicating the pending status of the charger.
Similarly, the bq2000T suspends fast charge if the
battery temperature is outside the VLTF to VHTF range.
(See Table 4.) For safety reasons, however, it disables
the pulse trickle, in the case of a battery
over-temperature condition (i.e., VTS <VHTF). Fast
charge begins when the battery temperature and
voltage are valid.
Battery Chemistry
The bq2000T detects the battery chemistry by moni-
toring the battery-voltage profile during fast charge.
If the voltage on BAT input rises to the internal VMCV
reference, the IC assumes a Li-Ion battery. Otherwise
the bq2000T assumes NiCd/NiMH chemistry.
As shown in Figure 6, a resistor voltage-divider be-
tween the battery pack’s positive terminal and VSS
scales the battery voltage measured at pin BAT. In a
mixed-chemistry design, a common voltage-divider
is used as long as the maximum charge voltage of the
nickel-based pack is below that of the Li-Ion pack.
Otherwise, different scaling is required.
Once the chemistry is determined, the bq2000T
completes the fast charge with the appropriate
charge algorithm (Table 1). The user can customize
the algorithm by programming the device using an
external resistor and a capacitor connected to the RC
pin, as discussed in later sections.
NiCd and NiMH Batteries
Following qualification, the bq2000T fast-charges
NiCd or NiMH batteries using a current-limited algo-
rithm. During the fast-charge period, it monitors
charge time, temperature, and voltage for adherence
to the termination criteria. This monitoring is further
4
bq2000T
GR2000CA.eps
IMAX
IMIN
Trickle
VLBAT
VMCV
Time
Phase 1
Phase 2
Fast
Charge
Voltage
Current
Figure 3. Lithium-Ion Charge Algorithm
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