BQ2000 Datasheet, PDF (4/18 Pages) Texas Instruments – Programmable Multi-Chemistry Fast-Charge Management IC

bq2000
Initiation and Charge Qualification
The bq2000 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 bq2000 charge qualifica-
tion is based on battery voltage and temperature. If
voltage on pin BAT is less than the internal threshold,
VLBAT, the bq2000 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 bq2000 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 bq2000 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 bq2000 detects the battery chemistry by monitoring
the battery-voltage profile during the initial stage of the
fast charge. If the voltage on BAT input rises to the in-
ternal VMCV reference, the IC assumes a Li-Ion battery.
Otherwise the bq2000 assumes NiCd/NiMH chemistry.
As shown in Figure 6, a resistor voltage-divider between
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. Oth-
erwise, different scaling is required.
Once the chemistry is determined, the bq2000 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 bq2000 fast-charges NiCd or
NiMH batteries using a current-limited algorithm. Dur-
ing the fast-charge period, it monitors charge time, tem-
perature, and voltage for adherence to the termination
criteria. This monitoring is further explained in later
sections. Following fast charge, the battery is topped off,
if top-off is selected. The charging cycle ends with a
trickle maintenance-charge that continues as long as
the voltage on pin BAT remains below VMCV.
I_MAX
Trickle
I_MIN
Voltage
Fast Charge
Phase 1
Phase 2
Current
V_MCV
V_LBAT
Time
GR2000CA.eps
Figure 3. Lithium-Ion Charge Algorithm
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