BQ2000_15 Datasheet, PDF (6/29 Pages) Texas Instruments – Programmable Multi-Chemistry Fast-Charge Management IC

bq2000
SLUS138D – JANUARY 2008 – REVISED DECEMBER 2009
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Initiation and Charge Qualification
The bq2000 initiates a charge cycle when it detects
• Application of power to V_CC
• Battery replacement
• Exit from sleep mode
• Capacity depletion (Li-Ion only)
Immediately following initiation, the IC enters a charge-qualification mode. The bq2000 charge qualification is
based on battery voltage and temperature. If the voltage on the BAT pin is less than the internal threshold, V_LBAT,
the bq2000 enters the battery conditioning state. This condition indicates the possibility 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 Maintenance Charge," the trickle
pulse-width is user-selectable and is set by the value of the resistance connected between the RC pin and V_SS.
During charge qualification, the LED pin blinks at a 1Hz rate, indicating the pending status of the charger.
Once battery conditioning (trickle charge) has raised the voltage on the BAT pin above V_LBAT, the IC enters fast
charge, if the battery temperature is within the V_LTF to V_HTF range. The BQ2000 will stay in the battery
conditioning state indefinitely and will not progress to fast charge until the voltage on the BAT pin is above V_LBAT
and the temperature is within the V_LTF and V_HTF range. No timer is implemented during battery conditioning.
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 the BAT pin rises to the internal V_MCV reference, the IC assumes a Li-Ion battery.
Otherwise, the bq2000 assumes a NiCd/NiMH chemistry. While in the fast charge state, the LED pin is pulled low
(the LED is on).
As shown in Figure 3, a resistor voltage-divider between the battery pack's positive terminal and V_SS scales the
battery voltage. A low-pass filter then smooths out this voltage to present a clean signal to the BAT pin. 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.
2
V_SS
4
BAT
bq2000
BAT+
R_B1
R_B2
Figure 3. Battery Voltage Divider and Filter
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 charge qualification (which includes trickle charge, if required ), the bq2000 fast-charges NiCd or NiMH
batteries using a current-limited algorithm. During the fast-charge period, it monitors charge time, temperature,
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 the BAT pin remains below V_MCV.
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