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BQ24400DRG4 Datasheet(PDF) 6 Page - Texas Instruments |
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BQ24400DRG4 Datasheet(HTML) 6 Page - Texas Instruments |
6 / 27 page MTO hold-off period = 32 bq24400 SLUS498A – SEPTEMBER 2001 – REVISED FEBRUARY 2010 www.ti.com Initiation and Charge Qualification The bq24400 initiates a charge cycle when it detects • Application of power to VCC • Battery replacement • Exit from sleep mode Immediately following initiation, the IC enters a charge-qualification mode. The bq24400 charge qualification is based on battery voltage and temperature. If the voltage on the BAT pin is less than the internal threshold, VLBAT, the bq24400 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 bq24400 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 VSS. 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 VLBAT, the IC enters fast charge, if the battery temperature is within the VLTF to VHTF range. The bq24400 will stay in the battery conditioning state indefinitely and will not progress to fast charge until the voltage on the BAT pin is above VLBAT and the temperature is within the VLTF and VHTF range. No timer is implemented during battery conditioning. Fast Charge (Current Regulation) Following charge qualification (which includes trickle charge, if required), the bq24400 begins fast charge fast 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. While in the fast charge state, the LED pin is pulled low (the LED is on). 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 VMCV. Table 1 summarizes the charging process. Table 1. Charge Algorithm BATTERY CHEMISTRY CHARGE ALGORITHM 1. Charge qualification 2. Trickle charge, if required 3. Fast charge (constant current) NiCd or NiMH Batteries (VBAT < VMCV always) 4. Fast charge termination (peak voltage, maximum charge time = 1 MTO) 5. Top-off (optional) 6. Trickle charge FAST CHARGE TERMINATION Initial Hold-Off Period The bq24400 incorporates a user programmable hold-off period to avoid premature fast charge termination that can occur with brand new nickel cells at the very beginning of fast charge. The values of the external resistor and capacitor connected to the RC pin set the initial hold-off period. During this period, the bq24400 avoids early termination due to an initial peak in the battery voltage by disabling the peak voltage-detection (PVD) feature. This period is fixed at the programmed value of the maximum charge time (MTO) divided by 32. (1) 6 Submit Documentation Feedback Copyright © 2001–2010, Texas Instruments Incorporated Product Folder Link(s): bq24400 |
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