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BQ2000SN-B5TR Datasheet(PDF) 7 Page - Texas Instruments |
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BQ2000SN-B5TR Datasheet(HTML) 7 Page - Texas Instruments |
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7 / 18 page  nickel-based pack is below that of the Li-Ion pack. Oth- erwise, different scaling is required. Minimum Current (Li-Ion Only) The bq2000 monitors the charging current during the voltage-regulation phase of Li-Ion batteries. Fast charge is terminated when the current is tapered off to 14% of the maximum charging current. Initial Hold-Off Period The values of the external resistor and capacitor connected to pin RC set the initial hold-off period. During this period, the bq2000 avoids early termination due to an initial rise in the battery voltage by disabling the peak voltage-detection feature. This period is fixed at the programmed value of the maximum charge time divided by 32. hold-off period = maximum time - out 32 Top-Off and Pulse-Trickle Charge An optional top-off charge is available for NiCd or NiMH batteries. Top-off may be desirable on batteries that have a tendency to terminate charge before reaching full capacity. To enable this option, the capacitance value of CMTO connected to pin RC (Figure 4) should be greater than 0.13 µF, and the value of the resistor connected to this pin should be less than 15k Ω. To disable top-off, the capacitance value should be less than 0.07 µF. The toler- ance of the capacitor needs to be taken into account in component selection. Once enabled, the top-off is performed over a period equal to the maximum charge time at a rate of 116 that of fast charge. Following top-off, the bq2000 trickle-charges the battery by enabling the MOD to charge at a rate of once every 1.0 second. The trickle pulse-width is user-selectable and is set by the value of the resistor RMTO, connected to pin RC. Figure 7 shows the relationship between the trickle pulse-width and the value of RMTO. The typical tolerance of the pulsewidth below 150k Ω is ±10%. During top-off and trickle-charge, the bq2000 monitors battery voltage and temperature. These charging func- tions are suspended if the battery voltage rises above the maximum cell voltage (VMCV) or if the temperature exceeds the high-temperature fault threshold (VHTF). Charge Current Control The bq2000 controls the charge current through the MOD output pin. The current-control circuit supports a switching-current regulator with frequencies up to 500kHz. The bq2000 monitors charge current at the SNS input by the voltage drop across a sense-resistor, RSNS, in series with the battery pack. See Figure 9 for a typical current-sensing circuit. RSNS is sized to provide the desired fast-charge current (IMAX): IMAX = 0.05 RSNS If the voltage at the SNS pin is greater than VSNSLO or less than VSNSHI, the bq2000 switches the MOD output high to pass charge current to the battery. When the 7 bq2000 1 2468 10 50 100 150 200 250 2 3 4 20 40 60 RMTO—k Ω 80 100 120 140 160 180 200 2000PNvB3.eps Shows Tolerance Figure 7. Relationship Between Trickle Pulse-Width and Value of RMTO |
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Similar Description - BQ2000SN-B5TR |
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