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BQ2056VPN Datasheet(PDF) 3 Page - Texas Instruments |
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BQ2056VPN Datasheet(HTML) 3 Page - Texas Instruments |
3 / 12 page Functional Description The bq2056 supports a precision current- and voltage- limited charging system for Li-Ion batteries. The no-load voltage regulation references (VREG) for the bq2056 and bq2056T are maintained at 4.1V and 8.2V, respectively. The bq2056V provides variable regulation to accommo- date a wide range of charge voltages and may be used to meet tighter tolerance requirements through external trimming. The functional block diagram for the bq2056 is on the first page of this data sheet, and Figure 1 illus- trates a typical application. Charge Algorithm The bq2056 completes the charge cycle in two phases. A constant current phase replenishes approximately 70% of battery capacity, while an accurate voltage regulation phase completes the charge. Figure 2 shows a typical charge algorithm for bq2056, including charge qualification, current regulation, and voltage regulation phases. Charge Qualification During charge qualification the bq2056 detects a low battery and reports this status on pin TRKL. Detection is accomplished by comparing pin BAT voltage to the in- ternal threshold VMIN. While pin BAT voltage is less than VMIN and pin INH is low, the open-drain output TRKL is driven low and the voltage/current regulator is disabled (CC=high-Z). In the bq2056V, low-voltage de- tection occurs when the voltage on pin BAT is less than or equal to VMIND. As shown in Figure 1, TRKL enables an external trickle-charge circuit to bring the battery voltage up to VMIN or VMIND. Current Regulation The bq2056 provides current regulation while the pack voltage is below the voltage limit. Charge-current feed- back, applied through pin SNS, maintains regulation around a threshold of VSNS. The following formula calcu- lates the value of the sense-resistor connected in series with the negative terminal of the battery pack (Figure 3): RSNS= 0.1/ IMAX where IMAX is the maximum charging current. IMAX should not exceed 1A. An external PNP or power P-FET may be used as the se- ries pass element with control provided through output pin CC. 3 bq2056sc.eps INH TRKL bq2056 VS COMP VCC CC BAT SNS 1 2 3 4 8 7 6 5 BAT+ BAT- R6 0.3 C1 10 F 10V C2 0.1 F R2 1K R1 1K DC+ DC- R5 2K R5 2.7K D1 1N5817 Q1 2N3906 2TX788B Q2 5 VDC R3 4.7K Figure 1. Low-Dropout Single-Cell Li-Ion Charger bq2056/T/V |
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