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MIC79050-4.2BS Datasheet(PDF) 9 Page - Micrel Semiconductor |
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MIC79050-4.2BS Datasheet(HTML) 9 Page - Micrel Semiconductor |
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9 / 20 page  June 2000 9 MIC79050 MIC79050 Micrel Applications Information Simple Lithium-Ion Battery Charger. Figure 1A shows a simple, complete lithium-ion battery charger. The charging circuit comprises of a cheap wall adapter, with a load-line characteristic. This characteristic is always present with cheap adapters due to the internal impedance of the transformer windings. The load-line of the unregulated output should be < 4.4V to 4.6V at somewhere between 0.5C to 1C of the battery under charge. This 4.4 to 4.6V value is an approximate number based on the head- room needed above 4.2V for the MIC79050 to operate correctly e.g. For a 500mAhr battery, the output of the semi- regulated supply should be between 225mA to 500mA ( 0.5C to 1C ). If it is below 225mA no damage will occur but the battery will take longer to charge. Figure 1B shows a typical wall adapter characteristic with an output current of 350mA at 4.5V. This natural impedance of the wall adapter will limit the max current into the battery, so no external circuitry is needed to accomplish this. If extra impedance is needed to achieve the desired loadline, extra resistance can easily be added in series with the MIC79050 IN pin. LM4041 CIM3-1.2 IN BAT FB GND EN MIC79050-4.2BM VREF = 1.225V Impedence AC Load-line Wall Adapter 10k 4.7 µF 1k End of Charge R2 R1 MIC6270 VV R1 R2 EOC REF =+ 1 VS Figure 1A. Load-Line Charger With End-Of-Charge Termination Circuit. 0 2 4 6 8 0 0.2 0.4 0.6 0.8 SOURCE CURRENT (A) Load-Line Source Characteristics Figure 1B. Load-Line Characteristics of AC Wall Adapter |
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