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LP3945ILDX Datasheet(PDF) 8 Page - National Semiconductor (TI) |
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LP3945ILDX Datasheet(HTML) 8 Page - National Semiconductor (TI) |
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8 / 15 page  Application Notes LP3945 CHARGER OPERATION The LP3945 is a complete battery charger with I 2C interface. Charge cycle is initiated with wall adaptor insertion. If the wall adaptor voltage appearing on the CHG-IN pin meets under-voltage (V UVLO-TSHD), over-voltage (VOVLO-TSHD), and the Adaptor OK signal is detected, then pre-conditioning process begins (see Figure 1). In pre-qualification cycle, a safe current level, less than 65 mA, is pumped into the battery while the voltage across the battery terminals is measured. Once this voltage exceeds 3.0V, the controller will initiate constant current fast charge cycle. During this cycle, the 5.6 hr safety timer is started and charge current is increased to I CHG. The default value for ICHG is set during manufacturing to 500 mA but it is user programmable from 500 mA to 950 mA in 50 mA step. The programmed current is determined by battery type and manufacturers’ recom- mendation. If safety timer times out during constant current cycle, charg- ing will be terminated if StopModeEN pin is pulled high. If it is pulled low, device will proceed to operate in maintenance mode and have to be interrupted externally. This is not a recommended mode of operation. Disabling the 5.6hr timer can potentially expose the battery to prolong charge cycle and damage the battery. If StopModeEN feature is used, user must protect the battery from exposure to prolong charge cycle. As the battery is charged during constant current mode, the voltage across pack terminal increases until it reaches 4.1V (or 4.2V). As soon as pack terminal exceeds 4.1V (or 4.2V), controller starts operating in constant voltage mode by ap- plying regulated V BATT voltage across the battery terminal. During this cycle, charge current, I CHG, continues to de- crease with time and when it drops below 0.1C (by default), the EOC signal is activated indicating successful completion of the charge cycle. The "C" term in 0.1C is the programmed I CHG. For example, 0.1C of 700mA is 70mA, and 0.2C of 700mA is 140mA. EOC current can be programmed to 0.1C, 0.15C, or 0.2C. The default value is 0.1C. After completing the full charge cycle, controller will start maintenance cycle where battery pack voltage is monitored continuously. If during the maintenance cycle, pack voltage drops below 3.9V, charge cycle will be initiated providing that the wall adaptor is plugged in and is alive. Ni-MH charge mode (LP3945 only), which is a constant voltage mode charging, can be selected by setting the “mode” bit to HIGH via the I 2C interface. The LP3945 with I 2C programming allows maximum flexibil- ity in selecting charge current, battery regulation voltage (4.1V or 4.2V), EOC current and battery type (Li Ion or Ni-MH). The LP3945 operates in default mode during power up. See the “I 2C Interface” section for more detail. LP3946 CHARGER OPERATION The LP3946 is a simpler version of the LP3945. It does not have any I 2C interface, thus the device operates on default setting. The values in BOLD in Table 1 are the default settings. Default settings can be set at the factory to custom- er’s specifications. For other options, please contact a Na- tional Semiconductor sales office. The LP3946 charges only Li Ion type battery. TABLE 1. LP3946 Performance Options Battery Voltage Regulation (V) End of Charge Current Threshold (mA) Charge Current (mA) 4.1 0.1C 500 4.2 0.15C 550 0.20C 600 650 700 750 800 850 900 950 20066510 FIGURE 1. Charger Power Up and Power Down Waveform www.national.com 8 |
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