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LX2205 Datasheet(PDF) 10 Page - Microsemi Corporation |
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LX2205 Datasheet(HTML) 10 Page - Microsemi Corporation |
10 / 14 page LX2205 PRODUCTION DATA SHEET Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 Copyright © 2007 Rev. 1.0a, 2007-03-02 1A Li-Ion Battery Charger with Power Source Management TM ® TH EORY OF O PERAT ION Battery Current w ith 100m A USB Current Lim it -80 -60 -40 -20 0 20 40 60 80 100 120 0 40 80 120 160 System Load Current (m A) USB Limit Battery REDUCED USB CHARGE TIME The isolated battery topology reduces charge time from the USB port when the appliance is turned on while also charging. Because the system power rail can be a higher voltage than the battery voltage, the system will require less power from the USB source which leaves more power available to charge the battery quickly. For example, if the system draws 1W, and the USB input is 5V, the system draws 1W/5V = 200mA from the USB source; this leaves 300mA to charge the battery. In a topology where the load connects directly to the battery (as is done with conventional non-isolated linear chargers), if the average battery voltage is 3.7V, the system will draw 1W/3.7V = 270mA from the USB source, this leaves only 230mA to charge the battery. In this case the LX2205 will charge the battery 30% faster. USB SUSPEND When the SUSP pin is pulled high, less than 25μA is pulled from the USB port. The rest of the LX2205, however, continues to function normally. If an adapter is applied, the effect of SUSP is negligible. If the system is running off both USB and the battery and SUSP is logic high, the system load will be transferred 100% to the battery. SHDN When SHDN is logic high, the LX2205 is placed in a total shutdown mode; no current will flow between SYS, USB and BAT. Quiescent current is 25μA during shutdown. CHG and DONE are high impedance (off) in SHDN mode. UCL The UCL pin is used to select the current limit level for the USB input. When the UCL pin is a logic high the maximum current level as determined by the CUS resistor is selected; when the UCL pin is a logic low, the current limit is set to 20% of the maximum level. POWER OR-ING (SYS TO BAT AND BAT TO SYS) When the power is removed from both MDC and USB, the battery current flows from BAT to SYS and thus provides power to the load without the need for any external switches or monitoring circuits. There is a circuit equivalent of an ideal diode (patent-pending bi-directional MOSFET) in the LX2205 between the BAT pin and SYS pin. This ideal diode appears as a low impedance to high forward current and presents a high impedance to low discharge currents or potentially reverse charge currents. For small forward currents, the ideal diode regulates a small forward voltage. This small voltage allows the power sense circuitry to determine whether an input power source is present even if the current through the ideal diode is less than 1mA. This feature makes it virtually impossible to charge the battery (unregulated) in reverse through the ideal diode and also enables the battery to assist a current limited input power source without chattering even if only a few mA of battery current are required. |
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