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LTC4055 Datasheet(PDF) 11 Page - Linear Technology |
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LTC4055 Datasheet(HTML) 11 Page - Linear Technology |
11 / 24 page 11 LTC4055 4055p OPERATIO The LTC4055 is a complete PowerPath controller for battery-powered USB applications. The LTC4055 is de- signed to provide device power and Li-ion battery charg- ing from the USB VBUS while maintaining the current limits as specified in the USB specification. This is accomplished by reducing battery charge current as output/load current is increased. In this scenario, the available bus current is maximized in an effort to minimize battery charge time. An ideal diode function provides power from the battery when output/load current exceeds the input current limit set for the part or when input power is removed. The advantage to powering the load through the ideal diode (rather than connecting the load directly to the battery) is that when the bus is connected and the battery is fully charged, the battery remains fully charged until bus power is removed. Once bus power is removed the output drops until the ideal diode is forward biased. The forward biased ideal diode will then provide the output power to the load from the battery. Another advantage to powering the load from the bus when the bus is available is in cases where the load is a switching regulator. The input power to a switching regu- lator can be thought of as constant. A higher voltage across a constant power load will require less current. Less load current in USB applications means more avail- able charge current. More charge current translates to shorter charge times. The LTC4055 also has the ability to accommodate power from a wall adapter. Wall adapter power can be connected to the output (load side) of the LTC4055 through an external device such as a power Schottky or FET, as shown in Figure 1. The LTC4055 has the unique ability to use the output, which is powered by the wall adapter, as an alternate path to charge the battery while providing power to the load. A wall adapter comparator on the LTC4055 can be configured to detect the presence of the wall adapter and shut off the connection to the USB to prevent reverse conduction out to the bus. – + 1 + INPUT CHARGER CONTROL ENABLE IN2 5 WALL 1V 4 IN1 VBUS AC 3 OUT 2 BAT 4055 F01 UVLO CURRENT LIMIT CONTROL ENABLE OUTPUT CHARGER CONTROL ENABLE IDEAL Li-Ion LOAD Figure 1. Simplified Block Diagram—PowerPath |
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