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SC600AIMSTRT Datasheet(PDF) 7 Page - Semtech Corporation |
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SC600AIMSTRT Datasheet(HTML) 7 Page - Semtech Corporation |
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7 / 19 page  7 © 2006 Semtech Corp. www.semtech.com POWER MANAGEMENT SC600 Applications Information Regulated Fractional Charge Pump Operation A fractional charge pump is a voltage converter which implements switched capacitor techniques to produce an output voltage that is one of several multiples of the input voltage. Regulated fractional charge pumps (also called charge pump regulators) use a linear regulator with vari- ous charge pump configurations to deliver a regulated out- put over a wide input voltage range. Regulated fractional charge pumps have improved efficiency over ordinary lin- ear regulator and charge pump circuit combinations. The improved efficiency is achieved by implementing multiple charge pump configurations on one integrated circuit. The correct charge pump configuration is automatically selected to meet the regulation requirements at the best possible efficiency. The SC600 has three charge pump configurations (modes), which multiply the input voltage by 1x, 1.5x and 2x. The charge pump configurations are implemented with two switched or 'bucket' capacitors plus the input and out- put capacitor. The bucket capacitors are configured for 1x mode at start-up to source current to the output capacitor and bring the output up quickly. The charge pump will begin switching in 1.5x mode. During normal operation, starting with a fully charged Li-Ion cell, the battery voltage will begin at about 4.1V. As the battery discharges and the voltage decays, the SC600 will eventually transition to 2x mode when the battery voltage is approximately 3.50V. Hysteresis is provided to prevent mode toggling. The out- put is prevented from exceeding 6.0V. This feature allows the use of 6.3V ceramic capacitors. mAhXLiFETM Advantage The plot on page 1 shows the efficiency of the SC600A. An example of a 5.0V regulated charge pump doubler is plotted to demonstrate how effective the SC600’s 1.5x mode is at improving efficiency when the input voltage is above 3.5V. Most of the Li-Ion battery life is above 3.5V where the SC600 achieves more than 20% higher effi- ciency compared to the 5.0V regulated charge pump dou- bler with only a 2x mode. Following the efficiency curve from left to right as the battery discharges, the SC600A 5.0V remains in 1.5x mode until 3.5V and then transitions to 2x mode. Component Versions There are four versions of the SC600. The component selection table on page 4 highlights the differences be- tween the component types. The three basic differences between the component versions are in the output volt- age, maximum output current capability, and the mode transition point. The mode transition point is the value of input voltage at which the component will transition between 1.5x and 2x modes. 5.0V, 4.5V, and 4.0V versions are available. The SC600A (5.0V) is most efficient for applications that use up to 60mA. The SC600B (4.5V) and SC600C (4.5V) have different maximum output currents and mode transition points. The lower mode transition point of the SC600C allows it to remain in 1.5x mode longer for greater power savings. The SC600B has higher output capability, up to 120mA, and S600C is rated for 60mA. The SC600D (4.0V) is for applications using up to 120mA. Start-Up Conditions Typical start-up time is less than 50μs. Caution: The SC600 must be enabled while 650kHz or 262kHz is selected to pre- vent over-voltage during start-up. LED Bias and Backlighting Applications When using the SC600 for LED bias, note that the SC600C and SC600D require the same input power per unit of output current even though the SC600C is more efficient. Also, the SC600A will have the same input power as the SC600B though the SC600A is more efficient. The following plots of Input Power vs. Input Voltage high- light the differences in application of the four component versions. To achieve the lowest possible input power, it is desirable for the charge pump to remain in 1.5x mode until the input voltage is as low as possible. The transi- tion points from 1.5x to 2x are identified in the plot where the input power steps upward as the input voltage moves lower. |
Similar Part No. - SC600AIMSTRT |
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Similar Description - SC600AIMSTRT |
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