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SP7685EB Datasheet(PDF) 4 Page - Exar Corporation |
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SP7685EB Datasheet(HTML) 4 Page - Exar Corporation |
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4 / 13 page  4 Date: 6/20/06 Rev T SP7685, 1.2A Buck/BoostCharge Pump LED Driver © 2006 Sipex Corporation FUNCTIONAL DIAGRAM The SP7685 is a charge pump regulator designed for converting a Li-Ion battery voltage of 2.7V to 4.2V to drive a white LED used in digital still camera Flash and Torch applications. The SP7685 has two modes of operation which are pin-selectable for either Flash or Torch. Flash mode is usually used with a pulse of about 200 to 300 milliseconds to generate a high intensity Flash. Torch can be used continuously at a lower output current than Flash and is often used for several seconds in a digital still camera “movie” mode. The SP7685 also has two modes of opera- tion to control the output current: the 1X mode and 2X mode. Operation begins after the enable pin EN receives a logic high, the bandgap reference wakes up after 200μs, and then SP7685 goes through a soft-start mode designed to reduce inrush current. The SP7685 starts in the 1X mode, which THEORY OF OPERATION acts like a linear regulator to control the output current by continuously monitoring the feedback pin FB. In 1X mode, if the SP7685 auto detects a dropout condition, which is when the FB pin is below the regulation point for more than 32 cycles of the internal clock, the SP7685 automati- cally switches to the 2X mode. The SP7685 remains in the 2X mode until one of four things happens: 1) the enable pin EN has been toggled, 2) the Flash pin has changed from high to low, 3) V IN is cycled or, 4) a thermal fault occurs. The 2X mode is the charge pump mode where the output can be pumped as high as two times the input voltage, provided the output does not exceed the maximum volt- age for the SP7685, which is internally limited to about 5.5V. In the 2X mode, as in the 1X mode, the output current is regulated by the voltage at the FB pin. RSET BLOCK 6 RSET RSET RSET REF= { 5 RSET } x14μA + - 1.26V + - BG REF RSET REF RESISTOR TAPS 50mV 4 FLASH FLASH=1, S=1, RSET REF FLASH=0, S=0, 50mV 1 0 s MUX 2x1 FB REF 7 FB SGND 8 FB COM P + - FB COMP CLR COUNTER 32 COUNT ONE SHOT SET DOMINANT S R 0 MODE SWITCH 0 =1X 1=2X 1 5 EN VIN 135C ON 145C OFF THERMAL FAULT OVER TEMP COMP CLK CLK 2.4MHZ CHARGE PUMP SWITCHES PGND C1 C2 VOUT CLK |
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