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SP6691EK1 Datasheet(PDF) 3 Page - Sipex Corporation |
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SP6691EK1 Datasheet(HTML) 3 Page - Sipex Corporation |
3 / 15 page Jun26-07 Rev D Micro Power Boost Regulator Series White LED Driver © 2007 Sipex Corporation + - 4 Q1 Q2 R3 R4 R2 R1 X1 Shutdown Logic 250ns ONE-SHOT CLEAR X2 + - SET DRIVER GND 2 1 5 3 SW POWER TRANSISTOR DISABLE VIN SHDN FB THEORY OF OPERATION Operation can be best understood by referring to the functional diagram above and the typical application circuit in the front page. Q1 and Q2 along with R3 and R4 form a band gap refer- ence. The input to this circuit completes a feed- back path from the high voltage output through a voltage divider, and is used as the regulation control input. When the voltage at the FB pin is slightly above 1.22V, comparator X1 disables most of the internal circuitry. Current is then provided by capacitor C2, which slowly dis- charges until the voltage at the FB pin drops below the lower hysteresis point of X1, about 6mV. X1 then enables the internal circuitry, turns on chip power, and the current in the inductor begins to ramp up. When the current through the driver transistor reaches about 450mA, comparator X2 clears the latch, which turns off the driver transistor for a preset 250nS. At the instant of shutoff, inductor current is diverted to the output through diode D1. During this 250nS time limit, inductor current decreases while its energy charges C2. At the end of the 250ns time period, driver transistor is again allowed to turn on which ramps the current back up to the 450mA level. Comparator X2 clears the latch, it’s output turns off the driver transistor, and this allows delivery of L1’s stored kinetic energy to C2. This switch- ing action continues until the output capacitor voltage is charged to the point where FB is at band gap (1.22V). When this condition is reached, X1 turns off the internal circuitry and the cycle repeats. FUNCTIONAL DIAGRAM PIN DESCRIPTION PIN NUMBER PIN NAME DESCRIPTION 1 SW Switch input to the internal power switch. 2 GND Ground 3 FB Feedback 4 SHDN Shutdown. Pull high (on) to enable. Pull low (off) for shutdown. 5 VIN Input Voltage. Bypass this pin with a capacitor as close to the device as possible. |
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