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SP6682EU Datasheet(PDF) 7 Page - Sipex Corporation |
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SP6682EU Datasheet(HTML) 7 Page - Sipex Corporation |
7 / 12 page 7 Date: 7/1 9/06 Rev D SP6682 High Efficiency Charge Pump Regulator for White LEDs © 2006 Sipex Corporation Anode 5 8 SP6682 Cathode VOUT R6 1 R5 2.2uF VFB 2-wire W-LED module GND Figure 13. Driving 2-wire white LED module as voltage source VIN VIN C2 GND 4 VMODE R1 SP6682 8 R2 3 Figure 14. Programming the Vmode Resistors The output voltage is set by the ratio of the two resistors and the feedback control volt- age as shown by: VOUT = ( 1 + R5 ) • VFB R6 PROGRAMMING THE OPERATING MODE SP6682canautomaticallychangefromX1.5 mode to X2 mode for highest efficiency. To use this feature, divider resistors should be chosen according to the specific applica- tion, as shown in Figure 14. The guideline for divider resistor selections is as follows: For high input voltage, the SP6682 will work in X1.5 mode. When the input voltage drops to the VTH threshold voltage, it will switch to X2 mode automati- cally. The VTH threshold voltage for mode change can be calculated by: VTH = (VF + 0.306 + M • ILED • ROUT)/1.5 Where VF and M are the forward voltage and number of the white LEDs, ROUT is the output resistance of the SP6682. The equation for the voltage divider R1 and R2 with VMODE = 1.25V is: VTH = 1.25V • (1+R1/R2) which can be expressed as R1: R1 = (VTH / 1.25 -1) • R2 For the typical SP6682 application, Using VF=3.6V, M=4, ILED=15mA, ROUT=16�, the VTH will be 3.24V. Select R2=100k�, then R1=158k�. CAPACITOR SELECTION Ceramic capacitors are recommended for their inherently low ESR, which will help produce low peak to peak output ripple, and reduce high frequency spikes. The fly capacitor controls the strength of the charge pump. Selection of the fly capacitor is a trade-off between the output voltage ripple and the output current capability. Decreasing the fly capacitor will reduce the output voltage ripple because less charge will be delivered to the output capacitor. However,smallerflycapacitorsleadtolarger output resistance, thus decreasing the out- T o use the SP6682 as a voltage source for fixed voltage applications, a voltage divider is needed to program the ouput voltage, as shown in Figure 13. APPLICATION INFORMATION: Continued |
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