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SP6683EU Datasheet(PDF) 6 Page - Sipex Corporation |
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SP6683EU Datasheet(HTML) 6 Page - Sipex Corporation |
6 / 10 page 6 Date: 07/07/04 SP6683 White LEDs Driver for Parallel Configuration © Copyright 2004 Sipex Corporation 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, smaller fly capaci- tor leads to larger output resistance, thus de- creasing the output current capability and the circuit efficiency. Place all the capacitors as close to the SP6683 as possible for layout. Increasing the value of the input and otput capicitors could further reduce the input and output ripple. Refer to table 1 for some suggested low ESR capicitors. PROGRAMMING THE OPERATING MODE SP6683 can automatically change from X1 mode to X1.5 mode for highest efficiency. To use this feature, divider resistors should be chosen ac- cording to the specific application, as shown in figure 13. V IN V IN C2 GND 4 V MODE R1 SP6683 8 R2 3 Figure 13. Programming the Vmode Resistors The guideline for divider resistor selections is as follows. For high input voltage, the SP6683 will work in X1 mode. When the input voltage drops to Vth threshold voltage, it will switch to X1.5 mode automatically. The Vth threshold voltage for mode change can be calculated by: VTH = (VF + 0.306 + m • ILED • ROUT) Where VF and m are the forward voltage and number of the white LEDs, Rout is the output resistance of the SP6683. The equation for the voltage divider R1 and R2 with VMODE = 1.25V is: VTH = 1.25V • (1+R1/R2) APPLICATION INFORMATION For the typical SP6683 application, using VF = 3.6V, m = 8, ILED = 15mA, ROUT = 6Ω, VTH will be 4.63V, Select R2 = 100kΩ, then R1 = 270kΩ Which can be expressed as R1: R1 = VTH/1.25 - 1) • R2 MANUFACTURERS/ PART NUMBER CAPACITANCE/ CAPACITOR/ ESR TELEPHONE# VOLTAGE SIZE/TYPE AT 100kHz TDK/847-803-6100 C2012X5R1A225K 2.2µF/10V 0805/X5R 0.030Ω TDK/847-803-6100 C2012X5R0J475K 4.7µF/6.3V 0805/X5R 0.020Ω MURATA/770-436-1300 GRM188R60J225KE01D 2.2µF/6.3V 0603/X5R 0.030Ω MURATA/770-436-1300 GRM219R60J475KE01D 4.7µF/6.3V 0805/X5R 0.020Ω Table: 1 SUGGESTED LOW ESR CAPACITORS |
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