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SP6686 Datasheet(PDF) 10 Page - Sipex Corporation |
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SP6686 Datasheet(HTML) 10 Page - Sipex Corporation |
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10 / 13 page  10 Date: 03/10/06 SP6686 400mA, Buck/Boost Charge Pump LED Driver © Copyright 2006 Sipex Corporation For an example of 150mA Torch mode and 400mA Flash mode, the values R SENSE = 0.33Ω, V FB = 135mV (Flash Mode), and RSET = 106KΩ are calculated. The power ob- tained in the Flash mode would be: P FLASH = VFB *IOUT = 133mV*400mA = 53mW. The typical 0603 surface mount resistor is rated at 1/10 Watt continuous power and 1/5 Watt pulsed power, more than enough for this application. For other applications, the P FLASH can be calculated from the resis- tor size selected. The R SENSE resistor is recommended to be size 0603 for most applications. COMPONENT SELECTION The SP6686 charge pump circuit requires 3 capacitors: 4.7µF input, 1µF output and 0.47µF fly capacitor are typically recom- mended. For the input capacitor, a larger value of 10µF will help reduce input voltage ripple for applications sensitive to ripple on the battery voltage. All the capacitors should be ceramic to obtain low ESR, which improves bypassing on the input and output and improves output voltage drive by reduc- ing output resistance. X5R or X7R Ceramic capacitors are recommended for most ap- plications. A selection of recommended ca- pacitors is included in Table 1. The input and output capacitors should be located as close to the V IN and VOUTpins as possible to obtain best bypassing, and the returns should be connected directly to the P GND pin or to the thermal pad ground located under the SP6686. The fly capacitor should be located as close to the C1 and C2 pins as possible. The sense resistor R sense is determined by the value needed in the Torch mode for the desired output current by the equation: R SENSE = VFB / IOUT where VFB = 50mV (Torch Mode) Once the R SENSE resistor has been selected for Torch mode, the V FB voltage can be selected for Flash mode using the following equation: V FB = IOUT *RSENSE (Flash Mode) where IOUT is for Flash Mode Next, the R SET resistor can be selected for Flash mode using the following equation: R SET = (1.26V/ VFB)*11.2KΩ (Flash Mode) Table 1: Recommended Capacitors Manufacturers/ Website Part Number Capacitance/ Voltage Capacitor Size/Type/Thickness ESR at 100KHz TDK/www.tdk.com C1005X5R0J474K 0.47uF/6.3V 0402/X5R/0.55mm 0.03 TDK/www.tdk.com C1005X5R0J105K 1uF/6.3V 0402/X5R/0.55mm 0.03 TDK/www.tdk.com C1608X5R0J225K 2.2uF/6.3V 0603/X5R/0.9mm 0.03 TDK/www.tdk.com C1608X5R0J475K 4.7uF/6.3V 0603/X5R/0.9mm 0.02 Murata/www.murata.com GRM155R60J474KE19D 0.47uF/6.3V 0402/X5R/0.55mm 0.03 Murata/www.murata.com GRM155R60J105KE19D 1uF/6.3V 0402/X5R/0.55mm 0.03 Murata/www.murata.com GRM188R60J225KE19D 2.2uF/6.3V 0603/X5R/0.8mm 0.03 Murata/www.murata.com GRM188R60J475KE19D 4.7uF/6.3V 0603/X5R/0.8mm 0.02 |
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