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SP6685ER Datasheet(PDF) 8 Page - Sipex Corporation |
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SP6685ER Datasheet(HTML) 8 Page - Sipex Corporation |
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8 / 10 page  8 Date: 12/15/04 SP6685 Charge Pump LED Driver for Camera Flash © Copyright 2004 Sipex Corporation For an example of 200mA Torch mode and 600mA Flash mode, the values R SENSE = 0.25Ω, V FBREF = 150mV (Flash Mode), and R SET = 88.7K are calculated. The power obtained in the Flash mode would be: P FLASH = VFB *IOUT = 150mV*600mA = 90mW. The typical 0603 surface mount resistor is rated 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 resistor size selected. The R SENSE resistor is recom- mended to be size 0603 for most applica- tions. COMPONENT SELECTION 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) The SP6685 charge pump circuit requires 3 capacitors: input, output and fly capacitor, and a 1 µF value is typically recommended. For the input capacitor, a larger value of 2.2 µF or 4.7µF will help reduce input volt- age 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 capacitors is included in Table 1. The input and output capacitors should be located as close to the V IN and VOUT pins 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 SP6685. The fly capacitor should be located as close as possible to the C1 and C2 pins as possible. 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) Part Reference Part Number Value Size Manufacturers/ Website U1 SP6685ER 3x3mm DFN - 10 pin Sipex/www.sipex.cpm CIN GRM188R0J475KE19 4.7uF/6.3V 0603/X5R/0.9mm ht Murata/www.murata.com COUT, CF GRM155R60J105KE19B 1uF/6.3V 0402/X5R/0.5mm ht Murata/www.murata.com RSET - 88.7K 0402 any RSENSE - 0.22ohms 0603 any |
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