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SP6685 Datasheet(PDF) 13 Page - Sipex Corporation |
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SP6685 Datasheet(HTML) 13 Page - Sipex Corporation |
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13 / 16 page  13 Date: 7/6/06 Rev B SP6685, 700mA Buck/BoostCharge Pump LED Driver © 2006 Sipex Corporation COMPONENT SELECTION 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 to the C1 and C2 pins as possible. See typical circuit layout (page 13) for details on the recommended layout. To obtain lower output ripple, the C OUT value can be increased from 1μF to 2.2μF or 4.7μF with a corresponding decrease in output ripple as shown in the Typical Performance Characteristic curves. For output currents of 500mA to 700mA, the recommended C FC fly capacitor value of 1μF should be used. Out- put currents in Flash of 100mA to 400mA can use a 0.47μF C FC but a minimum 1μF C OUT is still needed. _______________________ RESISTOR 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) 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) For an example of 200mA Torch mode and 600mA Flash mode, the values R SENSE = 0.25Ω, V FB = 150mV (Flash Mode), and RSET = 94KΩ 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 power can be calculated and resistor size selected. The R SENSE resistor is recom- mended to be size 0603 for most applica- tions. The range of typical resistor values and sizes are shown here in Table 2. Table 2: Resistor values and sizes Part Reference Value Tolerance Size Manufacturers RSET 68k 5% 0402 any RSET 75k 5% 0402 any RSET 82k 5% 0402 any RSET 91k 5% 0402 any RSET 100k 5% 0402 any RSET 110k 5% 0402 any RSET 120k 5% 0402 any RSET 130k 5% 0402 any RSET 140k 5% 0402 any RSET 150k 5% 0402 any RSENSE 0.22 5% 0603 Panasonic or Vishay RSENSE 0.27 5% 0603 Panasonic or Vishay RSENSE 0.33 5% 0603 Panasonic or Vishay RSENSE 0.39 5% 0603 Panasonic or Vishay RSENSE 0.47 5% 0603 Panasonic or Vishay |
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