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SP6685 Datasheet(PDF) 12 Page - Sipex Corporation |
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SP6685 Datasheet(HTML) 12 Page - Sipex Corporation |
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12 / 16 page  12 Date: 7/6/06 Rev B SP6685, 700mA Buck/BoostCharge Pump LED Driver © 2006 Sipex Corporation When in Flash mode, (Flash = V IN), the FB regulation voltage is set by the resistor R SET connected between the R SET pin and SGND and the equation: V FB = (1.26V/ RSET)*11.2KΩ (Flash Mode) Where 1.26V is the internal bandgap refer- ence voltage and 11.2KΩ is an internal resistance used to scale the R SET current. Typical values of R SET are 40KΩ to 180KΩ for a range of V FB = 300mV to 75mV in Flash mode. The output current is then set in either Flash or Torch mode by the equation: I OUT = VFB / RSENSE THEORY OF OPERATION ______________ OVERTEMPERATURE PROTECTION When the temperature of the SP6685 rises above 145 degrees Celsius, the over tem- perature protection circuitry turns off the output switches to prevent damage to the device. If the temperature drops back down below 135 degrees Celsius, the part auto- matically recovers and executes a soft start cycle. ___________________ OVERVOLTAGE PROTECTION The SP6685 has over voltage protection. If the output voltage rises above the 5.5V threshold, the over voltage protection shuts off all of the output switches to prevent the output voltage from rising further. When the output decreases below 5.5V, the device resumes normal operation. ___________________OVERCURRENT PROTECTION The over current protection circuitry moni- tors the average current out of the V OUT = 50mV (Torch Mode) pin. If the average output current exceeds approximately 1Amp, then the over current protection cir- cuitry shuts off the output switches to pro- tect the chip. _____________________COMPONENT SELECTION The SP6685 charge pump circuit requires 3 capacitors: 4.7μF input, 1μF output and 1μF fly capacitor are typically recommended. 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 sur- face mount ceramic for low lead inductance necessary at the 2.4MHz switching frequency of the SP6685 and to obtain low ESR, which improves bypassing on the input and output and improves output voltage drive by reduc- ing output resistance. Ceramic capacitors with X5R or X7R temperature grade are recommended for most applications. A se- lection of recommended capacitors is in- cluded in Table 1 below. Manufacturers Website Part Number Capacitance/ Voltage Capacitor Size/Type/Thickness ESR at 100KHz TDK/www.tdk.com C1005X5R0J105M 1uF/6.3V 0402/X5R/0.5mm 0.03 TDK/www.tdk.com C1608X5R0J475K 4.7uF/6.3V 0603/X5R/0.9mm 0.02 TDK/www.tdk.com C2012X5R0J106M 10uF/6.3V 0805/X5R/1.35mm 0.02 Murata/www.murata.com GRM155R60J105KE19B 1uF/6.3V 0402/X5R/0.55mm 0.03 Murata/www.murata.com GRM188R60J475KE19 4.7uF/6.3V 0603/X5R/0.9mm 0.02 Murata/www.murata.com GRM21BR60J106KE19L 10uF/6.3V 0805/X5R/1.35mm 0.02 Table 1: Recommended Capacitors |
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