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SP6691ER Datasheet(PDF) 9 Page - Sipex Corporation |
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SP6691ER Datasheet(HTML) 9 Page - Sipex Corporation |
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9 / 15 page  Jun26-07 Rev D Micro Power Boost Regulator Series White LED Driver © 2007 Sipex Corporation Output Voltage Program The SP6691 can be programmed as either a voltage source or a current source. To program the SP6691 as voltage source, the SP6691 re- quires 2 feedback resistors R1 & R2 to control the output voltage. As shown in Figure 22. Table 4. Divider Resistor Selection Brightness Control Dimming control can be achieved by applying a PWM control signal to the SHDN pin. The brightness of the white LEDs is controlled by increasing and decreasing the duty cycle of the PWM signal. A 0% duty cycle corresponds to zero LED current and a 100% duty cycle corre- sponds to full load current. While the operating frequency range of the PWM control is from 60Hz to 700Hz, the recommended maximum brightness frequency range of the PWM signal is from 60Hz to 200Hz. A repetition rate of at least 60Hz is required to prevent flicker. The magnitude of the PWM signal should be higher than the minimum SHDN voltage high. Open Circuit Protection When any white LED inside the white LED module fails or the LED module is disconnected from the circuit, the output and the feedback control will be open, thus resulting in a high output voltage, which may cause the SW pin voltage to exceed it maximum rating. In this case, a zener diode can be used at the output to limit the voltage on the SW pin and protect the part. The zener voltage should be larger than the maximum forward voltage of the White LED module. APPLICATION INFORMATION: Continued L1 1.22V R2 D1 C1 C2 R1 VOUT U1 SP6691 1 2 3 4 5 SW G ND FB SHDN V IN VIN Figure 22. Using SP6691 as Voltage Source The formula and table for the resistor selection are shown below: R1 = ( VOUT - 1 ) • R2 1.22 precision resistors are recommended. Table 3 below shows the Rb selection for different white LED currents. For example, to set the operating current to be 20mA, Rb is selected as 60.4 , as shown in the schematic. Table 3. Bias Resistor Selection IF (mA) Rb ( ) 5 243 10 121 12 102 15 80.6 20 60.4 VOUT (V) R1 ( ) R2 ( ) 12 1M 113K 15 1M 88.7K 18 1M 73.2K 21 1M 61.9K 30 1M 42.2K |
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