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SP6682 Datasheet(PDF) 6 Page - Sipex Corporation |
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SP6682 Datasheet(HTML) 6 Page - Sipex Corporation |
6 / 12 page 6 Date: 5/5/04 SP6682 High Efficiency Charge Pump Regulator for White LEDs © Copyright 2004 Sipex Corporation encing high input voltages. Another important operation of this block is the PWM/EN dim- ming control, which is implemented in the delay of each pump driver, so that the enable high pulse width is proportional to the delay of the individual pump switches. 5) VOUT Comparator and Output Control. A 306mV reference voltage is compared to feed- 1 8 5 Rb SP6682 Rb 2.2uF GND FB V OUT Figure 9. Driving discrete white LEDs as current source Configuring the SP6682 as Voltage or Current Source The white LED load configuration used by customers can be discrete white LEDs or a white LED module. Inside the white LED module, there may or may not be resistors in series with the white LEDs. According to the different application requirements, the SP6682 can be configured as either a voltage source or a current source to provide solutions for these different applications, as shown in figure 9~12. Figure 9 shows using the SP6682 to drive discrete white LEDs as a current source. The current in one white LED current is set by the ratio of the feedback pin voltage (306mV) and the bias resistor RB. To set the operating current, RB can be selected by: RB = VFB ILED 3-wire W-LED module Anode FB GND Fig 10. 3-wire white LED module The current of the remaining white LEDs is set according to the similarity of the white LEDs. 3- wire white LED module with internal series resistors as shown in figure 10 can also be driven in this way. GND V OUT Anode 5 V FB Rb SP6682 Cathode 8 2-wire W-LED module 1 Figure 11. Driving 2-wire white LED module as current source OPERATION: Continued back output voltage to control the Vout needed for the application. Output current is set by a bias resistor from FB pin to GND pin chosen by the relationship: IOUT = VFB RFB where VFB = 306mV. In figure 11, SP6682 was used to drive a 2-wire white LED module without internal series resis- tors as a current source. The bias resistor RB is selected to regulate the total current of the white LED module instead of the current of single LED as in figure 9. APPLICATION INFORMATION |
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