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SP6683 Datasheet(PDF) 4 Page - Sipex Corporation |
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SP6683 Datasheet(HTML) 4 Page - Sipex Corporation |
4 / 10 page 4 Date: 07/07/04 SP6683 White LEDs Driver for Parallel Configuration © Copyright 2004 Sipex Corporation 4) VOUT Comparator and Output Control. A 306mV reference voltage is compared to feed- 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. Configuring the SP6683 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 SP6683 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 SP6683 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 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 1 8 5 Rb SP6683 Rb 1uF GND FB V OUT Figure 9. Driving discrete white LEDs as current source General Overview The SP6683 is a current regulated charge pump ideal for converting a Li-Ion battery input for driving white LEDs used in backlighting color displays in cellular phones, PDAs, digital cam- eras and MP3 players. The SP6683 is able to efficiently drive up to eight 20mA white LEDs in parallel and maintain a constant brightness over a very wide operating voltage range (2.7V to 5.5V). The SP6683 operates with an internal 1.2MHz clock, enabling the use of small exter- nal components. Other features of SP6683 in- clude PWM dimming control as well as com- plete input/out disconnect in shutdown. In shut down mode the IC draws less than 1.5 µA cur- rent. The output regulation is achieved by sens- ing the voltage at the feedback pin and modulat- ing the switch between the charge pump and output capacitor. Theory of Operation The SP6683 regulated charge pump block dia- gram consists of four main blocks (Voltage Reference, Mode Control, Clock Manager, Start- up and Charge-Pump Switches) and two com- parators (VMODE Comparator and VOUT Com- parator). 1) Voltage Reference. This block provides the 306mV and 1.25V reference voltages needed for the two comparators. 2) Mode Control. An external voltage divider connected to the VMODE pin will define an input voltage to the mode comparator which sets the logic state of the mode selection outputs to the X1 or X1.5 modes. VMODE is compared to a 1.25V bandgap voltage. For example, if one makes a 158K/100K divider, the mode will change at 2.58 x 1.25 V =3.23V. A comparator- based cycle by cycle regulation ensures that no mode change occurs during cycles. 3) Clock Manager. An internal 1.2MHz clock is generated in this block. Depending on the mode control, the appropriate clock phasing is generated here and sent to the start-up and charge-pump switches block. OPERATION |
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