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SP6687ER1-L Datasheet(PDF) 5 Page - Sipex Corporation |
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SP6687ER1-L Datasheet(HTML) 5 Page - Sipex Corporation |
5 / 12 page 5 Date: 11/15/05 SP6687 4Channel Charge Pump White LED Driver © Copyright 2005 Sipex Corporation THEORY OF OPERATION The SP6687 is a high efficiency charge pump white LED driver. It provides 4 channels of low drop-out voltage current source to regulate the current for 4 white LEDs. For high efficiency, the SP6687 implements 3 modes of charge pump: x1/x1.5/x2 modes. An external RSET is used to set the current level of the White LEDs. SP6687 has an input current regulation circuit to reduce the input ripple. Soft Start The SP6687 includes a soft start circuit to limit the inrush current at power on and mode switching. The soft start circuit holds the input current level long enough for output capacitor COUT to reach a desired voltage level. When the soft start turns off, the SP6687 will not sink current spiking from VIN. Mode Decision The SP6687 uses a smart mode decision method to select the working mode for maximum efficiency. The mode decision circuit senses the output and LED voltage for up/down selection. Dimming Control CTRL0, CTRL1 and CTRL2 are used to control the on/off of correlated White LEDs. When an external PWM signal is connected to the control pin, the brightness of the white LEDs is adjusted by the duty cycle. The current flowing through White LEDs connected to the SP6687 can be set by RSET. Every current that flows through each respective White LED is 440 times greater than the current of RSET. The white LED current can be estimated by following equation: LED Current Setting where VISET =1.1V, and RSET is the resistance con- nected from ISET to GND. Thermal Shutdown The SP6687 provides a high current capability to drive 4 white LEDs. A thermal shutdown circuit is needed to protect the chip from thermal damage. When the chip reaches the shutdown temperature of 150ºC, the thermal shutdown circuit turns off the chip to prevent thermal accumulation in the chip. Overvoltage Protection SP6687 regulates the output voltage by controlling the input current. When the output voltage reaches the designated level, SP6687 reduces the input current. Subsequently, the output voltage regulation also serves as an overvoltage protection circuit. Short Circuit Protection A current limiting circuit is also included in the SP6687 for short circuit protection. Whenever the output sources a dangerously high current, the current limit- ing circuit takes over the output regulation circuit and reduces the output current to an acceptable level. ILED =440x ( VISET RSET ) APPLICATION INFORMATION Typical Application Circuit For 3-White LEDs EN CTRL0 CTRL1 CTRL2 C1P C1N C2P C2N GND LED1 LED2 LED3 LED4 C1 1µF C2 1µF 1 3 4 5 6 7 89 10 11 12 13 14 15 16 2 Li-ion Battery SP6687 VIN VOUT ISET RSET COUT 1µF CIN 1µF ® |
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