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W-6137 Scheda tecnica(PDF) 9 Page - Copal Electronics |
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W-6137 Scheda tecnica(HTML) 9 Page - Copal Electronics |
9 / 16 page W-6137 9 Device Operation The W-6137 is a fixed frequency (1 MHz), low noise, inductive boost converter providing constant current to the load. A high voltage internal CMOS power switch is used to energize the external inductor. When the power switch is then turned off, the stored energy inductor is released into the load via the external Schottky diode. The on/off duty cycle of the power switch is internally adjusted and controlled to maintain a constant regulated voltage of 0.3 V across the external feedback resistor connected to the feedback pin (FB). The value of external resistor will accurately set the LED bias current accordingly (0.3 V/R1). During the initial power-up stage, the duty cycle of the internal power switch is limited to prevent excessive in-rush currents and thereby provide a “soft-start” mode of operation. While in normal operation, the device will comfortably deliver up to 30 mA of bias current into a string of up to 5 white LEDs. In the event of a “Open-Led” fault condition, where the feedback control loop becomes open, the output voltage will continue to increase. Once this voltage exceeds 24 V, an internal protection circuit will become active and place the device into a very low power safe operating mode. In addition, an internal clamping circuit will limit the peak output voltage to 29 V. If this fault condition is repaired, the device will automatically resume normal operation. Thermal overload protection circuitry has been included to prevent the device from operating at unsafe junction temperatures above 150 C. In the event of a thermal overload condition the device will automatically shutdown and wait till the junction temperatures cools to 130 C before normal operation is resumed. Enable Current Sense 300 mV R1 15 C1 Thermal Shutdown & UVLO 1MHz Oscillator Over Voltage Protection PWM & Logic Driver C2 GND SW FB + – + – VIN VIN VREF SHDN RC CC RS N1 Figure 23. Block Diagram VOUT ILED A1 A2 |
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