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W-6139TD-GE Arkusz danych(PDF) 8 Page - Copal Electronics |
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W-6139TD-GE Arkusz danych(HTML) 8 Page - Copal Electronics |
8 / 13 page W-6139 8 Device Operation The W-6139 is a fixed frequency (1 MHz), low noise, inductive boost converter that provides a constant current with excellent line and load regulation. The device uses a high voltage CMOS power switch between the SW pin and ground to energize the inductor. When the switch is turned off, the stored energy in the inductor is released into the load via the 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 feedback resistor connected to the feedback pin (FB). The value of the resistor sets the LED 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. In the event of an “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. 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. Application Information External Component Selection Capacitors The W-6139 only requires small ceramic capacitors of 4.7 F on the input and 1 F on the output. Under normal condition, a 4.7 F input capacitor is sufficient. For applications with higher output power, a larger input capacitor of 10 F may be appropriate. X5R and X7R capacitor types are ideal due to their stability across temperature range. Inductor A22 H inductor is recommended for most of the W-6139 applications. In cases where the efficiency is critical, inductances with lower series resistance are preferred. Inductors with current rating of 800 mA or higher are recommended for most applications. Sumida CDRH6D28 220 22 H inductor has a rated current of 1.2 A and a series resistance (D.C.R.) of 128 m typical. Schottky Diode The current rating of the Schottky diode must exceed the peak current flowing through it. The Schottky diode performance is rated in terms of its forward voltage at a given current. In order to achieve the best efficiency, this forward voltage should be as low as possible. The response time is also critical since the driver is operating at 1 MHz. Central Semiconductor Schottky rectifier CMSH1 40 (1 A rated) is recommended for most applications. LED Current Setting The LED current is set by the external resistor R1 connected between the feedback pin (FB) and ground. The formula below gives the relationship between the resistor and the current: R1 0.3 V LED current Table 5. RESISTOR R1 AND LED CURRENT LED Current (mA) R1 ( ) 20 15 25 12 30 10 100 3 300 1 |
Podobny numer części - W-6139TD-GE |
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Podobny opis - W-6139TD-GE |
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