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TD8201 Datasheet(PDF) 9 Page - TECHCODE SEMICONDUCTOR, INC. |
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TD8201 Datasheet(HTML) 9 Page - TECHCODE SEMICONDUCTOR, INC. |
9 / 11 page ![]() December, 20, 2011 Techcode Semiconductor Limited www.techcodesemi.com 9 Techcode® White LED Step-up Converter TD8201 DATASHEET Function Description(Cont.) Dimming Control There are three different types of dimming control circuits: 1. Using a DC Voltage For some applications, the preferred method of brightness control is a variable DC voltage to adjust the LED current. The dimming control using a DC voltage is shown in Figure 3. As the DC voltage increases, the voltage drop on R2 increases and the voltage drop on R1 decreases. Thus, the LED current decreases. The selection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and much larger than the FB pin bias current. 2. Using a PWM Signal to EN Pin With the PWM signal applied to the EN pin, the TD8201 is turned on or off by the PWM signal. The LEDs operate at either zero or full current. The average LED current increases proportionally with the duty cycle of the PWM signal. A 0% duty cycle corresponds to zero LED current. A 100% duty cycle corresponds to full current. The frequency range of the PWM signal should be up to 100KHz 3. Using a Filtered PWM Signal The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC voltage source in dimming control. Board Layout Consideration As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To maximize efficiency, switch rise and fall times are made as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency switching path is essential. The voltage signal of the SW pin has sharp rise and fall edges. Minimize the length and area of all traces connected to the SW pin and always use a ground plane under the switching regulator to minimize interplane coupling. In addition, the ground connection for the feedback resistor R1 should be tied directly to the GND pin and not shared with any other component, ensuring a clean, noise‐free connection. |
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