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LP3310B6F Datasheet(PDF) 6 Page - Lowpower Semiconductor inc |
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LP3310B6F Datasheet(HTML) 6 Page - Lowpower Semiconductor inc |
6 / 9 page ![]() LP3310-00 Jan.-2018 Email: marketing@lowpowersemi.com www.lowpowersemi.com Page 6 of 9 Preliminary Datasheet LP3310 Dimming control a. Using a PWM Signal to EN Pin For controlling the LED brightness, the LP3310 can perform the dimming control by applying a PWM signal to EN pin. The internal soft-start and wide range dimming frequency from 100Hz to 100KHz can insignificantly reduce audio noise when dimming. The average LED current is proportional to the PWM signal duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of EN pin, in order to let the dimming control perform correctly. VIN EN NC LX 6 4 1 5 2 GND LED+ VIN 4.7uH C2 2.2uF R1 12Ω C1 10uF FB 3 LED- PWM R5 100KΩ D1 b. Using a DC Voltage Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming control using a DC voltage circuit is shown in below. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to VFB increases and the voltage drop on R2 decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V, the selection of resistors in below sets dimming control of LED current from 20mA to 0mA. VIN EN NC LX 6 4 1 5 2 GND LED+ VIN 4.7uH C2 2.2uF R1 12Ω C1 10uF FB 3 LED- VDC EN R2 5.1KΩ R3 68KΩ R5 100KΩ D1 c. Using a Filtered PWM signal Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. A filtered PWM signal acts as the DC voltage to regulate the output current. The suggested application circuit is shown in the below. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2.8V PWM signal should be above 2KHz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get different output current. According to the application circuit of below, output current is from 35mA to 12mA by adjusting the PWM duty cycle from 10% to 90%. VIN EN NC LX 6 4 1 5 2 GND LED+ VIN 4.7uH C2 2.2uF R1 12Ω C1 10uF FB 3 LED- PWM EN R2 6.8KΩ R3 56KΩ R4 100KΩ C3 0.1uF R5 100KΩ D1 |
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