WHITE LED/OLED STEP-UP CONVERTER

FSP3304

2007-4-24

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To improve efficiency, resistors R2 and R3 can be connected as shown in Figure 4 to lower the effective feedback

voltage.

The following are dimming control methods for the FSP3304 series white LED application.

1. PWM Signal Driving SHDN

When a PWM signal is connected to the SHDN pin, the FSP3304 is turned on and off alternately under the control of

the PWM signal. The current through the LEDs is either zero or full scale. By changing the duty cycle of the PWM

signal (typically 1 kHz to 10kHz), a controlled average current is obtained.

2. DC Voltage Control

Figure 5 shows an application in which a DC voltage is used to adjust the LED current. The LED current increases

3. Filtered PWM Control

Figure 6 shows an application using a filtered PWM signal to control dimming.

4. Logic Control

A logic signal can be used to adjust the LED current in a discrete step, as shown in Figure 7.

Figure 4: Current setting for white LED application

Figure 5: DC voltage controlled dimming

Figure 6: Filtered PWM controlled dimming

Figure 7: Logic controlled dimming