AL3022

Document number: DS36514 Rev. 3 - 2

7 of 12

www.diodes.com

September 2014

© Diodes Incorporated

AL3022

3043

A Product Line of

Diodes Incorporated

Application Information

General Operation

The AL3022 uses a constant frequency, voltage mode control scheme to provide excellent line and load regulation. To drive LED load, the AL3022

can be connected as shown in the Typical Applications Circuit on page 1. The maximum duty cycle of the PWM controller is limited to 90%. PWM

dimming input can be provided by an external control signal greater than 100Hz, duty ratio of 1% to 90%. In addition, analog dimming can be

provided by a DC signal ranged from 0.8V to 2.4V.

Enable/Dimming Control

The AL3022 uses EN pin to turn on and off the controller and also perform Digital (PWM) Dimming.

When EN input voltage is lower than 0.3V, the controller turns off and the shutdown current can be limited below 0.1µA. When EN input voltage is

higher than 2.6V, the controller turns on and the reference voltage is set to 0.2V.

The AL3022 has an internal 80±15%k

Ω pull low resistor on the EN pin, thus the device is normally in the off state or shutdown mode operation.

When a PWM signal was presented into the EN pin of the AL3022 shown in Figure 1 below.

1). When the EN pin is higher than 2.6V, the device will turn on and the output current is at the programmed maximum level.

2). When the EN pin is lower than 0.3V, the device will turn off and the output current goes to 0mA.

If the frequency of the PWM signal is greater than 100Hz, the human eye cannot detect the on and off state of the LEDs. The human eye can only

see a dimmed diode rather than a pulsed brightness. This dimming method provides a controlled inrush current at turn-on. The PWM duty cycle

from 0% to 100% controls the output current from 0mA to the maximum programmed level.

AL3022

FB

EN

R

PWM

Figure 1. Digital Dimming Control Using a PWM Signal in EN Pin

Analog Dimming Control

The Analog Dimming is to inject a constant DC voltage to EN pin shown in Figure 2 below. The feedback voltage is indirectly adjusted when the

EN pin voltage is from 0.8V to 2.4V, which can be used as dimming control. The output LED current can be adjusted from minimum to maximum

level by applying the DC voltage level from 0.8V to 2.4V.

Comparing with all kinds of dimming control, this method features a best output voltage and LEDs current.