AL3050

Document number: DS38578 Rev. 2 - 2

9 of 16

www.diodes.com

July 2016

© Diodes Incorporated

AL3050

Where

LED

I

= full-scale output current of LEDs

FB

V

= 200mV (regulated voltage of FB)

SET

R

= current sense resistor at FB pin

The output current tolerance depends on the FB accuracy and the current sensor resistor accuracy.

6. LED Brightness Dimming Mode Selection

The CTRL pin is used for the control input for both dimming modes, PWM dimming and single wire dimming. The dimming mode for the AL3050 is

selected each time the device is enabled. The default dimming mode is PWM dimming. To enter the single wire mode, the following digital pattern

on the CTRL pin must be recognized by the IC every time the IC starts from the shutdown mode.

1. Pull CTRL pin high to enable the AL3050, and to start the single wire dimming detection window;

detection

window starts from the first CTRL pin low to high transition.

If all above three conditions are fulfilled, the IC enters single wire dimming mode, otherwise enters PWM dimming mode. Once the dimming mode

is programmed, it can not be changed without another start up. This means the IC needs to be shut down by pulling the CTRL low for 3.5ms and

restarts. See the Dimming Mode Detection and Soft Start (Figure 1) for a graphical explanation.

CTRL

FB

Duty*200mV

0mV

…

…

Startup

Delay

Shutdown

CTRL

Program code

200mV

100mV

0mV

FB

Program code

…

……

Shutdown

Figure 1. Dimming Mode Detection and Soft Start

7. PWM Dimming Mode

When the CTRL pin is constantly high, the FB voltage is regulated to 200mV typically. However, the CTRL pin allows a PWM signal to reduce this

regulation voltage; therefore, it achieves LED brightness dimming. The relationship between the duty cycle and FB voltage is given by Equation 2.

mV

Duty

V

FB

200





(2)

Where

Duty = duty cycle of the PWM signal

200mV = internal reference voltage