AL5809 datasheet(6/16 Pages) DIODES

6 / 16 page

AL5809

Document number: DS36625 Rev. 5 - 2

6 of 16

www.diodes.com

December 2016

AL5809

Application Information (continued)

PWM Dimming

The AL5809 can be used to provide LED current dimming driving the Out pin via the MOSFET switch to ground (Figure 4a) applying a PWM

signal with a frequency range between 100Hz and 200Hz. The Out pin current is then effectively switched on and off to modulate the output LED

current. The dimming effect can be achieved by varying the PWM signal duty cycle.

VIN

PWM_DIM

(ZXMN6A11Z)

OUT

AL5809

PWM Dimming by External MOSFET

OUT

VIN

ON/OFF

Switch

AL5809

PWM Dimming by Power Supply VIN ON/OFF

Figure 4 PWM Dimming

Recommended PWM Frequency and Dimming Range

PWM Frequency (Hz)

Duty Cycle (%)

Min

Max

100

200

Test conditions (Figure 4a): PWM frequency 100Hz

–200Hz Square wave, 0-4V gate voltage, VIN = 6V, 1 LED, AL5809-30mA

Use the following formula to calculate the Min and Max duty cycle:

Min. Duty cycle (%) = (tON_MIN) / (time period of the PWM signal)

Max. Duty cycle (%) = 100% - ((tOFF_MIN) / (time period of the PWM signal))

Notes: tON_MIN = 0.5mS (Min. value), and tOFF_MIN = 0.5mS (Min. value) are listed in the Electrical Characteristics table on page 4.

AL5809 Datasheet(PDF) 6 Page - Diodes Incorporated