AL1792 datasheet(4/18 Pages) DIODES

4 / 18 page

AL1791/1792/1793/1794

Document number:37957 Rev. 3 - 2

4 of 18

www.diodes.com

September 2015

AL1791/1792/1793/1794

Detailed Description (continued)

LED Current Setting and Current Ratio

The AL1792 and AL1793 are designed to have an equal-sized channel current ratio for all channels, while the AL1794 is equipped with ratio-

optimized current sinks. The current ratio is predetermined and facilitated for Tunable Color or Tunable White applications. The absolute current

levels can be adjusted externally with RSET resistor. The LED current is expressed as below:

For AL1791:

For AL1792:

For AL1793:

For AL1794:

For example, when an RSET of 12KΩ is used, Channel 1, 2, 3, and 4 of AL1794 provide a current of 250mA, 250mA, 187.5mA, and 62.5mA

respectively. For the same RSET setting, each channel of AL1792 and AL1793 provides same current amount of 250mA. AL1791 provides 500mA

for the same RSET setting.

The maximum LED current for Channel 1 can be adjusted up to 500mA via RSET resistor. The other channels will provide current levels with the

same predetermined ratio. Any two or more channels can be tied together to drive one LED string with aggregated current. So when current

needed for any channel is greater than the maximum value the device can provide, two or more channels or devices can be paralleled together to

provide the drive current needed.

PWM Dimming Control

When any one of the PWMx pins is connected to PWM signals with frequency ranging from 500Hz and above during startup, the device is

determined in PWM dimming mode. In this mode, a high level of PWM signal will turn on the current sink to flow through the LED and low level will

turn it off. Consequently, the LED current and LED brightness of each corresponding channel can be adjusted.

The pulse width of the PWM signa

l is recommended to be greater than 2.5μS to support down to 0.25%@1KHz deep dimming capability still with

good linearity. Further deeper dimming through higher frequency PWM signals is possible, which maintains reasonable linearity - 0.1%@1KHz,

0.4%@4KHz, or 1.0%@10KHz. PWM signals can be driven static low or high to turn off or on the corresponding channels constantly.

AL1792 Datasheet(PDF) 4 Page - Diodes Incorporated