AL1771/1772

Document number: DS41314 Rev. 1 - 2

14 of 24

www.diodes.com

August 2018

© Diodes Incorporated

AL1771/1772

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Channel 1

Channel 2

Total IC Current

AL1771

300mA

Not Applicable

300mA

AL1772

150mA

150mA

300mA

Table 2. Recommended Minimum Channel Current and Total IC Current for AL1771/1772

Along with bus-mode fault reporting, multiple devices can be employed together to increase current driving capability or channel count versatility.

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.

3.

High Performance PWM Dimming

(1)

Support High Frequency e-Flicker Free Dimming

For PWM-dimmed Light Sources, there are two important performance aspects to pay attention, namely, PWM frequency and deep dimming

performance. While human eyes could not discern any flickering caused by PWM-dimming light sources over 200Hz, Electronic devices such as

camera for smartphones could detect flickering (referred as e-Flicker) caused by certain much higher PWM-dimmed light sources. Generally

speaking, the higher the PWM dimming signals applied to the light source, the less visible e-Flicker detected by electronic components.

The AL1771/1772 provides PWM dimming control. The PWM frequency is recommended to be greater than 500Hz. For e-Flicker free operation,

4kHz or higher frequency is recommended. High level of PWM signal will turn on the current sink to flow through the LED and low level of PWM

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

(2)

Deep Dimming Capability

Measured light is linearly proportional to the measured current and PWM duty cycle. The perceived light by human eyes has a non-linear

relationship with measured light. Human eyes are also found to be more sensitive to low light situations. For example, 10% measured light is

perceived to be 32% of the original full light. 5% measured light is perceived to be 22% of the original full light. 1% measured light is perceived to

be 10% of the original full light. Therefore, deep dimming capability is required to save significant energy as well as to provide adequate visible

light output.

The pulse width of PWM signal applied to AL1771/1772 can be as low

as 1μs to support down to 0.1%@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.

4.

Low-Power Mode and Adaptive Thermal Management (ATM)

(1)

Automatic Entrance/Exit to/ from Low-Power Mode

For SCL applications, the brightness and CCT tuning are done through LED emitter light mixing by changing average current through associated

PWM signal of each emitter channel. When no PWM signal is detected by the Linear LED driver, it will automatically enter the low-power mode for

Ω (for 500mA channel current

requirement for SCL bulbs, this power saving is very significant.

When any PWM signal is detected, the Linear LED driver will automatically exit the low power mode and perform it designated functions properly.

(2)

Adaptive Thermal Management (ATM) Scheme

headroom (VLED_REG). On the other hands, excessive voltage headroom provided needs to be absorbed by AL1771/1772, which increases heat

dissipation to complicate thermal management. Power Good reporting serves as a mechanism to detect the LED power supply condition and

adjust the supply voltage to LEDs through AC-DC voltage feedback in order to minimize unnecessary overdrive voltage to the LED Driver and

optimize the efficiency.