AL1672

Document number: DS39344 Rev. 1 - 2

9 of 14

www.diodes.com

July 2017

© Diodes Incorporated

AL1672

0

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100

0

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PWM Duty(%)

According to these above formulas, the mean output current can be induced finally by below expressions.

_

2

REF

O MEAN

CS

V

I

R





------------------------------------------------ (7)

to 0.3V; Therefore, the constant output current control can be realized with appropriate parameter design.

Dimming Mode

The AL1672 can support two dimming modes: analog dimming and PWM dimming.

1. Analog Dimming Mode

In analog dimming mode, the dimming signal is added to APWM pin directly to realize dimming function. The setting circuit is shown as figure 2. A

switch will be turned off and the output current drops to zero. The dimming curve is shown as figure 3 and the dimming range is from 18% to

100%.

APWM

AL1672

0.3-2.4V

Dimming signal

Figure 2: Analog Dimming Setting Circuit

Figure 3: Analog Dimming Curve

2. PWM Dimming Mode

In PWM dimming mode, dimming signal will be added to APWM pin .The setting circuit is shown as figure 4. The output current is chopped by the

dimming signal directly. The logic high level of the dimming signal need to be higher 2.4V while the logic low level is lower than 0.3V.Switch is turn

off at logic low level. The dimming curve is shown as figure 5. The dimming range can be 100 to 1% with 1kHz frequency of PWM signal.

APWM

PWM dimming signal

AL1672

Figure 4: PWM Dimming Setting Circuit

Figure 5: PWM Dimming Curve (PWM frequency is 1 KHz)

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V