Datasheet AL8116 (Diodes) - 10

AL8116 Functional Description and Application Information
(continued) OUT OUT 100% 100% Dimming Range Area Dimming Range Area VDIM_OFF_HYS a a er er A A yt yt u u D D or or e e Minimum Z Z Dimming Clamp 1.3V 1.4V VDIM 10.2V 1.5V VDIM 10.2V a. VCLAMP<4.2V b. VCLAMP≥4.2V
Figure 3. AL8116 Dimming Curve Dimming Performance 1) 0 to 10V Potential Dimming
When the input signal of DIM pin is a DC voltage, the AL8116 will transfer the DC potential to a PWM signal output at OUT pin. The frequency of output PWM on OUT pin is around 1.5kHz. Typical dimming curve is shown in Figure 3.
2) PWM Dimming
When the input signal of DIM pin is a PWM signal, the AL8116 will output a PWM signal at the OUT pin. The output frequency and duty of OUT pin follows the input PWM signal. The high level of input PWM signal on DIM pin must be higher or equal to 3.2V and the low level must be less than 1.2V. And the recommended PWM frequency range is from 500Hz to 5kHz. The AL8116 will switch to PWM dimming mode when the PWM rising slew rate of DIM pin signal is faster than 3V/µs through 1.2V to 3.2V and continues for 8 cycles. If PWM rising slew rate of DIM pin is larger than 3 V/µs, the AL8116 will reset internal cycles counter. Once entering PWM dimming mode, the AL8116 will continuously work at this mode until a new VCC UVLO cycle begins.
3) Potentiometer Dimming
When DIM pin is connected with a potentiometer to GND, the bias current source of DIM pin will flow through this potentiometer and generate a DC voltage on DIM pin, the AL8116 will transfer the resistance of potentiometer to a PWM signal output at OUT pin. The frequency of PWM signal on OUT pin is around 1.5kHz.
Internal Over Temperature Protection
When internal over temperature protection threshold is triggered (+135°C typ), the OUT pin of the AL8116 is then open drain. This protection will be auto-recovery after internal temperature goes down to a normal operating temperature.
Opto-Coupler Selection Guide
In the majority of applications, the dimming signal needs to be isolated from the rest of the application circuitry. An opto-coupler is often used to implement functional and reinforced isolation. Opto-couplers are excellent choices since they are very cost-effective and able to comply with virtually all safety standards. The most common and cost-effective opto-couplers are four-pin devices consisting of a LED and a photosensitive BJT, only collector and emitter of the photosensitive BJT are connected to the pins of the device. This character limits the device performance, especially switching times. Six-pin devices with the base of the BJT connected to a pin are seen less often. With use of these six-pin devices, the bandwidth of the transmission can be improved if necessary. Finally, there are high-speed digital couplers available, they are designed for very high data rates and offer a buffered output with a nearly perfect PWM signal. While offering superior performance, high speed couplers are considerably more expensive than simple LED-BJT couplers. There are two parameters of an opto-coupler that are most important to use with the AL8116: the current transfer ratio CTR and the switching times tR and tF. AL8116 10 of 13 April 2020 Document number: DS42629 Rev. 2 - 2
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