As stated earlier, the best method to provide a large dimming range is using low frequency pulse width modulation on the ADJ pin. Low frequency PWM control turns the LED off and on and the average current in the LED is controlled. To avoid visible flicker, the frequency should be greater than 100 Hz, typical frequencies used are between 200 to 500 Hz. Using higher frequencies and the ZXLD1350 internal low pass filter will start to have an influence which may limit the dimming range. 1 to 100% dimming range is easily achievable with a simple circuit such as a micro-controller or the 555 timer circuit. A DC voltage or high-frequency PWM signal can also be used, but this will only give a maximum brightness control from over a range of 6 to 1. One other thing to watch for reverts back to your choice of inductor and dimming frequency. This audible frequency range may cause the inductor to act like a small loud speaker producing a buzzing noise at the dimming frequency.