Figure 5-14, Figure 5-15 show the hybrid dimming waveforms at 10%, and 20% duty cycles, respectively. Input voltage is 48 V, with 7 white LEDs in series used as load. The full-scale LED current is set at 4 A. The ADIM/HD pin is always low. The frequency of the input PWM signal at the PWM/EN pin is 20 kHz.

Figure 5-11 Waveforms at 10% Duty Cycle, 20 kHz Hybrid Dimming

Figure 5-12 Waveforms at 20% Duty Cycle, 20 kHz Hybrid Dimming

When the hybrid dimming is enabled, the LED current is regulated by the analog dimming at high brightness level (12.5% ~ 100%) and by the PWM dimming at low brightness level (0%~12.5%).

Figure 5-13 gives the test result of linearity of hybrid dimming, in comparison with the theoretical value. Input voltage is 48V, with 7 white LEDs in series used as load. The full-scale LED current is set at 4 A. The frequency of the input PWM signal at the PWM/EN pin is 20 kHz.

Figure 5-13 Hybrid Dimming Linearity