DLPS039F December 2015 – April 2019 TPS99000-Q1
When operating in discontinuous mode, two methods of dimming are used concurrently to reduce brightness of the display:
Figure 25 is an example of the brightest LUT data table having 8 pulses per LSB (smallest bit slice). The LED pulse height is modulated to achieve a 2:1 dimming ratio while still maintaining 8 pulses per LSB. To allow for a seamless transition to lower dimming levels, a change to 4 pulses per LSB plus higher LED amplitude is made as illustrated in Figure 26. The total light generated in both cases in Figure 26 is approximately equal. A system calibration is used to determine this ½ LED amplitude photo feedback DAC setting.
As a smooth dimming (brightness going down) sequence continues, the process above eventually results in using a 1 pulse per LSB. Amplitude dimming is used to dim to the absolute minimum display brightness level as illustrated in Figure 27.
As shown in Figure 27, once a single pulse-per-LSB is selected, all remaining dimming must occur using only pulse height threshold reduction.