移動背光的LED驅動器解決方案

　　移動設備，包括智能手機，平板電腦和筆記本電腦，已廣泛采用LED背光系統，由于其低功耗，能源效率，以及小型和超薄包裝。盡管廣泛采用（也許因為它），LED驅動制造商繼續提高他們的設備，以進一步提高能源效率和電池壽命的移動產品，并提高用戶體驗。

　　LED驅動器制造商正在研究用戶如何與他們的移動設備接口，特別是智能手機和平板電腦，開發電力產品，提供最佳的照明，以及更高的效率。一個很好的例子，他們想出的是德克薩斯儀器lm3697，可驅動三個并聯的高壓LED串的顯示和鍵盤照明。該設備的最顯著的特點是其11位可配置的調光分辨率，顯著提高了用戶的顯示照明。

　　An older， but still valuable product series is Intersil’s ISL97692/3/4A backlight LED drivers， which improve energy efficiency while increasing battery life of tablets and mobile devices. These drivers feature output current phase shifting， which maximizes efficiency during PWM dimming while eliminating audible noise. As an added benefit， particularly for space-constrained applications， the drivers do not require any input voltage except from the battery， helping to reduce board size and component count.

　　Let’s now take a closer look at Texas Instruments’ LM3697 11-bit LED driver. This device has several significant features. The first one is the 11-bit exponential dimming. This provides a more pleasing display brightness for the user because it provides 0.3 percent relative step size between brightness codes as the brightness level is ramped from one level to another level （Figure 1）。 “Because the human eye has a static contrast ratio of about 1 percent， the brightness of a display changing at 0.3 percent gives a very smooth brightness transition no matter how fast or slow the change happens，” says John Woodward， technical product marketing manager at Texas Instruments.

　　“The reason why the exponential ramp is important is because of the way the human eye senses light，” Woodward says. “A quick linear ramp is not very pleasing to the eye， but if you ramp exponentially and gradually turn it on at the lower levels first and then faster， your eye perceives that in a nice smooth transition. That is really why we ramp exponentially， to give the human eye a nice gradual response. You won’t see any flicker on the screen.”