移动背光的LED驱动器解决方案

移动背光的LED驱动器解决方案 　　移动设备，包括智能手机，平板电脑和笔记本电脑，已广泛采用LED背光系统，由于其低功耗，能源效率，以及小型和超薄包装。尽管广泛采用（也许因为它），LED驱动制造商继续提高他们的设备，以进一步提高能源效率和电池寿命的移动产品，并提高用户体验。 　　LED驱动器制造商正在研究用户如何与他们的移动设备接口，特别是智能手机和平板电脑，开发电力产品，提供最佳的照明，以及更高的效率。一个很好的例子，他们想出的是德克萨斯仪器lm3697，可驱动三个并联的高压LED串的显示和键盘照明。该设备的最显着的特点是其11位可配置的调光分辨率，显着提高了用户的显示照明。 　　 　　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.”