LED backlighting is becoming a boom and flooding people's lives. From the debut of LED-backlit notebooks in 2008 to the gorgeous debut of LED-backlit LCD TVs in 2009, it has attracted people's attention. For LED backlights of medium and large size displays, several technical problems must be solved. The most direct problem is the consistency of the brightness between LEDs. The number of backlight LEDs required for medium and large size displays is up to tens to thousands. If the brightness of the LEDs is inconsistent, the backlight will be different, which will seriously affect the display.
We know that the brightness of an LED is determined by the current flowing through the LED, so the way to ensure that the brightness of the LED is the same is to ensure that the current flowing through all the LEDs is exactly the same. This means that in the case of multiple LED backlights, the series connection method is better than the parallel mode to achieve the uniformity of the illumination brightness. In this case, it is important to control the current accuracy of the LED string to ensure that the brightness of the backlight LED string between the customer's product and the product is consistent.
But the number of LEDs connected in series is unlikely to be too much. At normal illumination, the voltage drop across the white LED is approximately 3.5V, meaning that the voltage drop across 10 phases can be as high as 35V. For the 14" display, the number of LEDs required is more than 40. If all are connected in series, the voltage drop will reach about 140V or higher, not to mention the larger display. So, centering, In the case of large-size displays, the way of full series connection is unrealistic and must be combined in series and parallel. When the system drives the backlight LED string in this way, it is not always possible to achieve accuracy requirements for each current. To ensure the backlight effect, ±1% current accuracy means that the maximum difference between the two channels can reach 2%. Unless the current accuracy index is exceptionally high, it is necessary to limit the current difference between the paths. Current matching is often used to indicate the maximum level of difference between multiple parallel outputs on the same system.
Its definition is as follows:
Imatch = (Imax-Imin)/Iavg*100%
That is, the difference between the maximum value and the minimum value of each current and the percentage of each path average.
Because the LED backlight of the medium and large size display has the above basic requirements, a special LED driver chip is needed to help the system realize the driving management of the backlight LED, simplify the system design, and provide more control and protection functions. The latest PT4112 from China Resources Converse Technology is such a product.
PT4112 technical features
The PT4112 is a 6-channel white LED driver IC with up to 10 white LEDs in series, so a single chip can drive up to 60 white LEDs. The PT4112 not only has excellent current accuracy and current matching, ideal conversion efficiency, and wide operating voltage range, but also integrates rich control functions and comprehensive protection functions. The main functions and technical features of the PT4112 are as follows:
1. Ultra high precision. Using patented design technology and advanced analog process technology, PT4112's current accuracy is up to ±2%, and the current matching between 6 channels can be as high as ±1.5%, which is not only second to none in local original products, but also fully meets High-end notebooks require such high image quality applications.
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