Efficient, Flexible LED Backlighting Driver for Large LCD Screens

By Allan Lin, LED Lighting Business Unit Manager

Display screens are all around us—from smartwatches and tiny gadgets to the biggest flatscreen TVs. Demand continues to increase as more and more products add screens, with the automotive industry a significant part of this market growth.

The majority of these displays are based on liquid crystal display (LCD) technology. As LCDs themselves do not emit light, they require backlighting, which today is usually provided by white light-emitting diodes (LEDs). In many applications, LEDs have replaced the older option of cold cathode fluorescent (CCFL) backlights, mostly due to LEDs’ lower power consumption, smaller size, and greater reliability.

While organic light-emitting diode (OLED) technology has some significant advantages over LCD displays (such as better contrast), OLED screens are typically not as bright, and are generally more expensive.

LEDs need driver circuits to provide the right voltage and current, as well as to control the brightness of the LEDs. Dimming is typically controlled by modulating the driving signal at frequencies that are too high to be noticeable by users.

With a global market estimated at more than $2 billion[1] annually, the LED backlight display driver market is growing strongly. Design engineers are looking for display drivers and controllers that provide good power efficiency, have flexible voltage and switching frequency options, and integrate dimming capability with other features.

An example of a component that meets all these demands is the AL3069 from Diodes Incorporated. This is a boost controller and LED driver with four-channel integrated circuitry (IC) for LED backlighting applications. It is well suited for use in large TVs and display monitors.

The AL3069 has best-in-class channel-to-channel current matching of ±0.5% (typical), which ensures consistent screen brightness. Its boost controller input voltage operates over a wide range of 4.5V to 60V and can be used with standard 5V, 12V, 24V, and 48V supply rails.

The four sink channels have an 80V operating voltage. The current of the four channels is easily programmed from 20mA up to 250mA each (and 400mA pulse) by using an external resistor.

To improve dimming flexibility for applications that require fast response times, like gaming monitors, the AL3069 can support two independent dimming modes: direct pulse width modulation (PWM) dimming, and PWM to analog dimming. This versatility makes the device suitable for high-contrast LED backlight and high dynamic range (HDR) dimming applications.

The switching operating frequency of the AL3069 boost controller can be adjusted from 0.1MHz to 1MHz. This enables the use of low frequencies for higher efficiency, and high frequencies for smaller inductor form factors. It includes robust protection features such as cycle-by-cycle current limit, soft-start, open/short LED protection, and various features to protect against overvoltage and overtemperature.

[1] https://www.strategyr.com/market-report-led-backlight-display-driver-ics-forecasts-global-industry-analysts-inc.asp

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