Choose the right LED driver solution for low voltage backlight or flash applications

White LEDs are widely used in small liquid crystal display (LCD) panels and keyboard backlighting and indicator applications. High-brightness LEDs are used in flash sources for cell phones and digital cameras. These applications require an optimized driver solution that extends battery life and reduces printed circuit board (PCB) area and height. In these applications, common LED driver solutions involve different topologies of linear, inductive or charge pump types, each with its own characteristics. For example, inductive solutions have the best overall energy efficiency; charge pump solutions use low-level ceramic capacitors, occupying minimal board area and height; linear solutions are ideal for color indicators and simple backlighting applications. ON Semiconductor offers LED driver solutions for all three types of topologies (see Figure 1) to meet different application needs.

Figure 1: Example of different LED driver topologies for low-voltage portable device applications

In terms of charge pump type solutions, ON Semiconductor offers products that support different dimming types, such as single mode, dual mode, triple mode or quad mode charge pump solutions, such as CAT3200, NCP5602, NCP5612, NCP5623, CAT3606, CAT3616, CAT3626. , CAT3603, CAT3604, CAT3614, NCP5603, etc. Take the NCP5623 as an example. This is an energy-efficient LED driver in a 2.0 mm × 2.0 mm × 0.55 mm LLGA-12 lead-free package with an I2C interface and built-in progressive dimming. It is specifically designed to drive portable products such as mobile phones. RGB LED decorative light and enhanced LCD backlight. The NCP5623 achieves 94% peak energy efficiency and less than 1 microampere standby current, extending battery life in portable devices to the longest. For typical applications, the device combines the advantages of a very small IC package with the ability to operate with only four passive components. The device also features short-circuit and over-voltage protection to protect the system from LED failure.

It is worth mentioning that ON Semiconductor also offers a variety of four-mode charge pump LED drivers, such as CAT3636, CAT3637, CAT3604V, CAT3643, CAT3644, CAT3647, CAT3648 and NCP5604A/B. Take the CAT3648 as an example. This is a patented, energy-efficient, quad-mode adaptive fractional LED driver that drives up to four LEDs at 25 mA (see Figure 1). ), energy efficiency is as high as 92%. This four-mode driver is available in 1x, 1.33x, 1.5x, and 2x modes and is 10% more energy efficient than most charge pump drivers in 1x, 1.5x, and 2x modes, and requires no additional capacitors. Take LED driver performance to the next level. These drivers are suitable for driving white LEDs in low-voltage portable devices with small-size LCD backlights and LED flash applications.

In terms of inductive boosting solutions, ON Semiconductor offers different products using PWM dimming, such as CAT32, CAT37, CAT4137, CAT4139, CAT4237, CAT4238 and NCP5005, NCP5010 with output currents between 20 mA and 50 mA, and CAT4240 (250 mA), NCP5050 (600 mA) and NCP1422 (800 mA) provide greater output current. These inductive boost drivers are suitable for driving white LEDs in low voltage portable device backlighting and flash applications.

In terms of linear backlight driver solutions, ON Semiconductor offers a variety of single-mode LED drivers for two to four channels, such as CAT4002A, CAT4002B, CAT4003B, CAT4004A, and CAT4004B. These backlight drivers offer 32 levels of dimming control with 25 mA fixed or adjustable output current and very low shutdown current of less than 1 μA with no switching power supply noise issues. These single-mode LED drivers are often used as part of a system-level approach to designing backlight circuits that integrate low-voltage LEDs with simple LED drivers. These driver circuits are simple, helping to extend battery life, reduce costs (such as saving external capacitance), and reduce noise, providing a simple solution for entry-level portable products and the low-cost handset market.

Figure 2: CAT4002B application circuit diagram

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