How to choose the right LED driver solution for low voltage portable device backlight or flash applications?

White LEDs are widely used in small liquid crystal display (LCD) panels, keyboard backlights, 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, the inductive solution has the best overall performance; the charge pump solution uses a low-profile ceramic capacitor that occupies minimal board area and height; the linear solution is 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.

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 a high-performance LED driver in a 2.0 mm × 2.0 mm × 0.55 mm LLGA-12 lead-free package. It has an I2C interface and built-in progressive dimming function. It is specially designed to drive mobile phones and other portable devices. RGB LED decorative light and enhanced LCD backlight in the product. The NCP5623 achieves 94% peak performance and less than 1 microamp standby current, extending the battery life of the portable device to the longest. For typical applications, this component combines the advantages of a very small IC package with the ability to operate with only four passive components. The module 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 high-performance Quad-ModeTM fractional LED driver that drives up to four LEDs at 25 mA (see figure 1), the performance is as high as 92%. This four-mode driver is available in 1x, 1.33x, 1.5x, and 2x modes and is 10% more efficient than most charge-pump drivers in 1x, 1.5x, and 2x modes, and requires no additional capacitance. 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 capacitors), and reduce noise, providing a simple solution for entry-level portable products and the low-cost handset market.

LED driver solution specifically for camera flash

It is worth mentioning that in camera flash applications, in addition to the NCP5005 and CAT4134 inductor boost drivers, you can also use the charge pump driver NCP5680 and CAT3224 to support high megapixel camera flash, and replace Xenon flash, with slim design. Among them, NCP5680 and CAT3224 are supercapacitor-based LED drivers that provide large flash currents of 10 A and 4 A, respectively.

In fact, today's 5 million pixels or higher resolution cameras require high-brightness flashes in order to take high-resolution photos in low light. Today's white LEDs can provide this level of light energy, but need to be nearly 400% more energy than the camera battery can provide. Taking ON Semiconductor's NCP5680 as an example, this component works with a battery to manage a supercapacitor to drive the LED flash to full brightness, providing a large peak current of up to 10 A. The integrated driver in the NCP5680 also manages supercapacitors to handle other peak power functions such as zoom, autofocus, audio, video, wireless transmission, GPS data reading and radio frequency (RF) amplification to extend battery life without giving up slim design . The NCP5680 integrates all the circuitry needed for supercapacitor charging, inrush current management, and LED current control, saving designers time, board space, and component cost.

The CAT3224 is the industry's first 4 A single-chip supercapacitor LED driver (see Figure 3). It integrates a dual-mode 1x/2x charge pump and provides three key functions: precision supercapacitor charge control, current discharge to LED flash management And provide constant current for the LED flashlight mode. The operating currents of these three modes can be easily set with three external resistors, and can absorb up to 4 A of LED flash pulse current. The high peak current advantage of supercapacitor technology, combined with the simple parallel logic interface of the CAT3224, makes this component an excellent choice for LED replacement for xenon applications.

Other novel LED drivers/controllers

In addition to the above LED drivers, ON Semiconductor offers other innovative products such as the NCP5890 and CAT3661 for low voltage portable device applications. Among them, the NCP5890 is a unique lighting management integrated circuit (LMIC) that integrates liquid crystal display (LCD) backlighting, decorative light control and ambient light sensing in a very small package of 3 mm x 3 mm x 0.5 mm.

As we all know, today's portable electronic products are popular with larger LCD screens and LED lighting effects. To meet all of these lighting requirements, hardware designers often need to use several LED drivers. Due to the limited board space, a large amount of software programming and microcontroller (MCU) resources are typically required to achieve more advanced lighting effects. ON Semiconductor offers the NCP5890, a simpler single-chip silicon solution with a variety of command-controlled lighting effects to help hardware design engineers meet their specific lighting and power design goals. The lighting management IC features a 30 V output voltage capability that drives a serial LED for balanced backlighting of the LCD screen. In addition, this component controls three sets of white LEDs or RGB LEDs to create a decorative light pattern on the keyboard or chassis that forms a unique combination with the backlight. The driver also adjusts the backlight current based on the brightness of the ambient light to extend battery life. The NCP5890 is a dedicated solution for applications such as compact smartphones.

Today, more and more innovative portable devices are powered by coin cells, such as blood glucose meters, digital thermometers, oximeters, respiratory analyzers, and physiological monitors in medical applications. Due to the unique features of this battery and the long working life required, these compact applications require custom LED drivers that not only manage the backlight but also monitor battery power. In such applications, the CAT3661 2 to 2.5 V single LED driver that ON Semiconductor plans to introduce in the second half of 2010 is available. This component also features ON Semiconductor's patented Quad Mode charge pump architecture with up to 92% efficiency and quiescent current as low as 150 μA, providing adjustable low battery detection and robust LED fault monitoring, soft Protection features such as start-up and short-circuit limiting, in a low-profile 3 x 3 mm TQFN-16 package, are ideal for these portable device applications.

summary:

As the premier supplier of high-performance, high-performance silicon solutions for green electronics, ON Semiconductor offers comprehensive LED driver or control solutions using its low-voltage and high-voltage technologies and expertise in power management solutions. Program. This article highlights various white or RGB LED drivers from ON Semiconductor that use different topologies for backlighting or indicator applications in low-voltage portable devices, and specifically describes ON Semiconductor's portability for high current capability. Drivers for flash applications, as well as integrated lighting management ICs and LED drivers optimized for button cells, make it easy for engineers to choose the right product for their application.

Reference data:

1. ON Semiconductor LED Lighting Solution Selection Manual,
2. NCP5680 data sheet,
3. CAT3224 data sheet,