[Application Case] ​​48-channel output LED driver and interesting display board

When driving down a city street, look around and you will see more and more full-color LED signs and message boards appearing on the exterior walls of stores, restaurants and office buildings. With the rapid growth in the production of LED matrix display systems, advertising signs are now available at affordable prices for store owners. To support this demand, we are working hard to develop new technologies to further optimize the LED drivers that enable these displays.

Earlier this year, TI introduced the industry's first 48-output (48-channel) LED signage display driver product family. The TLC5954, TLC5955 and TLC5958 offer three levels of integration to support different degrees of flexibility.

So why do we need 48 outputs?

In the current LED signage market, 16-output drivers are used the most. At TI, the TI TLC5920 is an example. Therefore, a device with 48 outputs has three times the number of channels of a normal 16-output device, but the additional outputs will support red, green, and blue (RGB) LED lights in full-color signage applications.

In a typical LED display system design, a module contains 16 × 16 pixels and three 16-channel devices required for driving:

• IC1: 16 × 16, red

• IC2: 16 × 16, green

• IC3: 16 × 16, blue

When comparing the use of three 16-output devices versus one 48-output device, the clear advantage is the higher integration of the latter, which reduces the number of driver ICs on the PCB by a factor of 3. This simplifies the PCB layout.

以下是采用3个16输出驱动器的普通LED布局与采用1个48输出驱动器的相同布局的比较。在每张图的上半部分有256(=16×16)个RGB3合1LED灯，相当于768个独立LED灯。使用48通道驱动器可显著简化设计，无需线路跨接。

Three 16 - channel LED driver ICs

Single 48- channel LED driver IC

For example, we can look at a TI Design using the 48-channel TLC5958. In this example, there is a 64×64 pixel matrix design on a 4-layer board, which is 16 times larger than the above example, with a total of 12,288 LEDs.

As you consider these 48-channel drivers for your next design, here is some information to help you choose the ideal device for your system. In addition, you can watch the video "Industry's First 48-Channel LED Display Driver Family."

The TLC5954 LED driver is the simplest to use, integrating not only brightness control functions but also providing high flexibility through software. It does not integrate PWM generation logic, but contains a long shift register that can directly control the output stage switching. To drive the TLC5954, a powerful processor (FPGA, DSP and/or ASIC) is required to send switching data to the shift register. The advantage of the TLC5954 is that the software code can do anything you want with the processor. For example, you can implement complex and sophisticated spread spectrum PWM signal control to avoid or minimize EMI problems.

The TLC5955 LED driver is in the middle of these three devices in terms of integration and flexibility. The device integrates the industry-proven ES-PWM control, allowing the driver to be controlled by a lower power processor.

The third device in the 48-channel LED display driver family is the highly integrated TLC5958. It integrates 48Kb RAM and supports up to 32 times of time-division multiplexing control. This multiplexing technology reduces the number of driver ICs on the PCB. Without integrated RAM, it is difficult to achieve high-quality video output images because the time slot is too short. In addition, the TLC5958 also integrates pre-charge FET and low grayscale enhancement functions, which is particularly suitable for high-time-division multiplexing display systems.