Indoor p1.25,P1.0,P0.9,P0.8,P0.7 mini-LED and micro-LED fine pitch LED display modules using IC MBI5864,MBI5359 Usage

      Indoor p1.25,P1.0,P0.9,P0.8,P0.7 mini-LED and micro-LEDfine pitch LED display modules using IC MBI5864,MBI5359 Usage

Foreword

Thanks to the advancements in display technology and improvements of resulting imaging, the demand for mini-LED and micro-LED continues to grow. Display makers are aggressively vying for the sub-P0.9mm narrow pixel pitch (NPP) market. Nevertheless, super-fine-pitch LED display modules mean less space for driver ICs and their ancillary components if the number of load pixels remains the same, which will be very challenging for module designers. Therefore meeting the demand for fine-pitch displays with higher-pitch offerings is a given. Reduced power consumption with high-scan products needs to be addressed too. This article examines the design of super-fine-pitch LED display modules with pitch smaller than P0.9mm. Figure 1 shows the relationship between available PCB space vs. LED driver ICs of varying scans for fine-pitch LED displays.

No. of scans vs. pitches for fine-pitch LED display module

Design consideration for

super-fine-pitch LED display module 1 – Total number of chips used and their space allocation

The first and foremost consideration in designing super-fine-pitch LED display modules is the shrinking space for driver ICs and their ancillary components if the number of load pixels remains the same. As a typical module won't be bigger than 300mm x 300mm, the smaller the pitch, the more driver ICs are required to drive more LEDs. In other words, driver ICs will account for a bigger piece of the PCB space pie. For example, a 100mm x 100mm LED module with 48-channel driver ICs and sub-P1.2 display will need over 18 driver ICs for sub-32-scan applications. Figure 2 shows the relationship between the number of driver ICs and pitches/scans. The chart clearly indicates 64-scan applications effectively reduce the total number of driver ICs needed. Figure 3 shows how much space 64-scan and 32-scan ICs need. With a P0.7 applications, 32-scan chips will take up 32% of the space. The PCB will run out of space with the chips and ancillary circuitry and components. In other words, 64- scan driver ICs have an absolute edge in fine-pitch applications.

Total number of drive ICs used

(Based on 100mm x 100mm module with 48-channel LED driver chip) Figure 

2Differences in no. of chips in typical applications. Significantly fewer 64-scan driver chips are needed.

Percentage of PCB space IC takes up (e.g. 8mm x 8mm BGA package)

Figure 3 Percentage of space needed.

64-scan chips take up significantly less space.

64-scan drivers can drive more LEDs while taking up less space. However, the chip will have more pinouts. Figure 4 shows a potential scenario of putting high- and low-scan driver chips in the same package. Bad pinout design and choosing the wrong number of PCB layers will make trace design more difficult. It may take even longer to design the board. As the number of scans increases, every channel will see peak current rise proportionally. Given the white balance ratio, current running through the red LED will double that of green and blue LEDs. Therefore when we design the PCB for high-density, fine-pitch applications, we must carefully choose the trace width to take into account the current as well as the corresponding EMI. In general, 1mm-wide trace is required to pass 1A current with 1oz. copper. Macroblock is very experienced and has the expertise in chip pinout. We also follow the reference board as the chips are produced to minimize resource waste and effectively shorten time to market, which in turn lowers design barriers and improves project efficiency.

Design consideration for

super-fine-pitch LED display modules design consideration 2 – Faster data rate

As 64-scan driver ICs need to manage more scans, the chips need more data. As Figure 5 shows, data rate needs to go up to maintain the same refresh rate. However, higher data rate means more high-frequency EMI and shorter scan time. To address high-frequency EMI, we need additional EMI solutions or cases with heavier shield. Shortening scan time will compress the existing fading time and over-optimized gradation time, reducing their positive effects including ghosting removal and dim line at the first scan line. Moreover, there may not be enough time for the channels to fully open while displaying low-grayscale information, which can hurt brightness. Resulting process shift may have different darkening effects depending on scans, even causing display anomaly and low-grayscale red stripes. These data-processing issues need to be taken into account while designing super-fine-pitch LED display modules. To cover all bases, Macroblock always works with partners to jointly create rules for developing controllers.

This is a simplified presentation of the amount of data =

no. of channels per square x no. of cascaded chips x grayscale bit depth.

Figure 5 Increasing the no. of scans needs increased data rate (32-scan at the top, 64-scan at the bottom.)

Figure 6 Slow data rate may cause non-uniformity at low-grayscale

Design consideration for

super-fine-pitch LED display modules 3 – stencil and mounting techniques

Pitch is getting increasingly small with super-fine-pitch LED display module applications. The LED industry is going mini-LED, micro-LED and even COB, which challenges existing stencil and mounting techniques. For example, as component density increases with super-fine-pitch applications, PCB traces are getting thinner. Load current becomes an issue. Moreover, to ensure yield with available processes, traces need to be wider than 5mil and vias bigger than 8mil, furthermore complicating the design of super-fine-pitch LED display modules. Therefore to develop super-fine-pitch LED display modules, breakthrough in stencil technology is essential. On the other hand, existing mounting techniques put a 0.5mm limit on the distance. Though 64-scan driver ICs can minimize external components, the 0.5mm limit will make design more difficult sooner or later as pitch shrinks further. Figure 7 shows it is very difficult to keep the 0.5mm criterion with the tiny available space for LED module (100mm x 60mm). Nevertheless, 64-scan driver ICs can simplify the entire layout.

Figure 7 Limited space for LED modules (100mm x 60mm). Components and circuitry are close and complex.

Braving the challenges

To optimize LED module production cost, it is essential to introduce leading technology in an effort to improve the products' competitive advantage, lower the total cost and maintain the quality at the same time. Given the mounting cost and the design complexity of modular components, 64-scan LED driver ICs can significantly reduce the number of LED driver ICs needed and lower mounting cost and simplify layout, which improve manufacturing efficiency. Figure 8 proves that with available space of 100mm x 60mm, we need a 48-channel, 64-scan LED driver chip (MBI5864) to drive the fine-pitch LED module (P 0.6). Figure 9 shows 32-scan IC (MBI5359) can simplify circuit layout with a board of 0.75 dot pitch.

Figure 8 Layout of a 0.6 LED module with 48-channel 64-scan driver IC (MBI5864)

Figure 9 Layout of a 0.75 LED module with 48-channel 32-scan driver IC (MBI5359)

To address the design challenges posed by super-fine-pitch LED display modules, Macroblock developed MBI5864, a highly-integrated LED driver IC supporting 64 scans and dual-edge trigger.

Macroblock coined the phrase "New Basics" for the best available LED driver ICs and ancillary components. Super-fine-pitch LED display combined with New Basics will easily maximize cost effectiveness without you worrying about data rate and picture quality.

Conclusion

As displays go indoor and the challenges of high-quality images emerge, developing fine-pitch LED display module is inevitable. Though technical challenges continue to arise, Macroblock is so experienced in the area that we have researched and developed LED display module offerings that meet the demand of LED display market for the latest and the most premium solutions.

Want to know more about how 64-scan LED drivers affect super-fine-pitch LED display modules? Visit our websit<a href="http://www.mblock.com.tw/" \h"="">e www.mblock.com.tw for details.