Vehicle-Mounted OLED Display Module ESD/EOS Protection Solution

The eDP communication protocol stipulates that data transmission is mainly divided into three parts: high-speed link (Main Link), secondary channel (AUX), and hot plug (HPD) for video transmission. High-speed link (Main Link) can support 1~4 pairs of differential signal communication, which is the main transmission channel of data. Currently, the most common version of eDP communication protocol is V1.4, and the maximum transmission rate of single link is 5.4Gbps. The latest eDP 1.5 protocol single link also supports the maximum transmission rate to 8.1Gbps. In addition, the auxiliary channel (AUX) has a low transmission rate and can perform functions such as device communication detection and device control signal communication. 

In order to ensure the display stability of OLED modules, manufacturers usually conduct ESD simulation tests on their manufactured display modules. In commercial display modules, only 8kV contact discharge and 15kV air discharge are generally required to be tested. Due to the strict requirements of the vehicle-mounted system, the highest ESD test level will be elevated to 15kV contact and air discharge. The test results determine that most of them are upgraded from Class B to Class A, that is, the panel flash self-recovery phenomenon is not allowed during the test. Under such strict test conditions, the TVS protection solution for modules needs to be watertight. Of course, in the design of the TVS protection solution of the OLED module, it is not only necessary to protect the lines of the eDP interface, but also to protect the touch SPI signals and various power signals to ensure that ICs at all levels are not affected by the ESD test and pass the ESD simulation test smoothly. 

In the protection of the eDP interface, due to the high transmission rate of the high-speed link (Main Link), the capacitor value should not be too large when selecting TVS. At the same time, the high-speed signal is susceptible to ESD interference. It is necessary to choose a TVS product with a smaller clamping voltage parameter, which is better to protect the signal. Since the central control flat panel display module is a vehicle-mounted front component, manufacturers often require TVS to pass the AEC-Q101 vehicle certification when selecting components. For eDP high-speed links (Main Link), it is recommended to use low-capacitance four-channel AZ9143-04F or eight-channel AZ9143-08F as ESD and EOS protection design. The multi-channel DFN package has a simple layout and does not require drilling and wiring, which can reduce EMI and improve the protection effect. Auxiliary Communication (AUX) uses dual-channel AZ9515-02F as ESD and EOS protection design, which is the best cost-effective product for low-speed line protection. In addition, the SPI communication line of the touch IC can also use the four-channel AZ9143-04F or the two-channel AZ9515-02F as ESD and EOS protection.

Table 1. Basic parameters of signal line protection TVS

If the protection design of OLED display module is not perfect, the phenomenon of black screen and restart will often occur during the test. In addition to the interference of ESD or EOS to the signal line, the interference of various chip power supplies and driving power is also one of the reasons. For the power supply circuit, not only should we pay attention to the protection of ESD, but also the protection of EOS, because they often bring serious damage to various chips and other devices of the display module, and even increases the customer return rate. The vehicle-mounted OLED display module has many power lines, and the PCB area is often small, therefore, the TVS protection device used is mainly 0402 or 0603. Choosing TVS products with higher IPP current and lower clamping voltage will have more obvious protection effect on EOS and the stronger the ESD and EOS immunity of the entire OLED display module. 

There are many power lines that need to be protected in the OLED module, such as PMIC VDD 1.8V low-voltage power supply. Amazing Microelectronic Corp. recommends AZ9625-01F with ultra-low operating voltage and clamping voltage, which has excellent protection effect. In addition, there are VDD_3.3V, AVDD, DVDD, VGH/VGL, VIN and other different voltage lines that need to be protected. It is recommended to use TVS products with the same working voltage.

A sound ESD and EOS protection design can ensure that the performance of the product is not affected, and it is also an important method to reduce customer returns. With various product choices and rich design experience, Amazing Microelectronic Corp. provides more comprehensive ESD and EOS protection solutions for terminal product designs.