Application of LCD driver circuit in smart grid system

　　Universal liquid crystal drivers can be used in early electronic metering meters. With the development of my country's smart grid, new application requirements have been put forward for liquid crystal drive circuits.

　　The common LCD driver circuits are mainly Philips' PCF8566 and PCF8576. Taking PCF8576 as an example, this circuit can meet more display driver requirements because of its cascading function, and can be used as a display driver chip in electronic metering meters.

　　The general display driver circuit can meet the requirements of the general segment display LCD driver, and this display method is relatively simple. However, for industrial-level applications such as smart grids, many indicators need to be strengthened, mainly including: 1. The ESD level of the whole machine is required to reach 15KV; 2. The power-on mode and various output requirements are high; 3. In line with green environmental protection requirements, the lower the circuit power consumption, the better.

　　In addition, the technical requirements for the smart grid State Grid single-phase meter are that the number of LCD display segments should be around 136. The original Philips PCF8566 display segment number is too small (96 segments), while the PCF8576 display segment number is too large (160 segments), and the cost is high.

　　In response to the technical requirements of the State Grid single-phase meter, we have specially developed a universal display driver chip BL55070 that meets the needs of the State Grid single-phase meter. This chip is a product with all independent intellectual property rights. It not only fully meets the industrial-grade requirements of the smart grid, but also has better EMC and main technical indicators than similar foreign products. This chip has specially added a SLEEP mode function. In this mode, the power consumption is much lower than similar foreign products, meeting the requirements of green environmental protection. It has 140 display segments, and the functional design is compact. It uses LQFP44 packaging to achieve the best cost-effectiveness. Based on the chip circuit, Shanghai Belling has realized the research and development and industrialization of the driver series product circuit to fully meet the diversified needs of customers. The specific technical indicators of the circuit are as follows: monolithic integrated LCD controller/driver; selectable back-drive mode: static or 2, 3, 4 composite; selectable display bias voltage: static, 1/2 or 1/3; wide operating voltage range 2.5~5.5V; two-wire serial bus interface; 35×4 display data memory; low power design, 5V dynamic operating current is 14µA in power saving mode, 9µA at 3.3V, and the operating current is about 1.5µA when the SLEEP mode is set by instruction; universal flashing mode; high anti-EMC performance; LQFP44 package.

　　There are three main aspects of our technological application innovation in the development of display driver circuits. The first is low-power design. According to the requirements of the meter field, all MOS tubes inside the circuit are designed with low power consumption in mind, so the power consumption of the product is 30% lower than that of similar foreign products. At the same time, through low-power design and sleep commands, the power supply current is further reduced to about 1.5µA. Second, strong EMC capability. According to the application requirements of the circuit, we use special ESD design and integrated circuit layout schemes to enable the device to meet the smart grid customers' requirements for the whole machine ESD of 15KV, and the actual ESD capability reaches 20KV. Third, it can meet special display requirements. Smart meters have high requirements for power-on mode and various outputs. Without affecting other parameters, we redesigned the line module to ensure customer application.

　　Since the typical application circuit of BL55070 is designed for the requirements of smart grid state grid single-phase meter, it has simple periphery, compact functions and high cost performance. It has been widely adopted by many meter manufacturers in the state grid single-phase meter system and achieved good economic benefits.