"Born for efficiency", Nanxin launches the blockbuster wireless charging chip SC9621

The market demand for wireless charging products is currently being released continuously, but the industry technical specifications are still lacking. Therefore, on February 20, 2021, the Ministry of Industry and Information Technology issued a draft for comments on the "Interim Provisions on Radio Management of Wireless Charging (Power Transmission) Equipment", which stipulates that the rated transmission power of wireless charging equipment shall not exceed 50W. It can be foreseen that in the future, wireless charging of smartphones will no longer use charging power as the only criterion, and high-efficiency wireless charging and building a wireless charging ecosystem will be the new development direction of the industry.

SC9621 chip

Against this backdrop, Shanghai Nanxin Semiconductor has launched the high-efficiency/high-integration wireless charging RTX chip SC9621. The chip integrates the industry-leading low on-resistance power FETs, which can significantly reduce the temperature rise of the chip during high-power charging, thereby enhancing the experience and value of wireless charging for end customers. At the same time, the SC9621 chip has high-precision output current sampling within the full load range, which can help customers easily cope with rigorous foreign object detection (FOD) tests.

In the wireless charging system, there are three major systems: input power, transmission and reception. It is understood that the reason why SC9621 is called RTX (wireless charging receiving + transmitting chip) is that in addition to being a 50W wireless charging receiving chip, it can also be used as a wireless charging transmitting end by adding a power supply to the output end. At present, the SC9621 chip supports a maximum receiving power of 50W and a transmitting power of 15W. In the wireless charging system with a 50W output, Nanxin Semiconductor usually uses a USB power adapter that supports a maximum output of 20V.

In terms of performance, the outstanding advantage of the SC9621 chip is that it effectively reduces chip heating and improves power conversion efficiency. In the system composition of this chip, the current from the coil passes through a synchronous rectifier bridge composed of 4 MOSFETs, and the rectified voltage is filtered by the Vrect capacitor and output to Vout by the LDO, thereby outputting to the load. Among them, the LDO between Vrect and Vout can effectively block the ASK ripple. This is because the output voltage (range 3.5-20V) can be set through the digital interface, and the system automatically adjusts the Vrect voltage to keep the voltage difference on the LDO at an extremely low level.

In terms of power output, if a common 5W BPP transmitter board is used, the SC9621 EVM can quickly output 5V with a maximum current of 1 ampere. In applications with higher power output, Southchip Semiconductor increases the output voltage to save system losses. If used with the EPP15W transmitter, the SC9621 chip supports a maximum output of 12V 1.25A 15W; if used with the Southchip wireless charging transmitter, it can achieve a maximum power output of 20V 2.5A 50W.

SC9621 chip 5W power output display

SC9621 chip 50W power output display

In addition, in order to achieve higher charging efficiency, the SC9621 chip also supports direct charging and high-voltage direct charging technology. In direct charging applications, the charging system no longer uses traditional chargers to control the charging current, but uses the charging management chip to adjust the SC9621 output voltage to achieve the purpose of adjusting the charging current. Based on this, since there is no longer a buck or boost charger, the charging efficiency of the direct charging system will be greatly improved.

How does the SC9621 chip provide wireless power to other wireless charging receivers? Specifically, add 5V current to the Vout terminal of the SC9621 chip, write the TX (wireless charging transmitter chip) command through the GUI, and the SC9621 will enter the TX mode. At the same time, put another SC9621 on its coil as the RX (wireless charging receiver chip) to provide it with power for wireless transmission.

At present, with the increasing maturity of technology research and development and industrialization, wireless charging has transformed from a niche technology to an important charging solution for mid-to-high-end smartphones. According to data released by research firm Strategy Analytics, by the end of 2021, the number of smartphones with wireless charging functions will reach 1 billion. It is expected that this number will double to 2.2 billion by 2026. In this regard, Nanxin Semiconductor's launch of the SC9621 chip is not only a reflection of the pulse of the times, but also the implementation of the core development concept of "born for efficiency". At the same time, the chip will also bring high-performance, high-quality and high-cost wireless charging system solutions to the industry.