Introduction to the full-link solution for mobile phone fast charging and a brief analysis of chip companies

Mobile phone fast charging has developed rapidly in recent years, especially the five major domestic mobile phone brands, which have surpassed Apple and Samsung in charging power and speed, and led the fast charging chip manufacturers to continuously iterate and innovate in technology and products.

Texas Instruments, an international giant in analog chips, has always been an oligopoly in the power management market and a benchmark for imitation in the industry. It also has a full layout in the mobile phone fast charging market. However, in recent years, with the substantial improvement in the technical capabilities and R&D of domestic charging chip manufacturers, and under the influence of the international environment and the support of national policies, it has achieved considerable development. Some emerging domestic semiconductor companies such as Nanxin and Xidiwei have performed very well in the mobile phone fast charging market.

Fast charging has become a must-have feature for mid- to high-end mobile phones, and it also accounts for a large part of the cost of mobile phones. This is a system engineering project with a long link, including charging heads, interfaces, charging cables, fast charging chips, battery connectors, battery cells and other power paths, as well as the communication protocol known as the soul of fast charging. Each part of the power link must be efficient and high-power to make fast charging possible, and there cannot be any shortcomings.

This article introduces the full-link chip functional modules of mobile phone fast charging solutions, including charging heads, mobile phone fast charging chips, protocol solutions, etc.

charger

The charging head is the energy provider of the entire fast charging link. It has developed rapidly from the earliest 2.5W to the current highest 200W. And with the support of the latest Gan material, the efficiency can be made higher and the volume can be made smaller.

The following figure is a block diagram of an AC/DC solution, which is mainly composed of three control modules: primary side, secondary side, and protocol, as well as transformers, isolated feedback devices, etc. According to different power levels, corresponding selection is carried out to meet different power requirements and customer needs.

Most AC/DCs use the classic flyback architecture. Under high power conditions, soft switching, gallium nitride devices, and PFC technologies are more often used to further improve efficiency and thereby increase power.

Some of the miniaturized lipstick chargers and biscuit chargers we have seen use a large number of new materials and technologies such as gallium nitride MOS and planar transformers.

In the charging head market, foreign and Taiwanese brands were the main ones before. Foreign brands mainly made primary and secondary sides, such as ON, PI, Dialog (iwatt), and Infineon (Cypress) that focused on protocols; Taiwanese brands mainly made primary and secondary sides, such as Tongjia and Onbao, and Richtek that could provide complete solutions.

In recent years, local domestic manufacturers have made rapid breakthroughs in AC/DC, such as Silergy, Jewatt, Xinpengwei, Silan Microelectronics, etc., which focus on primary and secondary sides; Ingenic, Zhirong, Huinengtai, etc., which focus on protocols; and Shanghai Nanxin, which provides complete solutions. It is worth mentioning that Nanxin also has a complete direct drive solution for the third-generation gallium nitride.

Fast charging chip in mobile phone

The fast charging solution in the mobile phone is the most core link in the entire charging chain. Its main function is to efficiently convert the energy sent from the charging head and charge it in a way that the battery can accept, and also complete a series of detection and protection functions.

Efficiency has always been the biggest bottleneck restricting mobile phone fast charging. Because the mobile phone space is very small and the user experience must be considered, heating is a very troublesome problem.

The charging architecture in mobile phones has gone through three generations of development so far:

Linear charging

Switch charging

Charge pump charging

Linear charging has been completely phased out on smartphones, with only ultra-low-end feature phones still using it.

Switching charging is the mainstream of mobile phones at present, with an efficiency generally between 88% and 92%, and a charging power level of about 18W. For example, TI's BQ2560x is a universal main charger that can complete the complete charging process of pre-charger, maximum 18W constant current stage, and end charger.

In a mobile phone, the main charger is usually integrated into the platform's PMI. Some manufacturers will add an external switch charging chip to disperse heat and achieve a better user experience.

Some special solutions can achieve higher efficiency, such as MPS's MP2762, TI's BQ25790, and Nanxin's SC8982, which is a buck-boost charging solution for dual-string batteries and can achieve a maximum efficiency of about 95%.

Switch charging belongs to the second-generation charging solution, but it still has very strong technical difficulty. There are not many domestic manufacturers that can do it well. At present, mobile phone platforms and TI are the absolute main force. Domestic manufacturers are mainly Silergy, Shengbang Micro, and Nanxin.

Charge pump charging is the only solution for fast charging of mid-to-high-end mobile phones. It has super high efficiency, generally around 97%, and is an auxiliary charging solution for the constant current charging process.

The scientific name of the charge pump is "high-voltage direct charging". When talking about direct charging, we have to mention the pioneer in the domestic power supply field, OPPO's "low-voltage direct charging" technology. "High-voltage direct charging" is developed from this technology.

Charge pumps generally work according to voltage ratios, such as the classic 2:1, high-power 4:2, 4:1, and ultra-high voltage 6:2.

The 2:1 products are mainly used in medium charging power levels of 30-50w; 4:2 is mainly used in high-power dual-string battery solutions; and the latest 4:1 architecture is used in high-power 1S battery architecture, which also benefits from the rapid development of battery cell charging rates.

After ON, Dialog, and TI first launched charge pump products, domestic mobile phone manufacturers immediately sensed a huge change. At the same time, many domestic chip manufacturers were also actively following up, and even achieved a certain degree of transcendence in a short period of time.

The first mass-produced charge pump of a domestic semiconductor was a 4:2 charge pump chip from Hi-Micro, which was used for simple voltage conversion; but the first manufacturer to mass-produce a charge pump charger chip was Shanghai Nanxin's SC8551, which is compatible with the industry's classic BQ25970.

In addition to the platform, several manufacturers have launched a variety of charge pump products, such as foreign brands:

TI: 2:1, 4:2 charger

Lion: 2:1 charger; 4:2 converter; 6:2 converter (just acquired by Cirrus Logic)

Maxim: 2:1 converter

Domestic brands include:

· Nanxin: 2:1 charger (30w/40w); 2:1 charger with protocol; 2:1 converter; 4:2 converter; 4:2 charger; 4:1 charger; 6:2 converter;

· Hi-Micro: 2:1 charger; 4:2 converter

· Silergy: 2:1 charger; 4:2 Charger

· Xinmai: 2:1 charger; (formerly Silicon Mitus, acquired by state-owned capital this year)

· St. Bonnie: 2:1 charger;

Charge pump chargers directly provide high-power charging to batteries, so safety requirements are very high. Branded mobile phone manufacturers are very cautious in introducing them. Currently, apart from platforms and TI, only Nanxin's products have been shipped in large quantities among domestic manufacturers. In some recent disassembly reports, it can be seen that many of Nanxin's new charge pump products are used in mobile phones of multiple brands. Due to the particularity of this product, the leading manufacturers will continue to be strong, and the chances of latecomers are not great.

The figure below is a block diagram of the fast charging solution in the mobile phone, which also includes the charging protocol chip solution.

Charging protocol

The protocol is the soul of fast charging. During the entire fast charging process, the mobile phone system and the charging head must communicate in real time, accurately adjust the voltage/current and monitor in real time to achieve the fast charging process of the charge pump.

At present, all major mobile phone brands have their own private protocols, such as:

Xiaomi's private protocol based on CC;

Huawei/Honor’s SCP;

OPPO's VOOC;

VIVO's Flash charger;

Transsion’s I2C private protocol, etc.

Mobile platforms also have their own protocol solutions, such as:

Qualcomm's QC series

MTK's PE

Of course, there are also specialized protocol alliances, such as:

PD of USB-IF in the United States;

· UFCS of the domestic green alliance.

Most of the protocol chips in mobile phones are implemented through platforms or MCUs. There are also some special occasions that require customization, such as Ingenichide, Weltrend's QC protocol chips, Richtek's PD phy, etc.

In the future, China's own interoperability protocol, UFCS, is widely expected to be supported by all major manufacturers. In addition to the above manufacturers, Silergy, Nanxin, Rockchip, Onbao, and Xinpengwei are also in the alliance, actively participating in the formulation of the UFCS protocol and the development of chips. From the long-term trend, various protocols will inevitably be unified and integrated into the platform.

The protocol chip needs to be present in both the mobile phone and the charging head. Please refer to the block diagram in the previous chapter for the protocol chip inside the mobile phone. The following is the basic application diagram of the protocol chip in the charging head.

Interfaces and cables

Not only do the chip modules in the charging link need to be upgraded based on the demand for fast charging, but the interfaces and cables also need special treatment to reduce impedance and heat.