Editor’s Note: This article is from the WeChat public account “Semiconductor Industry Watch” (ID: icbank), author Fan Chen, 36 氪 authorized to release.It is said that the new iPhone in 2019 will finally abandon the ancestral Wufu Yi’an (5V/1A) charging head.After all, if you use the standard “five blessings” to charge your iPhoneXs Max, it takes 210 minutes to fully charge.The best scores of other children’s Android are generally within an hour.Of course, the performance of other children’s children is not improved in one day. Since the launch of QC Quick Charge in Qualcomm in 2013, the development of Android fast charging technology has embarked on a fast lane, and various technologies and standards emerge one after another.Charging time keeps refreshing the limit.Before we can find out the fast charge, we must first know how the battery is charged.Lithium battery charging generally takes three stages: pre-charging, constant-current charging and constant-voltage charging.In the pre-charging stage, the battery voltage is low, the activity is poor, the internal resistance is large, and only a small charging current can be accepted; as the battery voltage rises, the battery activity becomes stronger, the internal resistance becomes smaller, and a larger charging current can be accepted (70% of the battery capacity is basically charged in the constant current phase); when the battery voltage rises to the vicinity of the cutoff voltage, the system voltage no longer rises, and the charging current is automatically reduced until the battery is full.The mobile phone uses the detected battery voltage to display the remaining power. For example, when the battery voltage is 4.4V, the power is 100%, and when the voltage is 3.6V, the power is 0%, and the mobile phone automatically shuts down.How to achieve fast charge?Charging time = battery capacity / charging current * coefficient, the most direct way to shorten the charging time is to increase the constant current charging current.To increase the current, the output power of the charging head (the input power of the mobile phone) is increased.Therefore, in recent years, the output power of mobile phone charging heads has been upgraded from 5W, 10W, and 18W. VIVO has released 120W fast charging technology in 9012.So how to improve the output power of the charging head?Power P = U * I, increase power or increase the voltage, or increase the current, or both.The industry has evolved three programs of high-voltage fast charging, low-voltage fast charging, and charge pump fast charging.1. High-voltage fast charge In 2013, Qualcomm released QC1.0, and the charging power rate was first increased to 9W (5V/1.8A). In the next year, the advanced version of QC2.0 was introduced to further increase the charging power to 18W (9V/2A or 12V/).1.5A), from then on, established its position as a leader in the field of high voltage fast charging.Qualcomm chose a high-voltage fast charge program for a reason.Around 2014, the mainstream charging interface for Android phones was MicroB, and the maximum charging current supported by MicroB was 2A.As a third-party supplier, Qualcomm will continue to increase the charging power based on the MicroB interface, only to increase the charging voltage.In addition, the high-voltage fast charging solution is relatively easy to implement, and the cost increase is not obvious. It is not necessary to replace the interface and the charging line, and the terminal customer is more acceptable, which is consistent with Qualcomm’s positioning as a “platform”.But the high-voltage fast charge program has a serious problem – fever.When the 9V/12V voltage output from the charging head enters the mobile phone, it will be secondarily stepped down by the charging IC in the mobile phone.In the process of reducing the voltage and increasing the current, the conversion efficiency of the traditional BUCK type charging IC is only 89%, and the energy loss will bring about severe heat generation (18W fast charging will only have 1.96W heat loss on the charging IC), andThis phenomenon will become more serious as the charging power is further increased.2. Low-voltage fast charge “charge for five minutes, talk for two hours”, in 2014 OPPO launched VOOC flash charge 22.5W (5V/4.5A) low-voltage fast charge technology.Since the low-voltage fast charge directly increases the charging current, there is no need to perform secondary conversion of the voltage, so the problem of high-voltage fast charge and heat generation is well solved, and it is also possible to “play while playing”.In order to solve the problem that the MicroB interface can not accept large current and the parasitic resistance of the traditional wire is too large, OPPO has specially customized the charging interface, charging cable and charging head for VOOC flash charging.As a mobile phone manufacturer, OPPO is free to define the configuration of its own mobile phone without regard to compatibility issues.This is also the main reason why OPPO is different from Qualcomm and launched a low-voltage fast charging solution.Although the low-voltage fast charge solves the heating problem caused by the high-voltage fast charge and the second step-down, the low-voltage fast charge also faces many challenges in the continuous improvement of the charging power. The increasing current flows through various components.It is a test, the heat loss of the wire and the interface will become larger, the power consumption of the whole system will be multiplied, and the corresponding customization cost is also higher.Continue to increase the charging power, high voltage and high current seem to be necessary, and the common enemy of high voltage and high current is heat, one of the main reasons for heat is the heat loss of the charging IC, TI has done calculations,At the same heat loss, the efficiency increases by 2.5% and the charging current can be increased by 27%.Therefore, improving the efficiency of charging ICs has become the key to the further development of fast charging.3. Charge Pump The fast charge pump is a non-inductive DC-DC converter that uses a capacitor as an energy storage element for voltage conversion, which can halve the voltage while doubling the current.And its conversion efficiency can reach about 97%, much higher than 89% of ordinary charging IC.This makes the charge loss of the charge pump at 60W charge lower than that of the ordinary charge IC 18W. Such low heat solves the bottleneck of high-voltage fast charge, making ultra-high power fast charge possible.In addition, the standard Type-C interface supports 3A current, while the USB PD protocol can support up to 100W charging power (20V/5A). The large-scale popularity of the Type-C interface also improves the charge pump fast charge compatibility.Sex.Based on the charge pump technology, Meizu released the Super mCharge 55W fast-charge concept machine in 2017. MW immediately launched the BQ25970 production version of the charge pump.Huawei, which originally planned to use 5V/8A on 40W fast charge, decisively switched to 10V/4A charge pump solution in 2018 and applied it on Mate20pro.(And Meizu has not yet produced 55W fast charge for various reasons, its latest flagship 16s pro is only equipped with 24W fast charge.) Of course, the charge pump is not omnipotent, it needs to cooperate with the conventional charging IC and the protocol control IC in the charging head.Charge the phone together.Since the charge pump generally does not have the function of voltage regulation of the BUCK type charging IC, the precharge and the final constant voltage charging phase are still completed by the conventional charging IC.In the initial stage of constant current charging and constant voltage charging, the mobile terminal needs to negotiate the charging head through the USB PD protocol (or proprietary protocol) to output a suitable voltage and charge pump for constant current and constant voltage charging.When the charging head voltage is adjusted to twice the battery voltage, the charge pump can normally perform constant current and constant voltage charging.The 40W charge pump fast charge is roughly charged as shown in the figure below.In February 2019, VIVO sub-brand IQOO introduced an advanced version of the 44W charge pump fast charge, which can be filled with 4000mAh battery in 46 minutes.To further improve the efficiency of the charge pump at high currents, IQOO uses two BQ25970 parallel shunts to improve efficiency while reducing body heat.(In fact, the maximum power of IQOO and Mate20pro charging is about 36W, but the maximum power charging time of IQOO is longer than that of Mate20pro, and all the required time is shorter. IQOO’s nominal 44W is more to indicate that it is compared with friends.The charging efficiency is higher.) The core of fast charging – the core of fast charging chip fast charging solution is fast charging chip. Take NXP’s charge pump fast charging solution as an example. The core chip generally includes two types of mobile phone and charging head.The details are shown in the figure below.The reliability of the chip on the mobile phone is high, and sometimes other power management functions are integrated (for example, Qualcomm’s charging IC is included in the Qualcomm Snapdragon chipset for downstream mobile phone manufacturers), so each mobile phone manufacturer will still use Qualcomm, TI, etc.Dachang’s products.Charge pump technology is relatively difficult, and currently there are three main products on the market that are adopted by mobile phone manufacturers.The highest rate of appearance is TI’s BQ25970, which is used in various products including VIVO and Huawei.Secondly, Qualcomm’s new SMB1390 for Xiaomi 9 may be used on a large scale in the Qualcomm platform in the future.Once again for NXP’s PCA9468, for the ASUS ROG Phone.In addition, many manufacturers including Dialog, Taiwan Liqi Technology have also launched their own charge pump chips.For charge pump chips, how to continue to increase their conversion rate at high currents is key.It is believed that with the popularity of charge pump fast charging, the charge pump chip will become a must for all major power management companies in the future.For the chip at the charging head end, all aspects are slightly lower than the mobile phone terminal, and it is an opportunity for small and medium-sized manufacturers and even start-up companies.The Qualcomm mobile phone chip is included in the Qualcomm Snapdragon chip, and the protocol control IC Qualcomm in the charging head is licensed to third-party manufacturers that meet the standards.Up to now, Qualcomm has authorized 17 products from more than 14 manufacturers.The Qualcomm QC4+ licenses include Cypress, Dialog, NXP, Diodes and other international manufacturers, as well as Taiwanese manufacturers such as Core, Gengyuan, Yiqun, Jingtuo, Tianzhu, Tongjia, Angbao and Weiquan.At present, only the British Central core company in the mainland has obtained Qualcomm authorization.Similar to Qualcomm, OPPO’s low-voltage fast charging solution also uses a third-party authorization method in the charging head-end protocol control IC.At present, VOOC flash charging certification includes Shanghai Nanxin Technology, Yingjixin, Zhuhai Zhirong Technology and Ruixin Microelectronics.Compared with the oligopoly of the mobile phone and the charge pump chip, the contending of the charging head-end chip is obviously more interesting.Let us zoom in on the charging head in the NXP fast charging scheme above. In addition to the protocol control IC, the other core components include MOSFET, transformer, PWM control IC, and synchronous rectification control IC.The author believes that there are three trends in the development of charging head-end chips in the future, one is higher voltage regulation accuracy; the other is the introduction of power devices such as gallium nitride; the third is higher integration.1. Higher pressure regulation accuracy.Higher voltage regulation accuracy means higher efficiency and lower heat generation.In the QC2.0 era, Qualcomm only supports 4V voltage regulation of 5V, 9V, 12V, 20V, etc. In the QC4.0 era, the voltage regulation range has been refined to 20mv.2. Introduction of power devices such as gallium nitride.As the power of the charging head continues to increase, its volume has also been increasing. How to reduce the volume of the charging head is also a key issue for the future development of fast charging.The answer to the volume reduction lies in the introduction of power devices such as GaN and high-frequency flat-panel transformers.The GaN MOSFET frequency can reach 500K-1MHz, which is 5-10 times higher than the original silicon-based MOSFET frequency.The higher frequency allows the larger volume of capacitors in the charging head to be multiplied, while the higher efficiency of GaN greatly reduces heat generation. With the smaller size of the high-frequency flat-panel transformer, the 44W charging head can be reduced toThe traditional 5W or 10W charging head is about the same size, which greatly enhances the portability of the fast charging head.3. Higher integration.A smaller size necessarily means a higher level of integration.The protocol control IC of Taiwan’s Lishun Technology, which is used in the 44W charging head of IQOO, has integrated the synchronous rectification control IC.Solutions that integrate protocol control ICs, synchronous rectification ICs, GaN MOSFETs, PWM control ICs, and flat panel transformers may occur.PI (Power Integrations) has integrated the primary switch, primary and secondary controllers, and detection components and alternative optocoupler FluxLink into a single IC in the recently released LYTSwitchTM-6 family of LED driver ICs.A similarly highly integrated solution in the future is very likely to appear on mobile phones.Where is the limit of mobile phone fast charging?As mentioned above, the core of fast charging is to increase the current during constant current charging. There is a limit to the charging current that mobile phone batteries can accept.Here we introduce a concept of battery charge and discharge C rate.For a 4000mAh 3C battery (currently used in flagship phones), the maximum allowable charging current is 4000mA*3=12A, corresponding to a theoretical maximum charging power of 60W.But in fact, often charging at the maximum charging current will also accelerate the aging of the battery and reduce the service life, so the 44W of IQOO is close to the limit of the 3C battery.If you want to continue to increase power and shorten the charging time, either use a higher C rate battery, or a dual-cell solution (such as OPPO’s Super VOOC flash).VIVO has integrated the above method in the Super Flash Charge concept machine released this year.It adopts 6C dual-cell series scheme, the maximum charging power can reach 120W, charge 50% in 5 minutes, and it can fill a 4000mAh mobile phone in 13 minutes.Apple will finally have a fast charge in 2019, but this may only be a start..
The thing that the phone is fast charging