In the past decade, as mobile phones have become more integrated, batteries have evolved into non-removable components. With battery capacity technology not making significant breakthroughs, fast charging technology for mobile phones has emerged. Fast charging technology enables batteries to be charged to full capacity in a short period, dramatically reducing charging times and significantly enhancing user experience. Achieving fast charging inevitably involves inputting substantial energy into the device. However, people's awareness of the drawbacks of high-energy fast charging technology often centers on battery damage and frequently overlooking the EOS problem.
High-Energy Fast Charging Technology
Fast charging for mobile phones is the pioneering application of fast charging technology. The technology has now become widespread across a range of electronic products, including computers, wearable devices, and portable power banks. Taking mobile phones as an example, there are currently several mainstream fast charging technologies available, including QC charger, USB-PD, and proprietary fast charging technologies from various phone manufacturers such as Huawei's Supercharge, VIVO's Dual Engine Fast Charging, OPPO's VOOC, and Xiaomi's Super Turbo. Regardless of the different fast charging technologies, the principle is to increase charging voltage or current to increase charging power, thus achieving fast charging functionality.
OPPO SuperVOOC, the Super Flash Charge technology, employs a combination of low voltage and high current, along with a novel constant voltage charging algorithm, which is a direct charging solution by dynamically controlling constant voltage and constant current at the adapter. In the high current charging mode, the charger directly delivers current to the battery through a direct charging switch. The charging voltage is increased via a series connection of dual cells. Via Voltage Open-Looped, a Multi-Step Constant-Current output is realized. The “Voltage Open-Looped “is a component designed based on negative feedback principles, the technology controls the voltage and current during the battery charging process. When the charging current surpasses a predetermined threshold, the Voltage Open-Looped automatically activates the circuit's switch, reducing battery voltage while maintaining a constant charging current. This mechanism enables Multi-Step Constant-Current output to effectively enhance charging efficiency and safety. Consequently, it can elevate terminal charging power, with charging power reaching up to 125W (20V/7.5A).
Huawei's Super Charge utilizes charge pump technology. Taking the Mate 50 as an example, it supports up to 66W Super-Fast Charging, which is the third generation of the technology, known as the 2x SCP Fast Charging Technology (11V/6A). The second generation was a 1x voltage fast charging (5V). The third generation is upgraded to 2x voltage with 10V or 11V. Among the common charging specifications: the SCP 66W Fast Charge (11V/6A) optimizes efficiency by setting the maximum current and voltage to 6A and 11V respectively. This technology employs a charge pump principle to overcome the limitations of Type-C current. It directs energy through a 6A channel into the mobile phone. And after entering Type-C, it utilizes the charge pump to lower the charging voltage to around 5V, simultaneously raising the current to 13.2A from 6A. This method is used to charge the battery with the 5V/13.2A low voltage and high current. Huawei's fourth generation of Super Charge: the 4x SCP Fast Charging Technology supports 100W charging (20V/5A).
EOS Hazards in Mobile Charging End
For various fast charging technologies, power levels are consistently increasing. In 2021, the USB-IF association introduced the new PD3.1 standard, raising the maximum charging power from 100W to 240W. Various mobile phone manufacturers have also announced their 240W fast charging technologies. Charger output voltages need to be elevated from 5V to 9V/10V/12V, and even higher to 20V. Given the diverse and complex charging environments for global mobile users, even basic 5V/1A charging is highly susceptible to EOS damage. Furthermore, the prevalence of non-original chargers and subpar charging cables with difficult-to-distinguish quality in the market and many developing countries’ unstable power supply voltages lead to a high likelihood of EOS occurrences during charging. Apart from this, present mobile users frequently engage in charging and unplugging actions due to their habit of frequent charging. This behavior can also lead to ESD damage issues. Since the process of high-energy, high-power fast charging involves high voltage, large current, and more component modules, EOS fluctuations will become larger and more frequent. Without an effective ESD/EOS protection solution for mobile charging, rear ICs such as PMUs and OVPs are at risk of damage, leading to mobile malfunctions.
The charging adapter serves as a significant source of high-energy EOS.
Frequent plugging and unplugging are susceptible to EOS strikes.
EOS Protection Solution for Charging
Since its establishment, Amazing Microelectronic Corp. has accumulated over a hundred patents in the ESD/EOS field. The company has gained recognition from major manufacturers for its focus on ESD/EOS protection. In terms of EOS protection for charging, the technology complies with testing requirements from major mobile phone manufacturers with the highest protection standard reaching EOS 450V (8/20μs, 2ohm). As depicted in Figure 1(a), the simplified circuit diagram of a mobile phone charging port. For Vbus protection, TVS1 can be added to the DC input (located near the interface, before OVP). For Vbattery protection, TVS2 is added to the positive terminal of the PMU. Apart from the OVP used to withstand direct current energy, the selection of TVS must be able to accommodate high-voltage DC inputs without damaging the PMU due to surge energy. Therefore, the first-level TVS1 in Figure 1(b) utilizes 15V, 18V, or 24V Surge TVS: AZ4715-01F/AZ4718-01F/AZ4724-01F, providing over Ipp 100A EOS protection capability. TVS2 employs 5V Surge TVS: AZ3205-01F, offering Ipp 100A EOS protection capability as the second-level defense, absorbing residual EOS voltage from the back-end. Both TVS levels provide low clamping voltage performance, effectively preventing EOS and blocking ESD interference. Practical and efficient second-level TVS protection significantly reduces the repair rate of charging defects and enhances mobile phone quality.
(a) Simplified Circuit Diagram of Mobile Phone Charging End
(b) TVS Model and Specification List
Overview of EOS Application Solution
For the mobile phone charging end, Amazing Microelectronic Corp.'s EOS protection solution combines the principles of mobile phone charging, ensuring no disruption to normal charging functionality and signal transmission. It effectively addresses issues related to frequent charging and complex usage environments, safeguarding mobile phones from EOS damage and significantly reducing incidents of mobile phone malfunctions. The combination of TVS and OVP forms a protective arrangement against DC and surge interference, making it the mainstream EOS protection solution in the mobile phone industry today.