Days before Xiaomi 12 Series’ launch, Xiaomi continues to reveal more about its new flagship lineup. From the release of the first generation of fast charging by Xiaomi in 2019 to the extremely fast-charging system on MIX 4, Wired charging speeds increased by 7.5 times and wireless charging speeds have increased by 12 times.
Now with current devices on the market, included chargers can fully charge the phones in 15 minutes. With this increase in charging speeds and decrease of charging time, smartphone users’ habit of charging overnight changed to charging on the fly.
In order to achieve high speeds of charging, Xiaomi set fast charging as an important strategic direction in 2019. Xiaomi established four different Research and Development centers, In three years Xioami applied for more than 800 patents and released millions of devices equipped with fast charging systems.
120W single-cell solution to improve battery life, lightness and thinness
Smartphones with a wired charging speed of up to 120W use a dual-cell system without exception. The price of high-speed charging is to reduce the utilization of the internal space of the phone. The dual-cell battery when compared to a single-cell battery, capacity is about %3 to%4 lower than a single cell, even more than that dual-cell batteries need another chip for charging and because of this efficiency will result in a waste of %3 to %4 of power.
A single-cell battery can fix these problems but it faces a huge challenge to increase charging power above 100W. The goal of the Xiaomi is to achieve the best balance between battery life and charging performance and to achieve single-cell 120W wired fast charging.
Surge P1 and the 120W single-cell fast charging
In the past single-cell fast-charging solutions, to convert 20V voltage input to the device into a 5V voltage, a series of a parallel circuit of 5 different charge pumps is required. Because of this the circuit produces lots of heat, it is impossible to charge at full power for a long time and it is even more difficult to achieve 120W fast charging, which is unacceptable for Xiaomi.
To redesign the entire charging architecture, it is necessary to redefine the function of the fast charging chip. The core of Xiaomi’s 120W charging is two self-developed smart charging chips; known as Surge P1. Surge P1 takes over the complex structure of the traditional 5 charge pump and converts the high-voltage power input to the mobile phone into a large current that can be directly charged to the battery more efficiently.
As the industry’s first discrete charging chip, Surge P1 has an ultra-hight efficient architecture. The efficiency of the resonant topology is as high as 97.5%, the efficiency of the non-resonant topology is 96.8%, and the heat loss is reduced by 30%.
Surge P1 undertakes a lot of conversion work: traditional charge pump voltage converters only need two working modes (transformation, pass-through), while Surge P1 needs to support 1:1, 2:1 and 4:1 conversion modes, and all modes need to support dual conduction, which means a total of 15 permutations and combinations of mode switching control, 7 times more than traditional charge pump voltage converters. The 1:1 mode makes the screen on charging more efficient, the 2:1 mode is compatible with more chargers and the 4:1 is needed for 120W charging. Reverse 1:4 and 1:2 modes support high-power reverse charging.
4:1 charging chip with the highest charging efficiency and the most difficult design
At the same time, Surge P1 is also the 4:1 charging chip with the highest charging efficiency from Xiaomi, which can achieve an ultra-high power density of 0.83W/mm², LDMOS also reaches the industry-leading ultra-low 1.18mΩmm² RSP. The Surge P1 chip needs three different FLY capacitors with different voltage resistance. each capacitor needs an independent short circuit protection circuit and each operating mode needs to strictly control the precharge voltage, the number of power tubes is close to two traditional charge pumps, and because of the increase in topology design and functional complexity, each Surge P1 needs to pass more than 2500 tests before leaving the factory, which is much higher than the traditional charge pumps.
Conclusion
In the end, with the Surge P1 chip‘s help, Xiaomi is able to simplify the charging circuit and at the same time, the ultra-high efficiency of Surge P1 means that heat generation will be less and the full power charging can continue for a longer time. The upcoming Xiaomi 12 Pro is the first smartphone from Xiaomi to be equipped with Surge P1. It supports 120W wired charging, 50W wireless charging and 10W reverse wireless charging. In the fast charging industry, Xiaomi is ahead of other manufacturers, using self-developed charging chips. We will know more about Surge P1 and its capabilities on December 28!