Smartphone USB 2.0 port sharing implementation

Power Bank Charger / Universal Laptop Charger / Multi-port intelligent A-port hub

Typical smartphones include a communication processor, an application processor, and a power management IC. They must share a single USB port and communicate at a high -speed USB data rate of 480Mbps. Many mobile devices need many signal processing integrated circuits (IC) to meet the different functional requirements of users. All kinds of novel things are making smartphones more and more entertaining. Without better applications, it will fall behind, and market sales are not ideal. This article introduces some solutions that can solve this problem and compare various different solutions from USB hubs to simple simulation switches.

USB is "Universal Serial Bus". The Chinese name is the general serial bus. This is a new type of interface technology that has gradually been widely used in the PC field in recent years. The USB interface has the characteristics of faster transmission, supporting hot insertion and connecting multiple devices. It is currently widely adopted among various external equipment. There are currently two USB interfaces: USB1.1 and USB2.0. In theory, the transmission speed of USB1.1 can reach 12Mbps/second, while USB2.0 can reach 480Mbps/second, and can be compatible with USB1.1 downward.

Mobile devices require many signal processing integrated circuits (ICs) to meet a variety of functional requirements of users. A typical smartphone includes a communications processor, an application processor, and a power management IC that all must share a single USB port and communicate at a high speed USB data rate of 480 Mbps.

Dedicated to some solutions to this problem, and a variety of different solutions from USB hubs to simp le analog switches.

One way to design a smartphone is to have an internal power management device that controls a single USB 2.0 port, which can be done by turning the USB 2.0 port to itself using a 3:1 multiplexed USB switch. By default, it can also be turned to an application processor for most multimedia functionality (such as MP3 playback or video processing). It can also be turned to a communications processor for radio communication for data access or calls (see Figure 1). This architecture has the advantage of allowing the phone to go to sleep when the function is not in use. In addition, the power management unit can wake up the associated processor when USB 2.0 port activity is detected, or when any processor needs to use a USB port. After the USB socket is first inserted, the power management IC can also interrogate the USB line to determine if there is a dedicated USB charger or charging master port connection to directly charge the battery through the VBUS signal. When communicating with a USB host device (such as a PC), the physical layer (PHY) within the communication and application processor uses the 480 Mbps full high speed data bandwidth of the USB switch.

For most integrated circuits, high speed and low power are generally a pair of contradictory features. A solution that combines both often requires lowering the voltage and using a fine geometry process size; however, the USB specification requires a high voltage signal. In a robust handset design, the D+ and D- signals can withstand shorts to the 5V VBUS signal line, limiting the low voltage solution. However, the recently introduced low-power charge pump USB switch solves this problem and meets the stringent USB transmit eye diagram requirements, as shown in Figure 3. In fact, there is no need to make any modifications to the architecture or selected devices, and most of these designs can operate at speeds up to twice the high-speed USB data rate (> 1 Gbps).

To switch from one processor to another via a USB switch, you first need to disconnect all paths and then allow enough time to ensure that the USB host port controller recognizes a disconnect and switches to another path. This way, the master device can be reset and the new USB device can be reset. All of this is done on the phone using software and requires the involvement of a software engineer to write the software according to the constraints of the selected hardware. However, the more advanced USB switches now allow more use of portable device software, so the aforementioned methods are gradually being phased out. This is because any change in the selection control signals of these USB switches will automatical.