The current mobile terminal has a 5G connection, 4K ultra HD display, and other functions, which are often “power consumption”, far more than the conventional dual-cell battery energy storage. In the face of these high-power applications or devices, USB (PD) fast charge can quickly replenish power energy for terminals with its efficient charging capability. However, it is not easy for designers to adopt the USB PD protocol standard, often requiring complex firmware development and additional hardware design. For example, the short distance between the Type-C port pins and the high voltage (20V) can cause damage if the connector is inserted or disconnected at the wrong Angle. In fact, USB Type-C and USB PD specifications require designers to have hardware and software design skills, as well as a deep understanding of USB specifications.
As consumer electronic devices such as cameras, AR/VR systems, and wireless speakers gradually lead the development of USB Type-C and USB PD technology, how do accelerate the product launch process and shorten the development cycle? How to extend USB Type-C and USB PD technology to be widely used in industrial and medical fields? Here the author shares some tips to simplify USB PD design and help you get more done with less.
Design challenge analysis of USB-C Charging system
USB Type-C and USB PD provide symmetric 24-pin interface specifications for data transmission and power supply, enabling designers to design and implement generic interfaces. USB-c can provide 5V/ up to 3A charging current (15W), while USB PD 3.0 can provide 5V to 20V/ up to 5A supply current (100W). To design a USB-C charging system, consider the following challenges:
- Address signal integrity and speed issues
- Connect to a variety of traditional interfaces
- Ensure that the design is suitable for a wide voltage and current range, including support for the cold start (0V) until end-to-end detection is complete
- Make sure the charger and port controller can communicate with each other when plugged into the USB-C power supply
- Meet the small size requirements of consumer devices
- Maintain thermal efficiency and minimize temperature rise
To address these challenges, designers often develop complex mainframe software for USB-C or add additional components, such as external FETs and external microcontrollers. However, some fully compliant charging system solutions can greatly simplify the design implementation. Others are designed with event-based action scripts to make the customization process easier. At the same time, highly integrated IC will also streamline the use of a large number of discrete components. In addition, the designer needs to consider that the solution should be capable of maintaining reliable operation in harsh environments, such as varying temperatures or humidity conditions.
Another factor that must be considered is the use of high-capacity batteries, which are needed by high-power end devices to last longer. Compared to 1S batteries, 2S batteries can increase their capacity without increasing the charging current. Since USB-C supports input voltages between 5V and 20V, and 2S or 3S batteries are somewhere in between, a step-up converter can bridge the gap. FIG. 2 shows the schematic flow chart based on the 2S battery application.
USB-c compatibility out of the box
ADI’s new USB-C charging system solution meets the USB PD 3.0 specification, eliminates the need for firmware development, and cuts development time by three months out of the box. Its compact size can reduce the size of the solution by half compared to similar solutions. The MAX77958 USB Type-C and USB PD charge controllers require no additional firmware development, thanks to custom scripts that rely on GUI drivers, BC1.2 protocol support, and configuration Settings related to fast Role Switching (FRS), dual role ports (DRP), and try.SNK modes. This standalone product eliminates the need for an external microcontroller and provides out-of-the-box USB PD 3.0 compatibility, enabling users to customize the functionality of their terminal applications without having to develop a firmware. The product also features a 28V voltage rating, protection against CC pin short circuit to VBUS short circuit, integrated ADC, and humidity detection/corrosion protection for all types of harsh operating environments.
The MAX77958 can control the charger through its main I2C interface. The MAX77961 is a 6A step-down/boost charger with integrated FET for fast charging of large capacity 2S and 3S lithium batteries. It provides a wide input voltage range (3.5V to 25V) for USB PD charging, does not require discrete FETs, and can be configured with or without an external processor. When the input voltage is 9VIN, the output voltage is 7.4VOUT, and the output current is 1.5AOUT, the peak efficiency is 97%.
Interested parties can use the MAX77958EVKIT-2S6# (for 2S battery) or MAX77958EVKIT-3S6# (for 3S battery) to evaluate both devices. These two devices demonstrate how the MAX77958 uses I2C to control the MAX77961 charger.
The above ADI devices belong to the broad USB Type-C and USB PD device series. The range includes energy-efficient chargers and converters, durable automatic controllers, power channels, and protection IC, which can be freely combined.
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