Bench Talk

(Source: Alexander_Evgenyevich/Shutterstock.com)

Advanced features such as 5G and 4K displays in portable devices drive up power consumption—a lot more than 15W in many cases in devices operated by high-capacity 2S batteries. For these power-hungry gadgets, USB-C Power Delivery (PD) is a boon because it enables fast charging that gets these products back in operation with little downtime (Figure 1). Many applications that previously used AC-DC barrel adapters are migrating to USB-C PD for convenience and standardization. However, for designers, compliance with the USB-C PD standard typically requires complex firmware development and additional hardware components. Given the short distance and high voltage (20V) between pins, if the connector is inserted or disconnected at an angle, there is also a risk of damage. Indeed, both USB-C and USB-C PD specifications require a unique skill set because designing for them is not as straightforward as designing for legacy USB variants.

Consumer devices such as cameras, AR/VR systems, and wireless speakers lead the charge to USB-C and USB-C PD. On the horizon, applications in industrial and medical areas are quickly adopting USB-C and USB PD, as consumers are demanding the same level of convenience in their professional environments. We also see the USB-C standard used in point-of-sale (POS) devices, industrial scanners, and breast pumps. These are products that can ill-afford an extensive development cycle, given time-to-market pressures. In this post, we'll share tips to streamline the design effort for USB-C PD designs.

Figure 1: USB-C and USB-C Power Delivery bring the conveniences of fast data transfer and charging to portable devices. (Source: Golub Oleksii/Shutterstock.com)

USB-C and USB-C PD enable designers to realize the promise of a universal connector, providing the specifications for a reversible 24-pin connector for data transfer and power delivery. USB-C specifies 5V up to 3A (15W), while USB-C PD 3.0 specifies 5V to 20V up to 5A (100W). To design a charging system for USB-C, you'll need to:

• Address signal integrity and speed issues
• Connect to various legacy interfaces
• Make sure that your design can handle a wide range of voltages and currents, including starting up with a cold socket (0V until end-to-end detection is complete)
• Ensure that the charger and the port controller will be able to talk to each other when the USB-C charging source is plugged in
• Meet the shrinking size demands of products such as consumer devices
• Maintain thermal efficiency to minimize temperature rise

Meeting these challenges typically requires complex host-side software development for USB-C negotiation or additional parts such as external field-effect transistors (FETs) and external microcontrollers. However, charging system solutions are available that help minimize these challenges. One key feature is compliance with the protocols, as this will simplify the design implementation. Some solutions are also designed with event-based action scripts that make the customization process easier. Highly integrated circuits will eliminate the need for too many discrete components. Also, consider features that will help maintain reliable operation in harsh environments (varying temperatures or moist conditions, for instance).

Another consideration arises with the use of higher capacity batteries, which the power-hungry end devices need to support longer runtimes. Migrating from a 1S to a 2S battery increases the capacity without increasing the charging current. Because USB-C supports input voltages between 5V and 20V and 2S or 3S battery voltages fall somewhere in between, a buck-boost converter can help bridge the gap. See Figure 2 for a block diagram of a 2S battery-based application.

Figure 2: Block diagram of a 2S battery-based application. (Source: Maxim Integrated)

Maxim Integrated has a new pair of USB-C charging system solutions that provide out-of-the-box compliance with the USB-C PD 3.0 specification, eliminating firmware development and reducing development time by up to three months. Their compact footprint also reduces the solution size by half compared to competitive solutions. The MAX77958 USB-C and USB-C Power Delivery charge controller is responsible for doing away with the firmware step, thanks to its GUI-driven customization script, BC1.2 support, and configuration settings related to Fast Role Swap (FRS), Dual Role Port (DRP), and Try.SNK mode. The standalone device eliminates an external microcontroller, provides out-of-the-box USB-C PD 3.0 compliance, and enables you to customize operation for the end application without firmware development. The device is also designed to withstand harsh environments via features including 28V rating, V_BUS short protection to CC pins, an integrated analog-to-digital converter (ADC), and moisture detection/corrosion prevention.

The MAX77962 is a 3.2A USB-C buck-boost charger with integrated FETs for fast charging of high-capacity 2S Li-ion batteries. It provides a wide input voltage range (3.5V to 23V) for USB-C PD charging, requires no discrete FETs, and can be configured with or without an application processor. Peak efficiency is 97 percent at 9V_IN, 7.4V_OUT, 1.5A_OUT.

You can evaluate both parts with the MAX77958EVKIT-2S3, which demonstrates the MAX77958 autonomously controlling the MAX77962 charger with its I²C master feature.

Both devices are part of a broader portfolio of USB-C and USB-C PD devices that includes power-efficient chargers and converters, autonomous and robust controllers, and power path and protection ICs.

The Tips to Achieve Faster Design of USB-C Power Solutions blog was written by Bakul Damle and Sagar Khare and was first published on www.maximintegrated.com.