USB-C Power Management Design

Tue Jun 20 15:26:09 CST 2023

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USB-C Power Management Design

Applications and portable devices with a USB Type-C interface are increasingly common today. USB Type-C (USB-C) connectors offer many advantages such as small size, ease of use, versatility, and support for multiple protocols such as USB 3.1, DisplayPort, HDMI, and USB PD.

The USB-IF has published a USB Type-C guide known as the USB Type-C cable and connector specification, which outlines the USB Type-C standard that can achieve its versatility.

This article will discuss the USB Type-C specification and how to design a simplified power supply solution to meet the necessary requirements for powering portable devices and accessory applications.

The USB Type-C specification defines four pairs of power pins for supplying power, and two CC pins for detecting device status. It defines two potential power supplies: VBUS and VCONN. The VCONN pin has no special specifications, as its voltage is always between 3V and 5V; however, VBUS has a wide voltage range and must comply with different protocols, such as USB PD. With the USB PD protocol, VBUS voltages can be up to 20V. C cable and connector specifications require that the pins connected to VBUS be able to withstand voltages up to 21V.

Both VCONN and VBUS can provide power to a USB cable with a powered tag. If VCONN is available and can be detected, the connected device is powered by VCONN. If VCONN is removed, the device is powered by VBUS. To monitor the availability of these two power paths, the system requires an O-loop to detect power changes. The diagram below shows a traditional O-loop. The circuit has four I/O pins, two power input pins (VIN1 and VIN2), an output power pin (VOUT), and a select pin (SEL). When the SEL pin receives a signal, the internal logic controller generates two control signals to select the power path from VIN1 or VIN2.

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Let's take an example of an application of a USB Type-C cable with VBUS connected to VIN2 and VCONN connected to VIN1. When Q2 is on and Q1 is off, a current (IS) is generated between VIN2 and VIN1 due to the MOSFET body diode. In this setup, the VBUS voltage can be as high as 20V, which means that any device connected to VIN1 can be damaged.

To solve this problem, four MOSFETs (one pair of back-to-back MOSFETs for each of the two paths) should be used to achieve an optimal O-loop (see figure below). The circuit uses two MOSFETs as one switch. Since the body diodes of the two MOSFETs are in opposite directions, no leakage current is generated regardless of which switch (switch 1 or switch 2) is on or off.

Using four N-channel MOSFETs (Q1, Q2, Q3, and Q4) to create two switches and build an O-loop allows for fast transients on both power pins (VIN1 and VIN2) while allowing for power path selection via the SEL pin.

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The USB Type-C cable and connector specification clearly defines that devices powered by VCONN and most ICs with powered tags require either 3.3V or 5V. To ensure a stable output, whether the input voltage is above, equal to, or below the output voltage, a Buck-Boost circuit is required to handle it. Building a Buck-Boost circuit with four MOSFETs provides faster transient response and high efficiency. To balance space and efficiency requirements, two P-channel MOSFETs and two N-channel MOSFETs can be used to build a Buck-Boost circuit. 

The USB Type-C cable and connector specification provides a reference design for USB Type-C cables with limited electronic design space. The most effective way to design in a smaller space is to utilize a highly integrated power solution.

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Conclusion

The USB Type-C cable and connector is versatile and powerful despite its small size, offering two sources (VCONN and VBUS) and a wide voltage range. An integrated power supply device with O-loop and Buck-Boost circuitry is highly recommended for a compact, compact design that reliably handles and monitors USB Type-C voltages. The circuit topology with integrated O-loop and Buck-Boost circuitry is also suitable for both multi-input power applications, such as those with USB and battery input sources (e.g., Li-ion battery input). The ideal solution not only handles both voltages efficiently, but also integrates the O-loop and Buck-Boost circuits into a single device to minimize board space and BOM costs. With its high level of integration and built-in protection, the MP5416 is a differentiated power supply device for accessory products with USB Type-C inputs, such as USB Type-C digital AV multi-port adapters and USB Type-C to HDMI adapters.

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By HornmicLink_Mia.J @230620 15:28