How to introduce the characteristics of USB PD into mobile power supply design?

An example of this is the USB Type-C; USB Type-C is designed to create a standard interface for high-speed data transmission and power transmission, requiring only one cable to replace the need for multiple cables. This makes sense, in part because electronics manufacturers are reluctant to provide cable for every device they ship, and because consumers are dealing with a large number of "backup" cables that are left unused in drawers, cabinets, and desktops.

 

However, standardizing a specification does not mean that all devices are created identically. Protocols that support USB 3.x powering also enable vendors to communicate with devices using a so-called Vendor-Defined Message Mode (VDM) through a Configuration Channel (CC). With VDM, vendors can exchange more than the information defined by the USB 3.0 power supply specification. It can be used for a variety of things, but it also means that manufacturers can communicate directly with their own devices. This device appears as a standard on any other device, but adds added value to customers, such as customers who use wall adapters specifically designed for their phones.

 

Accessing the VDM for use in a USB controller will further increase the appeal of USB Type-C connections, enabling functions such as faster charging or putting the device into standby or assist mode to be able to reuse certain connections to accept non- USB protocol.

 

These features will create new applications for USB, especially in terms of power. Continued driving ultra-low power processing means more work can be done with less power, and since the total power of the USB connection is now 100 W (Figure 1), this opens up a variety of possibilities. But to achieve this potential, you need a USB controller that can budget.

power usb

Part 1, fast charging

The power supply specification works with existing battery charging specifications, but brings additional benefits when using VDM. Most notably, it supports Qualcomm's fast charging function, based on the choice of Snapdragon processor, which provides higher power and provides a faster charging cycle for smartphones. This technology is also approved for use by other manufacturers. Several charging protocols are currently in use, such as Motorola's TurboPower charging technology, MediaTek's Pump Express and Samsung's adaptive fast charging technology.

 

When do not using a compatible power adapter, the smartphone will default to a lower power setting, but when it is used with the manufacturer's own/approved charger, the user will be able to charge faster. Although different manufacturers have different specifications, the USB 3.1PD specification can provide up to 27W between 5V and 12V.

 

To help consumers choose the right solution, the USB Developer Forum (USB IF) has extended the USB charger specification and Logo program to include a USB fast charger. The charger certified by this program supports the Programmable Power Supply (PPS) feature of the USB PD 3.0 specification.

 

Part of the appeal of the PD is that it supports USB-powered devices to negotiate with the power supply, providing only the amount of power required. This includes devices that require less power than the default settings, which means that the power supply can power more devices, share power between devices, and provide more than just power to the device. For example, the display provides power and communication channels for laptops and external hard drives, allowing notebooks to access hard drives through the display.

 

Part 2, mobile power

The battery charging feature provided by the USB interface is ubiquitous and has been used by mobile power manufacturers for many years. While mobile power supplies provide a convenient way to get extra power away from the outlet, the transition from battery charging to power transmission will require a new generation of mobile power. Supporting the variable power provided by the PD introduces a degree of complexity that is not compatible with existing mobile power supply designs that typically use a simple universal power management IC or regulator.

 

To support all of the PD's features, including fast charging with VDM, mobile power manufacturers will need to turn to designing an intelligent controller to provide the functionality provided via USB PD. For example, LC70501F from ON Semiconductor. This highly integrated Flash-based configurable device brings together all the features you need to manage the power provided by a Li-Ion battery through multiple USB ports. Figure 2 shows a typical application example.

pcb voltage table

 

With firmware developed by ON Semiconductor, the configuration can also be extended to use VDM mode, so manufacturers can add additional value, such as implementing fast charging technology.

 

It directly drives an external MOSFET to provide a scalable power supply, while its switching controller produces the required voltage, from 5V to 12V. All PD features are supported by the selection of an appropriate external MOSFET, including the Fast Charge 3.0 High Voltage Dedicated Charging Port (HVDCP) Class A. The Buck/Boost topology enables the mobile power supply to have a USB Type-C dual role port (DRP) and USB BC 1.2, and also includes a battery status feature that uses four LEDs to indicate battery power. Utilizing the features of USB 3.x, smartphone apps can provide more information about mobile power, such as state of charge, charge cycle, and charge and discharge times.

 

ON Semiconductor provides evaluation boards to help manufacturers design and import the LC709501F and select the most suitable firmware. For example, the FW02 supports one Micro-B input, supports Type-A output on two channels, fast charging 3.0 HVDCP, Boost auto-start and external Boost IC for further power output, while FW05 supports DRP and Type-A The Type-C output is just like the one we used for Boost auto-start and external boost. More firmware versions are under development to support additional configurations. Figure 3 is a functional diagram provided by the FW05.

Working principle diagram

By directly supporting four LEDs to display battery power, manufacturers do not need to add an additional microcontroller, saving bill of materials (Bom) costs and reducing design complexity. The evaluation board (part number LC709501EVA05GEV) implements the FW05 and supports four modes, as shown in Figure 4.

Working principle diagram

Part 3, a new controller

The introduction of USB Type-C and PD will bring huge benefits to consumers and manufacturers, but because developers need to learn how to access new features and the requirements of the engineering team, it will take some time to adjust.

 

Developing a mobile power supply that fully supports PD, including multiple outputs and fast charging, will require a new controller developed with USB 3.x as the core. The LC709501F is part of a range of devices to make USB PD simpler and easier for developers to access, and it offers unsurpassed integration. Its ultra-low quiescent current of only 15μA, plus the need for an additional microcontroller, means it offers all of these features while consuming the least amount of battery power.

 

The ability to configure controllers through vendor-defined message patterns is another advantage over controllers with fewer features, enabling manufacturers to differentiate their products while still fully complying with the USB IF specification.

pcb table