Editor’s note: There area plethora of USB Type-C articles out there, but this is the first one I have seen with a really neat design architecture to shrink the board footprint with a high level of integration.
The new USB 3.1 Type-C standard is dramatically simplifying the way we interconnect and power our electronic gadgets. The standard utilizes the USB Type-C connector for data and power transfer between any two devices up to 100W. Accordingly, more functionality is required from the battery charging system, which tends to be increasingly smaller and lighter for every new portable device. This article reviews a typical USB Type-C charging system and shows how to simplify the design while delivering more power and more functionality in a smaller space.
USB-C Connector and Smart Phone
USB 3.1 Type-C Standard
USB 3.1 Type-C (a.k.a. USB-C) is a new standard which supports high data rates and increased power delivery between electronic products. USB 3.1 can deliver 10Gbps of throughput while delivering up to 3A over standard cables and up to 5A over enhanced cables. The bus voltage can be adjusted up to 20V (60W at 3A with a standard cable or 100W at 5A with an enhanced cable). Many notebook computers today require less than 100W of power, hence new models adopting a Type-C connector can be charged via a USB port the way small devices are charged today.
The complexity of the USB 3.1 Type-C standard requires a device to negotiate as either a power provider (source) or power user (sink) before power transfer takes place. The connectors at both ends of a Type-C cable are identical, allowing for reversible plug-in. Each connector is also flippable, which allows it to be plugged in with either side facing up. Type-C USB also allows for bidirectional power, hence a peripheral device can be charged, and the same device can also charge a host device. This promises to eliminate many proprietary power adapters and many types of USB cables, ultimately reducing the maze of wires surrounding today’s desktops.
Configuration Channel Detection
A new feature of USB Type-C is configuration channel (CC) detection. The configuration channel logic detects cable presence, orientation, and current-carrying capability. Cable detection occurs when one of the two CC lines is pulled down. Which line is pulled down (CC1 vs. CC2) determines the cable orientation. The current-carrying capability is determined by the values of the termination resistors. Another new feature of USB Type-C is cold-plugging, namely the 5V is provided only after successful end-to-end detection is completed. This feature makes CC detection mandatory in USB Type-C applications.
USB 3.1 Typical System
Figure 2 illustrates a typical portable power management front-end equipped to connect to a USB Type-C cable and powered by a lithium-ion (Li+) battery.
USB 3.1 Type-C Typical Power Management System
When the VBUS voltage is present it powers the charger, the system, and the rest of the blocks. In this phase, the battery is charged via QBATT operating as a current source. When the VBUS is disconnected, the battery powers the system via QBATT operating as a “on” switch.
With the USB Type-C protocol, the CC1 and CC2 pins (Figure 2) determine port connection, cable orientation, role detection, and port control. The charger in Figure 2 also supports the legacy protocol Battery Charger 1.2 (BC1.2).
The typical implementation of a battery system can be very costly in terms of Bill of Materials (BOM) and PCB space. Figure 3 shows the PCB size of the charger and detection section implemented with two ICs, one for the charger and one for the two detection blocks in Figure 2.
Common Integrated Solution PCB Size (61mm2)
The two-chip solution plus passives occupies 61mm2.
Highly Integrated Solution
Greater simplification of the BOM is achieved with a higher level of integration. In Figure 4, the blue highlighted box shows all the blocks that ideally can be integrated in a single power management IC (PMIC).
USB 3.1 Type-C Integration Path
With this level of integration, the system’s complexity is greatly reduced as shown in Figure 5.
Integrated Charging System