USB 3.1 and Type-C

Author : Rich Miron, Digi-Key Electronics

29 March 2016

Figure 1 - USB Type-C Receptacle Pinout Diagram

The Universal Serial Bus (USB) standard, developed in the mid-1990s, standardises the connection between peripherals and computers to both communicate and supply power. 

It resulted in replacing a variety of interfaces such as serial/parallel ports, PS/2, and separate power chargers for portable devices.

Figure 2 - Suggested USB 3.0 PCB Layout Diagram using 3 components (Courtesy Comchip Technology)

USB 3.1/Gen 2 is pretty much just USB 3.0 with double the speed (10 Gbit/s). It is not reversible, so the connector and receptacle have to be aligned in the correct orientation for insertion. Similarly, USB Type-C has a speed of 10 Gbit/s but is reversible with 24 symmetrical pins so the connector can be inserted in the receptacle in either orientation. The use of the additional pins is required to support data protocols such as PCI Express, DisplayPort 1.3, and Base-t Ethernet using Type C cables. The pinout diagram of USB Type-C cable is shown in Figure 1.

Figure 3 - Suggested USB 3.0 PCB Layout Diagram using 2 components (Courtesy Comchip Technology)

The USB standard defines three connector sizes - standard, mini, and micro, type ‘A’, ‘B’, and ‘AB’ connectors and corresponding receptacles. The connector and receptacle used for USB Type-C are smaller sized (similar to Micro-USB) and more durable than its predecessors, rated to 10,000 insertion/removal cycles. To enable faster charging of portable devices, such as tablets and smart phones, the cable supports a USB power delivery mode of up to 100 W.

Figure 4 - Suggested USB 3.1 PCB Layout Diagram using 3 components (Courtesy Comchip Technology)

USB port protection requires low capacitance ESD surge suppressors which can be supplied by Comchip Technology. The suggested PCB layouts are shown in Figures 2 and 3. Similarly, suggested parts and layouts for USB 3.1 are shown in Figures 4 and 5. The Type-C suggested flow-through PCB layout is shown in Figure 6.

Figure 5 - USB 3.1 Suggested PCB Layout Diagram using 2 components (Courtesy Comchip Technology)

USB 3.1 Type A has similar ESD requirements to USB 3.0 Type A, so the suggested PCB layouts are the same, except lower capacitance ESD components are recommended. Suggested PCB layouts for USB 3.1 are shown in Figure 4 and 5.

Figure 6 - Suggested USB Type-C PCB Layout Diagram with Flow-Through Design (Courtesy Comchip Technology)

Since there is a 10 Gbit/s throughput for USB type-C, ESD protection is essential because of the potential impact of additional capacitance and inductance on the high-speed differential pairs. USB Type-C has increased ESD protection requirement due to the reversible connector design.

In this instance, a flow-through design featuring Comchip’s DFN10P package will simplify PCB layout by placing the package on top of the high speed differential pair, this avoids complicated vias or loops and saves PCB space. The recommended parts for USB Type-C are shown with the suggested PCB layout shown in Figure 6.

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