A good target for a USB 3.0 switch should be >2.5 Gbps. This is trivial for USB 2.0 at 480 Mbps, but significant for USB 3.0’s 5 Gbps. Maximize 3dB bandwidth: A common industry convention is to measure the max signal frequency of a channel at the 3dB loss point. Besides the fanout of the switch, there are a number of key parameters that characterize them.įigure 1: A charge pump-enhanced NMOS transistor is at the root of USB signal switches. Adding a charge pump widens the rail-to-rail output voltage and allows a higher Vdd operating range while still maintaining moderate ~250μA power consumption (Figure 1). The basis for a USB switch is an NMOS transistor that’s suitable for hot-swap/plug applications and fast switching. Let’s keep it simple for now in this short primer. Protocol switches also exist-and our sponsor Pericom Semiconductor makes a ton of them-but they deal with additional layers of the stack and can interface to more than just USB for example, they can also switch PCI Express and USB. The former are concerned mostly with the electrical physical layer (PHY) of the OSI model. We’re confining our discussion to signal switches as opposed to protocol switches. ![]() Switches used for USB 3.0 are backward-compatible with USB 2.0 signals, but not vice versa. The four backwardly compatible USB 2.0 pins are cleverly integrated into the upgraded seven pin 3.0 Standard A connector. The common, large USB Standard A connector is the end inserted into a USB hub, looks similar for USB 2.0 and 3.0, but is labeled “SS” (Super Speed) for 3.0 and is backwards compatible into USB 2.0 slots. USB 2.0 has four pins, while USB has nine (Tables 2 and 3). Table 1: USB switches are used extensively for USB 2.0/3.0 channels, and designers should be concerned about signal integrity (SI) with 3.0’s speed. While USB 1.1 and 2.0 are relatively low speed, the 5 GHz frequency of USB 3.0 presents some signal integrity challenges, as we’ll see later (Table1). The most common switch configuration is a 2:1, although other configurations are possible such as Pericom Semiconductor’s PI2USB4122 4:1. We’ll stick to USB 2.0 and 3.0 since they make up the bulk of the market.Ī USB switch is basically a MUX/De-MUX that bi-directionally moves USB signals between multiple ports and maintains adherence to USB-IF specifications. ![]() I’m going to tell you three things you need to know about USB switches-the digital MUXes and crossbars that fanout USB signals as part of most embedded designs. And every one of Apple’s recently announced ultra-slim MacBook will sport the very latest-and wickedly flexible- Enhanced SuperSpeed USB 3.1 Type-C connector. It’s tough to forecast how many USB 2.0 (480 Mbps) or USB 3.0 (5 Gbps) channels there are in the world because USB is (nearly) as ubiquitous as LED lights.īut looking at some ultra-mobile devices that contain USB gives some idea just how popular USB is: 317million PCs, 321 million tablets, and 2 billion mobile phones (source: Gartner Device Shipments, July 2014). If you’re designing with USB 2.0 or 3.0, you need to know these three things about moving USB signals around your system.Ĭhances are you are now-or soon will be-designing USB into your embedded system. Ciufo, Editor-in-Chief, Embedded Intel Solutions magazine ![]() Not just perfect for the Raspberry Pi, this cable will also work with anything that has a USB-C port, however – this cable does not transfer data – so it’s mostly just good for powering and charging devices – but adding an on/off switch to your power supply is a nice addition and one that we absolutely love clicking.Chris A. The entire cable (including connectors) is just 31cm long so it’s never far from your Raspberry Pi. The cable is USB-C female one end and USB-C the other, meaning you can continue to use your official Raspberry Pi power supply with the added benefit of a power switch. Note: This is designed and tested for the Raspberry Pi 4. To turn your Raspberry Pi back on again, just click the switch – simple! The switch has a nice rubber feel and a solid ‘click-on-click-off’ action, and includes a little red LED power indicator.
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