Texas Instruments manufactured HD3SS3412RUAR as an analog differential switch for special-purpose devices, especially PCIe devices.
In this article, you will learn about this differential switch’s capabilities.
How Does a Differential Switch Work?
A differential switch is also called the differential pressure switch. It works by noticing the pressure or voltage differences between the two points in a system; in this case, a circuit board.
Once the pressure or voltage differences are noticed, the switch helps to balance the differences by switching to the channel that follows the predefined value.
Now, HD3SS3412RUAR works in a similar way, especially with the use of a high-speed switch capable of switching up to four (4) differential channels. That way, it can help these multiple channels to establish multi-connections.
The Analog Switching Capability
HD3SS3412RUAR is an analog switch for special-purposes. What this means is that it doesn’t always tow the path of conventional (general-purpose analog switches), which serve all purposes.
Due to the special designation, HD3SS3412RUAR’s analog switch with special-purpose uses is ideal for routing signals via a dedicated Solid State Device (SSD). The routing also includes provisions for special features and functionalities that are hitherto, missing on the general-purpose analog differential switches.
Multiple Switching Capabilities
HD3SS3412RUAR supports the switching of purposes across multiple paths. For example, using the high-speed passive switch capable, the switch can support the following:
- Four (4) differential channels
- Support for two full PCI Express (PCIe) x1 lanes from one source to up to 2 target locations inside a server application or PC.
- It also supports applications that enable connections between multiple source devices. An example of this types of devices is a shared peripheral between two platforms.
Multi-Interface Support
Interfaces play a role in the connections established with a differential switch. HD3SS3412RUAR’s supports multiple interface standards.
Common Package Footprint
HD3SS3412RUAR is one of the ideal differential switches for circuit boards and consumer electronics with limited space.
It is because of the common package footprint, optimized into the small 3.5-mm x 9.0-mm, 42-pin WQFN package.
This package is also available in a common footprint, shareable among many vendors.
Excellent Signal Conduction
Conducting the signals from one channel to the other might not always be simple. Therefore, using a mechanism to regulate that is very essential. That is the reason for integrating a Single Control Line (SEL pin) inside HD3SS3412RUAR. This pin aids the control and conduction of signals from one path or channel to the other. It can also be used to conduct the signals backwards.
Full Temperature Operation
HD3SS3412RUAR also supports the temperature use from a single supply voltage of 3.3 volts up to a full operating temperature of 85˚C.
Technical Attributes
The table below represents the technical attributes of this differential switch:
| Attributes | Description |
| Mounting Style | Surface Mount Technology (SMT) |
| Typical Application | PCI Express (PCIe) |
| Core Feature | Bi-Directional |
| Number of Channels | 4 |
| Package/Case | 42-WFQFN Exposed Pad |
| Operating Temperature (minimum to maximum) | Between 0˚C and 70˚C |
| Multiplexer/Demultiplexer Circuit | 2:1 |
| -3db Bandwidth | 8GHz |
| On-State Resistance (Maximum) | 80hm |
| Voltage – Supply, Single (V+) | Between 3 volts and 3.6 volts |
HD3SS3412RUAR Application Considerations
HD3SS3412RUAR is ideal for the PCI Express (PCIe) Gen III applications; examples being the following:
- Shared I/O Ports
- Desktops and notebooks PCs
- PCI Express (PCIe) backplanes
- Storage area networks and servers
However, there are more applications or use cases for this differential switch. It can also be used with other high-speed data protocols, especially if those protocols have up to <1800 mVpp of differential amplitude and a common-mode voltage of <2.0 volts.
It also supports the DisplayPort 1.2 and the USB 3.0 applications.
AC Coupling Caps Consideration
Considerations are also to be made for the AC Coupling Caps. HD3SS3412RUAR’s optimization for this is to offer the 0603 capacitors and the 0402 capacitors.
You must avoid using the C-packs or the 0805 size capacitors, but stick to the above.
With that being said, optimizing the capacitors involves setting and matching the value of the 0.1 µF capacitor with the ± signal pair.
To ensure a symmetric placement of the AC Coupling Capacitors (Caps), it is better to do that along the TX pairs. Do that by placing the caps on the top-routed TX pairs on the system board.
Although the above is one of the best ways to place the capacitors, there are a number of other options worth exploring. See them below:
1. Coupling the Capacitors on the Both Sides of the Switch
The AC Coupling Capacitors can be placed on both sides of the HD3SS3412RUAR differential switch.
Doing this is required only when the common-mode voltage on the system board is above 2 volts.
As a way of balancing the performance, the less than 2-volts biasing voltage is to be used alongside the common-mode voltage.
2. Capacitors’ Placement between the Switch TX and the Endpoint TX
HD3SS3412RUAR’s AC Coupling Capacitors can also be placed between the switch and the endpoint TXs.
The placement has to be balanced with the biasing of the switch by either the host controller or the system.
3. Placement on the Host and Endpoint Transmit Pairs
This is the third configuration option for HD3SS3412RUAR’s differential switch’s capacitors. In this case, the AC Coupling Capacitors are placed on both the host transmit pair and, on the endpoint, transmit pair.
The performance is further balanced with the biasing of the lower switch with the host controller and that of the upper switch by the endpoint.
Concluding Thoughts on HD3SS3412RUAR
HD3SS3412RUAR is a high-performance differential switch, capable of switching the performances and signal transmission across 4 channels. With the bi-directional (MUX/De-MUX) type of differential switch, it facilitates the routing or transmission of high-speed signals between two locations on a circuit board.
However, note that the HD3SS3412RUAR is optimized for special-purpose differential switching applications, most especially the PCI Express Gen III applications. Also, you can use it to route or switch signals in a couple of selected high-speed data protocols and applications. Other than that, it is not to be used with any other (unsupported) application.
Lastly, take note to use the accurate AC Coupling Capacitors’ placement so you don’t distort the signal routing process.
