5.0Gbps PCI Express Passive Switches
Applications Information
PCIe Switching
The MAX4888A/MAX4889A primary applications are aimed at reallocating PCIe lanes (see Figure 5). For example, in graphics applications, several manufacturers have found that it is possible to improve performance by a factor of nearly two by splitting a single 16-lane PCIe bus into two 8-lane buses. Two of the more promi- nent examples are SLI™ (Scaled Link Interface) and CrossFire™. The MAX4889A permits a computer motherboard to operate properly with a single 16-lane graphics card, and can later be updated to dual cards. The same motherboard can be used with dual cards where the user sets a jumper or a bit through software to switch between single- or dual-card operation. Common mode below 1V operation requirement.
Board Layout
High-speed switches require proper layout and design procedures for optimum performance. Keep design- controlled impedance PCB traces as short as possible or follow impedance layouts per the PCIe specification. Ensure that power-supply bypass capacitors are placed as close to the device as possible. Multiple bypass capacitors are recommended. Connect all grounds and the exposed pad to large ground planes. Common mode below 1V operation requirement.
| | DATA | MAX4888A/MAX4889A |
| | DIRECTION |
ONE LANE | MAX4888A | |
MAX4889A | |
NOTE: ONLY ONE LANE IS SHOWN FOR CLARITY | DATA IS ROUTED |
TO EITHER |
| | BOARD A OR B |
| A | B |
Figure 5. The MAX4888A/MAX4889A Used as a Single-Lane |
Switch | | |
Chip Information
PROCESS: CMOS
CrossFire is a trademark of ATI Technologies, Inc.
SLI is a trademark of NVIDIA Corporation.
______________________________________________________________________________________ 11
