output power is limited by the system architecture, and the power demands on the VS1/2/3 voltage rails. A maximum current of up to 50 A per output rail sup- ports power outputs as high as 1,000 W for 3U and 2,000 W for 6U. When the shared pins are utilized with multiple supplies, there are no real limitations on achievable power levels.
What about the other OpenVPX issues? Besides defining effective remedies to OpenVPX system power issues, VITA 62 also defines limits to myriad system-level issues such as the following.
Inrush current: This often occurs on initial system powering, where all mod- ules attempt to fully power the com- ponents on the boards. This creates an initial current surge on the power sup- ply, which, if not limited, could result in output rail voltages dropping below required levels. VITA 62 compliant sys- tems will provide VPX module design- ers tolerances on the amount of current that the module can draw in excess of their steady state requirements. In so doing, the architect of the VITA 62 com- pliant system will be able to correctly size the po wer requirements needed to be supported by the VITA 62 power
module(s). This will eliminate potential system issues where VPX modules can- not power up completely or are in an unknown state due to lack of current or undervoltage during initialization. This can lead to only certain board portions or certain components being properly initialized. These are challenging issues that can be difficult to detect and resolve.
Output control: The *ENABLE and *INHIBIT are input pins that control the output power generation. This allows sys- tems to support the use of an e xternal on/ off switch and the disabling of output rails.
EMI: Pertaining to EMI, VITA 62 pro- vides a set of guidelines for standards like MIL-STD-461F and MIL-STD-1275D, allowing board designers to specify their compliance to these specifications and how they have been met. Power supply vendors are free to provide onboard emis- sion control, or to define requirements for external components.
Synchronization: Synchronizing power supplies is a recently discovered require- ment for high-speed data acquisition systems. These systems typically need to synchronize data acquisition sam - pling times with power-supply switching times. VITA 62 allocates pins to allo w
the routing of synchronization signals to modules that require this capability.
Nuclear detection: The system also defines pins for use in nuclear detection. These systems typically need to cro wbar output rails on detections of an e vent. VITA 62 allows for both internal and external use of detection devices to sup- port this capability.
Putting it all together The existing VITA 46 key pins and key- ing definitions are used for VITA 62. This provides a means to identify up to five unique input powers. These keys will pro- tect against the accidental plugging in of an incompatible power supply card. The 3U connectors provide two keying pins, and the 6U has a set of three k eying pins. A single key on each connector def ines the input voltage setting of the power sup- ply. The keys and connector are designed to accommodate the use of liquid-cooling connectors as replacements for standard keys. The middle key is used on a 6U con- nector as the key for input power. This will accommodate the use of liquid-cooling quick connects as replacements for the outer keys’ pins. Figure 2 shows the final configuration of a 6U conduction-cooled module. The module is fully compliant with the VITA 48 mechanical profile.
VME and Critical Systems / Spring 2011 21
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