VITA 62 brings COTS power supplies to VPX
Though VITA 46 (VPX) and VITA 65 (OpenVPX) systems are rapidly becoming a defense industry mainstay, a system-level interoperability standard for these systems’ power requirements has been a missing ingredient. However, the VITA 62 (Power Supply Modules) working group now aims to fill the void.
VITA 65 (OpenVPX) and VITA 46 (VPX) systems are revolutionizing the defense industry, having overcome initial system-level interoperability issues – for the most part. However, a system-level interoperability void still exists when it comes to power generation for these advanced systems. This gap has led to ad hoc power designs that are system specific but not interoperable between VPX systems. However, VITA 62 (Power Supply Modules) allows systems designs, using OpenVPX as a guideline, to specify power requirements for VITA 62 compatible systems. This will create an ecosystem of many VITA 62 products that are market driven for the large and growing VPX community.
Accordingly, the VITA 62 working group was started in September 2008 with the support of both module vendors and system integration companies. (It currently has about 40 participating companies.) The mandate of the committee is to provide a standard set of design guidelines for both hardware and systems to allow vendors to create power supply modules to power VPX systems. The development taking place in the VPX community and in the OpenVPX initiative has primarily focused on the development of modules, slots, and backplane profiles for applications, with little emphasis on how these systems are to be powered.
The VITA 62 standard creates a set of design guidelines by which industry power supply vendors can build products that will be intermateable to VITA 62-compatible backplanes. OpenVPX currently only refines the power guidelines defined within VITA 46. It does not address any issues pertaining to powering such OpenVPX systems. When VITA 62 products are later defined in OpenVPX module, slot, and backplane profiles, they will allow system architects to specify power requirements for OpenVPX systems.
In addition to power conversion/conditioning, VITA 62 also defines secondary or utility slots for such system functions as inrush current, output control, Electro-Magnetic Interference (EMI), synchronization, and nuclear detection. VITA 62 has addressed and resolved many of these issues in the current draft, and some highlights of the accomplishments to date are described in the following sections.
Connectors and pins: Vital to VITA 62
VITA 62 leverages all the effort within the VITA 46, VITA 47 (environmentals), VITA 48 (VPX-REDI), and VITA 65 standards while providing a power-generation architecture that fully supports the needs of the critical-systems embedded community. Key to that goal is VITA 62’s new multivendor connector set for both 3U and 6U modules. The connectors fit into the current VITA 46 mechanical outline, thus facilitating the retrofitting of existing backplanes. The complete connector design, which facilitates efficient power conversion/conditioning, is included in the specification to support multiple connector companies’ implementations of VITA 62 connector sets. The connector reuses the same guide pins as defined in the ANSI/VITA 46.0 standard. The pins’ placement, also ANSI/VITA 46.0 compliant, eases modifications of the existing PWB designs to support VITA 62.
The VITA 62 power supply connector pin allocation was the main driving force in balancing the application’s needs versus availability of pins in these new connectors. The 3U posed the greatest challenge with its limited connector real estate. Figure 1 shows the current 3U connector set. These samples are being used at General Dynamics Canada to create a set of product offerings for VITA 62.
The VITA 62 pins’ definitions provide a good summary as to the design decisions that have been made in the selection of pins for VPX systems:
-DC_IN/CAN., +DC_IN/ACL CHASSIS,UD1,UD2, UD3,UD4,VBAT,FAIL*,INHIBIT*,ENABLE*,UD0, +12V_AUX,NED,NED_RETURN,3.3V_AUX,
VS3_SENSE, SENSE_RETURN, VS3, POWER_RETURN, POWER_RETURN, VS2, VS1
The VITA 62 committee decided to leverage the VITA 46 P0 utility connector pins to support requirements such as geographical addressing, system management, and other control functions while supporting maximum power generation. The connector supports both DC and AC input voltages, with three-phase AC supported only on the 6U connectors. The generation of a maximum 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 supports 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 modules attempt to fully power the components on the boards. This creates an initial current surge on the power supply, which, if not limited, could result in output rail voltages dropping below required levels. VITA 62 compliant systems will provide VPX module designers 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 compliant system will be able to correctly size the power requirements needed to be supported by the VITA 62 power module(s). This will eliminate potential system issues where VPX modules cannot 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 systems to support the use of an external on/off switch and the disabling of output rails.
EMI: Pertaining to EMI, VITA 62 provides 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 emission control, or to define requirements for external components.
Synchronization: Synchronizing power supplies is a recently discovered requirement for high-speed data acquisition systems. These systems typically need to synchronize data acquisition sampling times with power-supply switching times. VITA 62 allocates pins to allow 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 crowbar output rails on detections of an event. VITA 62 allows for both internal and external use of detection devices to support this capability.
Putting it all together
The existing VITA 46 key pins and keying definitions are used for VITA 62. This provides a means to identify up to five unique input powers. These keys will protect 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 keying pins. A single key on each connector defines the input voltage setting of the power supply. 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 connector 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.
Since all VITA 62 slots are connected in parallel, this allows secondary slots to add key system features without affecting primary slot functionality. A module designer could provide extra capability on a utility VITA 62 module, which, upon detection of loss of primary power, would “hold up” the inputs to the VITA 62 power supply for up to 50 ms or more. The VBAT pin can be used to maintain a low-power trickle charge to modules in the systems when main power is no longer available, thus allowing CMOS settings and “time of day” to remain active. The connection to the system management infrastructure provides the ability for a 46.11 shelf manager to reside in the VITA 62 utility slot.
What all this means
The diverse nature of the VITA 62 slot in system backplanes naturally lends itself to supporting important features that traditionally have been configured in a more ad hoc manner. And, VITA 62, once completed, will be integrated into the current OpenVPX standards by adding profiles for slots, modules, and backplanes, thus allowing system architects to fully design new VPX systems using a complete set of COTS modules. VITA 62 requires that the complete set of capabilities supported on the module be published by the vendors, so that system architect can then choose the module which best meets their needs. VITA 62 also solves the issues of managing inrush current, output control, EMI, synchronization, and nuclear detection. CS
General Dynamics Canada