VITA 62 Power Supplies: Filling a Standards Gap for 3U VPX Systems



The recently ratified VITA 62 standard provides clear definitions for power supply vendors and supports a powerful set of advanced features, making the mission-critical system designer’s job immensely easier.

In today’s defense electronics environment, systems designers rely on open standards to help them deal with both compressed development schedules and the expectation of frequent technology upgrades.  This is especially true for systems targeting smaller platforms where time to deployment can be sandwiched into a one year window.  The 3U VPX board-level standard has evolved to fill this need.

However, while the embedded systems community has embraced board-level open standards for processing modules, mezzanine cards, I/O protocols and backplane connections, power supplies have continued to be addressed in an ad hoc manner, without the guidance of an accepted standard.  The recently ratified VITA 62 standard was developed to address this gap.

As an accepted industry standard, VITA 62 promotes competition, reduces costs and advances technology with ready to deploy COTS (commercial off the shelf) power supply modules, allowing developers to rapidly integrate reliable power into VPX system designs.

A comprehensive power supply standard
The VITA 62 power supply standard supports interoperability, configuration flexibility, advanced levels of reliability and sophisticated systems management.  It ensures that power supply electrical and mechanical standards are compatible with the popular VPX system platform and assures that any standard-compliant power supply can be interchanged with any other, will fit mechanically into the same chassis and will meet the same electrical standards.

In scope, the standard defines a connector configuration, power generation requirements, and utility, functionality and form factor requirements for power supply modules mating to a VPX backplane.  At a detailed level, VITA 62 specifies power supply input and output voltages and currents, pin-outs, slot size, and mechanical configurations for VPX systems, and allocates specific pins for multiple power supply load sharing capability.  The VITA 62 connector is specified so as to withstand frequent reconnect cycles, while the slot and mechanical sizes and tolerances are defined to achieve the tight fit required for efficient conduction cooling.

The VITA 62 3U pin out specifies power and signal connections. There are also User Defined (UD) pins allotted for application-specific tasks (marked as OPT(x) in Figure 1), blades and receptacles and pins provided for power in and out.

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Figure 1: VITA 62 compliant connector pin out (card view). Note the voltage options for 12V, 3.3V and 5V (PO1-PO3) along with the User Defined (UD) pins.

This figure shows the VITA 62 3U compliant connector pinout (card view). UD (User Defined) pins are available for optional, application specific purposes. Power blade and receptacles are provided for power supply outputs PO1 +12V, PO2 +3.3V and PO3 +5V. These voltages are also provided on pins as auxiliary outputs. VBAT is provided for memory back-up battery.

VITA 62 also exploits the effectiveness of interlocking standards, referencing definitions that already exist and are widely used.  It supports VITA 46.11 IPMB (Intelligent Platform Management Bus), VITA 48 REDI (Ruggedized Enhanced Design Implementation) and provides guidelines for adherence to MIL-STD-461F (electromagnetic interference), MIL-STD-704F (electrical standards and holdup time) and MIL-STD-810F (mission critical ruggedization) compliance.

Interlocking With Electrical And Harsh Environment Standards
VITA 62 supports MIL-STD-704F which sets electrical standards for military aircraft such as AC voltage power factor, harmonics, distortion spectrum and load balance currents, DC voltage, currents, ripple, transients, ground configuration and the crucial to mission critical deployment holdup time, which allocates for power on "meltdown."  Chassis, electrical and power supply return must be separate to one point.   

Also supported is VITA 48 REDI (Ruggedized Enhanced Design Implementation).   Part of VITA 48 has a defined pitch –the interval on a backplane of each module–of 1.0”.  This is an increase over the 0.8” pitch of the older VME standard, a change which permits higher power levels and taller components.  In addition, air, liquid, and conduction cooling parameters are defined within VITA 48 to provide uniform packaging alignment.

Although all semiconductor devices are subject to damage by ionizing radiation, high density semiconductors are the easiest to be damaged by ionizing radiation. A NED (Nuclear Event Detect) input is supported by VITA 62 to shut down power during such an event.

SENSE pins permit feedback of +12V, +5V and +3.3V to the power supply. These voltages compensate for IR (current-resistance) drop at the connection and provide correction to some of the transients produced by load surges. SHARE pins facilitate current balancing between power supplies operated in parallel. The VBAT pin permits an on board battery to supply power to system non-volatile memory. This is important to save system CMOS settings and other low power volatile storage.

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Figure 2: Typical VITA 62 3U electrical configuration

This block diagram shows VITA 62 3U power supply electrical connections. VS1, VS2 and VS3 show DC outputs +12V, +3.3V and +5V respectively. Current sharing signals represented by the SHARE signals are sent between power supplies in a sharing configuration. SENSE lines feedback signals to regulate power output voltages VS1, VS2 and VS3 to the remote load. VITA 46.11 Bus is the I2C link to the Chassis Manager. The NED input indicates the presence of Nuclear Event. ACL and ACN are AC line (hot) and neutral.

Intelligent Platform Management Bus support
VITA 46.11 IPMB (Intelligent Platform Management Bus) is focused on ensuring reliable systems operation and is referenced in VITA 62.  VITA 46.11 specifies that an I2C serial bus be used for communication between modules and the Intelligent Chassis Manager. This link facilitates sophisticated systems management through onboard processor control and monitoring. Monitoring on board sensors permits an Error Log to be created that flags conditions that may have contributed to failure.

Conditions in the field can never fully be anticipated by any test since an unusual set of circumstances may act together to cause system failure. The Error Log produced by the Intelligent Chassis Manager is thus extremely important because it documents conditions in the field that led to failure. It is important that the cause of failure be identified for future maintenance and design. The design engineer must be fully aware of events leading to failure. This is where the Error Log is important, it keeps a log of critical parameters such as vibration, humidity, and temperature.

For example, the Error Log may indicate that a particular board has a problem with temperature caused by cooling fans. The System Manager can then be programmed to lower the fan speed so that the temperature of the board is just below its upper specification.

Critical Vita 62 Power Supply Characteristics
VITA 62 power supplies have unique challenges in modern deployment systems. Smart VITA 62 power supplies have voltage rail control which enables them to be individually sequenced, up and down. This provides critical sequencing to CPU cards, FPGA cards and other VITA 65 cards, which are sensitive to which voltage comes up first.

Power sharing between two or more supplies can be advantageous if total current requirements exceed that which can be delivered by a single supply. It can also be advantageous if there is at least one supply more than that required. Referred to as N+1 redundancy, if one power supply fails the system can still supply the required current using the remaining functional supplies. It also means that power supplies can be hot swapped. In addition, N+1 redundancy reduces the power dissipated by each supply and reduced power means a lower onboard temperature.

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Figure 3: Examples of 3U VITA 62-compliant power supplies from Dawn VME Products. The PSC-6236 air-cooled design on the left includes a front panel with connections, while the equivalent conduction-cooled LRU on the right clearly shows wedgelocks for cold plate cooling. These compact PSUs can source 400 W over a wide temperature range.

Paralleling power supplies requires that the output current of each power supply’s voltage rail be balanced. This is a task accomplished by a SHARE reference signal. An analog reference signal for each of the voltage rails is connected between each of the system power supplies through the appropriate SHARE pin.

VITA 62 compliant solutions
The first implementations of VITA 62 compliant solutions are now appearing on the market.  An example is shown in Figure 3, the Dawn PSC-6236 Universal AC Input VITA 62 3U Power Supply for air or conduction cooled systems.  Designed for mission critical applications, it delivers up to 400 Watts of output power over a wide temperature range.

New products like this represent a standardized power supply ready to deliver in harsh mission critical environments.
A short summary of the benefits includes:

  • Simplified systems designs due to clear, standards-based definitions
  • Interoperability increasing competition and driving down costs
  • Support for interlocking electrical and harsh environment standards
  • Error logs to facilitate rapid diagnosis of problems
  • Power sharing and N+1 redundancy driving increased reliability and maintainability.
  • Provides critical voltage sequencing to system cards.

 


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Brian Roberts has 22 years of design experience in Silicon Valley developing electronic products for commercial and defense applications. Over this period, he has worked with clients in the areas of system engineering, power supply design, and other printed circuit board based solutions. Brian has been with the team at Dawn VME Products since 2005.

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