By Gino F. Nanninga
 Figure 1. PICMG 2.11 power connectors. |
The PICMG 2.11 Power Interface Specification details mechanical and electrical requirements for pluggable power supplies that are used in CompactPCI systems.
As computing systems continue to grow, so does the demand for the power to drive them. This increasing demand is because of the availability of more computing capability in a given space. Also, reductions in the voltages that are required to drive modern electronic devices have caused a shift in the power mix. These factors will continue to contribute to the need for higher density power supplies into the future. This is particularly true when the system design calls for power supplies to be placed into the subrack, which serves to displace system features.
Power Supply Challenges
Higher power density is only one of the challenges that power supply manufacturers face. Other features add to the complexity of power supply design, such as:
- Hot-swap capability
- Communication with the host system
- Redundancy
- Regulation of bus voltages
- Cooling considerations
 Various power connector options. |
In addition, reduced price, greater availability and time-tested quality are important to power supply users. Although individual manufacturers shoulder much of the responsibility for price, availability and quality, power supply standardization can aid in this effort.
The October 2000 edition of Connector Specifier contained an article entitled, "The Past, Present, and Future of Power Connectors," by Tom Johnson. The author did a thorough job of outlining the evolution of power connectors. However, one segment of the article, Power Interface Specifications, requires a more detailed analysis. This specification was developed to provide standard power solutions for CompactPCI systems.
In April of 1998, the PCI Industrial Computer Manufacturers Group (PICMG) 2.11 Power Interface Specification Subcommittee was charged with the task of developing a new specification. The subcommittee members represented a consortium of industry experts from more than 20 companies. The goal of the subcommittee was to develop a power supply specification that would provide for the power needs and feature requirements of today's systems, while allowing for a growth path into the future.
Specification Features
On October 1, 1999, the PICMG 2.11 R1.0 Power Interface Specification was adopted. This specification details in-rack power supplies for CompactPCI applications and includes these features:
- Standardized form factor and connector interface, which details placement of power supplies within the subrack along with the location of the power interface
- Multivoltage output of up to 600 W with a single connector
- Standardized electrical interface (see Table 1)
- Alternating current (AC) or direct current (DC) power input
- Keying for input and output power configurations
- Regulation of bus voltages to ensure compliance with CompactPCI requirements
- Hot-swap capability
- Communication with the host system
- 3U and 6U options
- Compliance to common international safety requirements
In addition, the PICMG 2.11 specification provides some guidance for common performance requirements that may be applicable in certain situations, such as when network equipment building system (NEBS) requirements are a consideration in telecommunications applications. Other requirements can be included as the need arises.
Although the PICMG 2.11 specification creates certain mechanical and electrical parameters for pluggable power supplies, the innovation of individual manufacturers is preserved. This encourages solutions for a variety of general system requirements at the best performance-to-cost ratios for a specific system. The specification allows for independent design regarding:
- Power factor correction
- Filtering
- Current sharing
- Cooling characteristics
Power Connecter Interface
The PICMG 2.11 specification details a 47-contact power connector with three input, 24 signal and 20 output contacts (see Figure 1). The connector is 3.7" (93.82 mm) long and 0.5" (12.54 mm) high. It was specifically designed so that a single connector could be used in 3U and 6U power supplies that are capable of delivering up to 600 W.
The October 2000 article supports the PICMG 2.11 power connector for use in low-to-midrange power applications, but questions whether or not it will address the "higher end" of the power spectrum. A power connector referred to in that article has blade-style contacts and is configured with three input, 24 signal and nine output contacts. The article states that this connector can provide higher levels of performance compared to the PICMG 2.11 power connector, but is this possible?
Table 2 shows certain characteristics of the PICMG 2.11 power connector. If the PICMG 2.11 interface was compared to a connector with larger power contacts, it is reasonable to speculate that such a connector would have eight output contacts. This is because an even number is required to maintain a balance between contacts that support voltages and associated returns, assuming all contacts are under continuous load. Ten large output contacts are not likely to fit into the package without displacing other features.
The total output current of the PICMG 2.11 power connector (using Underwriters Laboratories' [UL] ratings) is 560 A through 20 contacts. A connector with eight larger power contacts would require a UL rating of at least 70 A per contact in order to match this output capability.
Also of interest is the fact that the PICMG 2.11 specification provides for multivoltage output (see Table 1). The 20 output contacts of the PICMG 2.11 power connector provide for efficient distribution of current between multivoltages. For example, two contacts may be sufficient for a 12 V output and return because higher voltages require less current. This allows the other 18 contacts of the connector to be divided in various ways among other output voltages.
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If another type of power connector with larger but fewer contacts (assuming equal package size) is used, a single contact is still required for +12 V. If the 12 V current requirement is, for example, only 16 A, much of the larger contact's current capability is underutilized, and thus, the current-carrying capability of the connector is inefficiently distributed between multivoltages.
Conclusion
All requirements for power connectors do not revolve around one type of connector, and no one connector can meet all needs. The demand is increasing for a broad range of contact variants, package sizes, geometries and termination types.
Features such as sequential and blind mating and hot-swap capability are also essential. Engineers will continue to seek a variety of power connector options that allow for unique solutions in today's complex designs.
GINO F. NANNINGA is Vice President of Sales, Positronic Industries Inc., 423 N. Campbell, Springfield, MO 65801; (417) 866-2322; Fax: (417) 866-4115; E-mail: gnanninga@positronic.com; Web site: www.positronic.com. Mr. Nanninga has also served as Chairman of the PICMG 2.11 Power Interface Subcommittee. For more information, visit www.picmg.com.
SPEC SHEET
End Applications:
CompactPCI systems
Related Products:
Power connectors, power supplies
Main Point:
The PICMG 2.11 Power Interface Specification was developed to provide standard power solutions for CompactPCI systems. The PICMG 2.11 specification details a 47-contact power connector with three input, 24 signal and 20 output contacts. The connector was specifically designed so that a single connector could be used in 3U and 6U power supplies that are capable of delivering up to 600 W. This solution provides engineers with a power connector option for today's complex, high-powered designs.
