CUSTOMIZED APPROACH which allow designers to make use of sophisticated, “undefined” features. These features are specification enhancements offered by some power supply manufacturers but not by others, even if they are VITA 62 compliant. A further complication is the programmability often offered with these power supplies, which is loosely defined in the VITA 46.11 system management specification. VITA 62 does define a starting point that system designers can use for basic power requirements. They must add actual power levels, as well as decide how to incorporate other undefined system power needs. EMI filtering and hold-up requirements, as well as transient and lightning protection, are just some of the possible considerations. If multiple cards are used, issues that must be resolved include shared circuit performance, compatibility, sensing, and synchronization. The VITA 62 specification, as currently released, allows for considerable flexibility in requirements. Output currents for each allowable voltage are the parameters that are most variable. Seldom does a power supply company see two requirements with the same output power levels. So it is important that products can be tailored to meet these needs. System integrators should not be afraid to ask for what is important, and power supply manufacturers must be able to discuss these needs and offer products that will meet them. Sometimes it might be important to stick with a fully compliant power supply, while other programs may allow some configuration changes in the interest of space savings or cost. An example is a system with a 5-V, 120-A requirement but which needs less power on the 12 and 3.3-V outputs. This type of situation is fairly common because some processor assemblies, widely used in VPX systems, need a significant amount of 5-V power. Standard 3U VPX cards come with outputs up to 5 V at 40 A because the pins designated for the 5-V output are rated at 40 A. One system designer may decide to meet the requirement using three cards and stay fully compliant with the VITA 62 specification. Another may opt for some tailoring of the card to reduce size and cost. The latter system designer may settle on using one standard card and a second card with two 5-V outputs by replacing the 12 V on that card with a second 5-V model. This approach would save a card slot, and it would cut the cost of the power supply roughly 33% because it used fewer cards. Each program designer must decide what degree of specification compliance or deviation they’ll accept. The designer should not be reluctant to discuss the requirement with the supplier; this interaction is usually the best way to optimize the design. In fact, it is important to consult with the power supply manufacturer early in the design stage because a reconfiguration of the power supply could affect other parts of the system design. The result could be added cost for reworking and more development time. Besides hardware requirements, VPX power supply software capability is also important for customizing and optimizing systems. Modern power supplies can be quite flexible. While IPMI-based VITA 46.11 can be used to optimize system performance, it doesn’t do much for defining programmable functions. Some manufacturers continue to use a PMBus-based I2C structure because the functions available are well defined. The specification for three-phase inputs on 3U cards. The current 3U connector does not have enough input pins to handle basic logic and control functions such as “card ready” or “fault.” powerelectronictips.com | designworldonline.com Behlman_P&EE9-16_V2.LT.indd 41 9 • 2016 Pin Number Rated Current (A) Pin Name P1 40A -DC_IN/ACN P2 40A +DC_IN/ACL LP1 20A CHASSIS A1 <1A UD1 B1 <1A UD2 C1 <1A UD3 D1 <1A UD4 A2 <1A VBAT B2 <1A FAIL* C2 <1A INHIBIT* D2 <1A ENABLE* A3 <1A UD0 B3 <1.5A +12V_AUX C3 <1A NED D3 <1A NED_RETURN A4 <1.5A 3.3V_AUX B4 <1.5A 3.3V_AUX C4 <1.5A 3.3V_AUX D4 <1.5A 3.3V_AUX A5 <1A GA0* B5 <1A GA1* C5 <1A SM0 D5 <1A SM1 A6 <1A SM2 B6 <1A SM3 C6 <1.5A -12V_AUX D6 <1A SYSRESET* A7 <1A PO1_SHARE B7 <1A PO2_SHARE C7 <1A PO3_SHARE D7 <1A SIGNAL_RETURN A8 <1A PO1_SENSE B8 <1A PO2_SENSE C8 <1A PO3_SENSE D8 <1A SENSE_RETURN P3 40A PO3 P4 40A POWER_RETURN P5 40A POWER_RETURN LP2 20A PO2 P6 40A PO1 DESIGN WORLD — EE Network 41 9/29/16 3:33 PM