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Fairchild Summary, RC5040/RC5042 Evaluation Board, Attachment C, Attachment E, Attachment D

Models: RC5040 RC5042

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APPLICATION NOTE	AN42

Attachment C

Attachment E

Attachment D

Attachment F

Attachment G

Summary

This application note covers for implementation of a DC-DC converter on a Pentium Pro motherboard using the RC5040 and RC5042. The detailed discussion includes Pentium Pro processor power requirements, RC5040 and RC5042 description, design considerationsn and component selec- tions, layout guidelines and considerations, guidelines for debugging, and performance evaluations.

RC5040/RC5042 Evaluation Board

Raytheon Electronics provides an evaluation board for the purpose of verifying system level performance of the RC5040 and RC5042. The evaluation board serves as a guide as to what can be expected in performance with the supplied external components and PCB layout. Please call Raytheon Electronics Marketing Department at (415) 966-7819 for an evaluation board.

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Fairchild Summary, RC5040/RC5042 Evaluation Board, Attachment C, Attachment E, Attachment D, Attachment F, Attachment G

Contents

DC Voltage Regulation Pentium Pro DC Power RequirementsIntroduction Input VoltagesI/O Controls Output Ripple and NoiseEfﬁciency Processor Voltage IdentiﬁcationSimple Step-Down Converter Output EnableDisable RC5040 and RC5042 DescriptionMain Control Loop Power Good PWRGDOutput Enable OUTEN Upgrade Present UP#Oscillator Design Considerations and Component SelectionOver-Voltage Protection Short Circuit ProtectionRC5042 Conditions1 MOSFET SelectionTwo MOSFETs in Parallel ThermalFigure 7. 12V Gate Bias Configuration MOSFET Gate BiasCharge Pump or Bootstrap Figure 6. Charge Pump ConfigurationExample Converter EfﬁciencyDesign Equations Short Circuit Comparator Selecting the InductorImplementing Short Circuit Protection Resistor IRC Discrete MetalDiscrete DescriptionThermal Considerations Resistor mΩSheet resistivity Mismatch due to L/WOutput RC5040 and RC5042 Short Circuit Current CharacteristicsPower Dissipation Consideration During a Short Circuit Condition Output Current Figure 13. RC5040/RC5042 Short Circuit CharacteristicSchottky Diode Selection Bill of Materials Table 10. Schottky Diode Selection TableOutput Filter Capacitors Input ﬁlterOptional - will help re PCB Layout Guidelines and ConsiderationsPCB Layout Guidelines Vf0.72V @ If = 15A= “Quiet” Pins PC Motherboard Layout and Gerber FileAPPLICATION NOTE AN42Debugging Your First Design Implementation TroubleshootingGuidelines for Debugging and Performance Evaluations Vout Performance EvaluationVout Output Voltage Load Transients Due to Load Current Step Input Ripple and Power on Input Rush CurrentVout Iload ADescription DeviceIload =13.9A Component Case TemperatureAttachment E SummaryRC5040/RC5042 Evaluation Board Attachment CLIFE SUPPORT POLICY Appendix A Directory of Component Suppliers