Fairchild RC5050, RC5051 Evaluation Summary

AN50 APPLICATION NOTE

20

Input Ripple and Power on Input Rush Current

Note:

Excellent input ripple voltage. Input ripple voltage is recom-

mended to be less than 5% of the output voltage.

Power on Input Rush Current was not measured on the moth-

erboard because we did not want to cut the 5V trace and

insert a current probe in series with the supply. However,

with the input ﬁlter design, the Input Rush Current is well

within speciﬁcation.

Iload = 9.9A Input Ripple

Voltage = 15mV Refer to Attach-

ment G for Scope

Picture

Component Case Temperature

Note:

The values for case temperatures are within guidelines. That is, case temperatures for all components should be below

105°C @25°C Ambient.

Device Description

Case Temperature

Iload = 9.9A

(°C)

Case Temperature

Iload = 12.4A

(°C)

Case Temperature

Iload = 13.9A

(°C)

Q3A MOSFET

K1388 57 63 66.3

Q3B MOSFET

K1388 58 64 66.6

L1 Inductor,

Unknown 53 56 61.2

Q2 Schottky Diode

2048CT 66 70 87

IC Raytheon’s RC5050 52 54 58

Cin Input Cap. 1000µF 38.2 36.8 39

Cout Output Cap.

1500µF35 34.8 38.2

Evaluation Summary

The on-board DC-DC converter is fully functional. It has

excellent load regulation, transient response, and input volt-

age ripple.

Attachment A Attachment B

Contents

Main Application Note 50 Implementing the RC5050 and RC5051 DC-DC Converters on Pentium Pro Motherboards www.fairchildsemi.com Introduction Table 2. Intel Pentium Pro and OverDrive Processor Power Specications Output Ripple and Noise Efciency Processor Voltage Identication Table 3. Output Voltage Programming Codes RC5050 and RC5051 Description Simple Step-Down Converter The RC5050 and RC5051 Controllers Table 4. RC5050 and RC5051 Differences Main Control Loop Internal Voltage Reference Power Good (PWRGD) Output Enable (OUTEN) Upgrade Present (UP#) Over-Voltage Protection Design Considerations and Component Selection AN50 APPLICATION NOTE Figure 4. Synchronous DC-DC Converter Application Schematic Using the RC5051 RC5051 MOSFET Selection Cosiderations Table 3. MOSFET Selection Table Page Converter Efciency Selecting the Inductor Implementing Short Circuit Protection Table 6. RC5050 Short Circuit Comparator Threshold Voltage Table 7. Comparison of Sense Resistors Table 8. Rsense for Various Load Currents Table 9. Summary PC Trace Resistor Tolerance RC5050 and RC5051 Short Circuit Current Characteristics Power Dissipation Consideration During a Short Circuit Condition Schottky Diode Selection Table 10. Schottky Diode Selection Table Output Filter Capacitors Input Filter Bill of Material Table 11. Bill of Materials for a 13A Pentium Pro Klamath Application PCB Layout Guidelines and Considerations PCB Layout Guidelines Table 11. Bill of Materials for a 13A Pentium Pr o Klamath Application Example of a PC Motherboard Layout and Gerber File. Guidelines for Debugging and Performance Evaluations Debugging Your First Design Implementation Procedures Performance Evaluation Page Evaluation Summary Page Summary RC5050 Evaluation Board Appendix A Directory of Component Suppliers