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Fairchild RC5050 - page 1
Application Note 50 Implementing the RC5050 and RC5051 DC-DC Conver ters on Pentium ® Pr o Motherboar ds www .fair childsemi.com Intr oduction This document describes how to implement a switching v olt- age regulator using an RC5050 or an RC5051 high speed controller , a po wer inductor , a Schottky diode, appropriate capacitors, and external po w ...
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Fairchild RC5050 - page 2
AN50 APPLICATION NOTE 2 T able 2. Intel Pentium Pr o and OverDrive ® Processor P ower Specifications Notes: 1. Maximum power values are measured at typical V CC P to take into account the thermal time constant of the CPU package. 2. Flexible motherboard specifications are recommendations only. Actual specifications are subject to change. CPU Mode ...
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Fairchild RC5050 - page 3
APPLICATION NOTE AN50 3 I/O Controls In addition to the V oltage Identification, there are sev eral sig- nals that control the DC-DC con verter or provide feedback from the DC-DC con verter to the CPU. They are Po wer- Good (PWRGD), Output Enable (OUTEN), and Upgrade Present (UP#). These signals will be discussed later . RC5050 and RC5051 Descript ...
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Fairchild RC5050 - page 4
AN50 APPLICATION NOTE 4 The HIDR V driver has a po wer supply , VCCQP , supplied from a 12V source as illustrated in Figure 2. The resulting voltage is suf ficient to provide the gate to source voltage to the external MOSFET that is required to achie ve a low R DS,ON . Since the lo w side synchronous FET is referenced to ground, there is no need t ...
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Fairchild RC5050 - page 5
APPLICATION NOTE AN50 5 Short Circuit Protection A current sense methodology is implemented to disable the output driv e signal to the MOSFET(s) when an over-current condition is detected. The v oltage drop created by the output current flowing across a sense resistor is presented to an internal comparator . When the v oltage developed across the ...
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Fairchild RC5050 - page 6
AN50 APPLICATION NOTE 6 Figure 4. Synchronous DC-DC Converter Application Schematic Using the RC5051 VO GND VID3 VID2 VID1 VID0 8 7 6 5 4 3 2 1 9 10 11 12 13 14 15 16 17 18 19 20 +5V PWRGD RC5051 VCC ENABLE C10 0.1 µ F C11 0.1 µ F 10K C EXT C7 0.1 µ F C6 4.7 µ F DS1 1N5817 C1 1000 µ F C2 C3 1000 µ F 1000 µ F C5 0.1 µ F D1 1N4691 C12 1 µ F ...
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Fairchild RC5050 - page 7
APPLICATION NOTE AN50 7 MOSFET Selection Cosiderations MOSFET Selection This application requires N-channel Logic Lev el Enhance- ment Mode Field Effect Transistors. Desired characteristics are as follows: • Low Static Drain-Source On-Resistance, R DS,ON < 37 m Ω (lower is better) • Low g ate driv e voltage, V GS ≤ 4.5V • Power package ...
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Fairchild RC5050 - page 8
AN50 APPLICATION NOTE 8 T wo MOSFETs in parallel. W e recommend two MOSFETs used in parallel instead of one single MOSFET . The following significant adv antages are realized using two MOSFETs in parallel: • Significant reduction of P ower dissipation . Maximum current of 14A with one MOSFET : P MOSFET = (I 2 R DS,ON )(Duty Cycle) = (14) 2 (0.0 ...
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Fairchild RC5050 - page 9
APPLICATION NOTE AN50 9 Con ver ter Efficiency Losses due to parasitic resistance in the switches, coil, and sense resistor dominate at high load-current lev el. The major loss mechanisms under heavy loads, in usual order of impor - tance, are: • MOSFET I 2 R Losses • Coil Losses • Sense Resistor Losses • gate-charge losses • diode-condu ...
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Fairchild RC5050 - page 10
AN50 APPLICATION NOTE 10 Selecting the Inductor The inductor is one of the most critical components to be selected for a DC-DC con verter application. The critical parameters are inductance (L), maximum DC current (I O ), and DC coil resistance (R l ). The inductor core material is a crucial factor in determining the amount of current the inductor ...
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Fairchild RC5050 - page 11
APPLICATION NOTE AN50 11 Therefore, for load current of 14.5A, the peak current through the inductor , I pk , is found to be approximately 15.5A: Therefore, the short circuit detection threshold must be at least 16.5A. The next step is to determine the v alue of the sense resistor . Including sense resistor tolerance, the sense resistor value can b ...
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Fairchild RC5050 - page 12
AN50 APPLICATION NOTE 12 Embedded Sense Resistor (PC T race Resistor) Embedded PC trace resistors hav e the advantage of near zero cost implementation. Howe ver , the value of the PC trace resistor has large v ariations. Embedded resistors have 3 major error sources: the sheet resistivity of the inner layer , the mismatch due to L/W , and the tempe ...
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Fairchild RC5050 - page 13
APPLICATION NOTE AN50 13 tion. The embedded sense resistor allows the user to choose a plus or a minus delta resistance tap to offset an y large sheet resisti vity change. In this design, the center tap yields 6m Ω , the left tap yields 6.7m Ω , and the right tap yields 5.3m Ω . RC5050 and RC5051 Short Circuit Current Characteristics The RC50 ...
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Fairchild RC5050 - page 14
AN50 APPLICATION NOTE 14 Figure 13A. V CCQP Output Waveform for Normal Operation Condition with V out = 3.3V@10A Figure 13B. V CCQP Output Waveform for Output Shorted to Ground Power dissipation on the Schottk y diode during a short cir- cuit condition must also be considered. During normal oper- ation, the Schottky diode dissipates po wer while th ...
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Fairchild RC5050 - page 15
APPLICATION NOTE AN50 15 FET . Low Equi valent Series Resistance (ESR) capacitors are best suited for this type of application. Incorrect selection can hinder the con verter's overall performance. The input capacitor should be placed as close to the drain of the FET as possible to reduce the effect of ringing caused by long trace lengths. The ...
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Fairchild RC5050 - page 16
AN50 APPLICATION NOTE 16 PCB La yout Guidelines and Considerations PCB Lay out Guidelines • Placement of the MOSFETs relativ e to the RC5050 is critical. Place the MOSFETs (M1 & M2) so that the trace length of the HIDR V pin from the RC5050 to the FET gates is minimized. A long lead length on this pin would cause high amounts of ringing due t ...
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Fairchild RC5050 - page 17
APPLICATION NOTE AN50 17 In general, all of the noisy switching lines should be kept aw ay from the quiet analog section of the RC5050. That is, traces that connect to pins 12 and 13 (HIDR V and VCCQP) should be kept far a way from the traces that con- nect to pins 1 through 5, and pin 16. • Place the 0.1 µ F decoupling capacitors as close to th ...
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Fairchild RC5050 - page 18
AN50 APPLICATION NOTE 18 Guidelines f or Debug ging and P erformance Ev aluations Debug ging Y our First Design Implementation 1. Note the setting of the VID pins to kno w what voltage is to be expected. 2. Do not connect any load to the circuit. While monitoring the output voltage, apply po wer to the part with current limiting at the power supply ...
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Fairchild RC5050 - page 19
APPLICATION NOTE AN50 19 Note: Load regulation is expected to be typically around 0.8%. The load regulation performance for this device under evaluation is excellent. Output V oltag e Load T ransients Due to Load Current Step This test is performed using Intel P6.0/P6S/P6T V oltage T ransient T ester . Note: Transient voltage is recommended to be l ...
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Fairchild RC5050 - page 20
AN50 APPLICATION NOTE 20 Input Ripple and P ower on Input Rush Current Note: Excellent input ripple voltage. Input ripple voltage is recom- mended to be less than 5% of the output voltage. Po wer on Input Rush Current w as 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 sup ...
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Fairchild RC5050 - page 21
APPLICATION NOTE AN50 21 Attachment C Attachment D Attachment E Attachment F Attachment G ...
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Fairchild RC5050 - page 22
AN50 APPLICATION NOTE 22 Summary This application note cov ers many aspects of the RC5050 and RC5051 for implementation of a DC-DC con verter a on Pentium Pro motherboard. A detailed discussion includes the processor power requirements, a description of the RC5050 and RC5051, design considerations and compo- nents selection, layout guidelines and c ...
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Fairchild RC5050 - page 23
APPLICATION NOTE AN50 23 Appendix A Directory of Component Suppliers Dale Electronics, Inc. E. Hwy . 50, PO Box 180 Y ankton, SD 57078-0180 PH: (605) 665-9301 Fuji Electric Collmer Semiconductor Inc. 14368 Proton Rd. Dallas, T exas 75244 PH: (214)233-1589 General Instrument Power Semiconductor Di vision 10 Melville Park Road Melville, NY 11747 PH: ...
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Fairchild RC5050 - page 24
AN50 APPLICATION NOTE 2/98 0.0m Stock#AN30000050 1998 Fairchild Semiconductor Corporation LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support de ...
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