Fairchild RC5040 specifications Introduction, Input Voltages, Pentium Pro DC Power Requirements

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Application Note 42

Implementing the RC5040 and RC5042

DC-DC Converters on Pentium® Pro Motherboards

Introduction

This document describes how to implement a switching volt- age regulator using an RC5040 or an RC5042 high speed controller, a power inductor, a Schottky diode, appropriate capacitors, and external power MOSFETs. This regulator forms a step down DC-DC converter that can deliver up to 14.5A of continuous load current at voltages ranging from 2.1V to 3.5V. A specific application circuit, design consider- ations, component selection, PCB layout guidelines and per- formance evaluation procedures are covered in detail.

Pentium Pro and OverDrive® Processor Power Requirements

Use Intel’s AP-523 Application Note, Pentium® Pro Processor Power Distribution Guidelines, November 1995 (order number 242764-001), as a basic reference. The speci- fications contained in this document have been modified slightly from the original Intel document to include updated specifications for Pentium Pro microprocessors. Please con- tact Intel Corporation for specific details.

In the past 10 years, microprocessors have evolved at such an exponential rate that a modern chip can rival the computing power of a mainframe computer. Such evolution has been possible because of the increasing numbers of transistors that processors integrate. Pentium CPUs, for example, integrate well over 5 million transistors on a single piece of silicon.

To integrate so many transistors on a piece of silicon, their physical geometry has been reduced to the sub-micron level. As a result of each geometry reduction, the corresponding operational voltage for each transistor has also been reduced. This changing voltage for the CPU demands the design of a programmable power supply—a design that is not com- pletely re-engineered with every change in CPU voltage.

The operational voltage of CPUs has shown a downwards trend for the past 5 years: from 5V for the x386 and x486, to 3.3V for Pentium, and 3.1V for Pentium Pro. Furthermore, emerging chip technologies may require operating voltages as low as 2.5V. With this trend in mind, Raytheon Electron- ics has designed the RC5040 and RC5042 controllers. These controllers integrate the necessary programmability to address the changing power supply requirements of lower voltage CPUs.

Previous generations of DC-DC converter controllers were designed with fixed output voltages adjustable only with a set of external resistors. In a high volume production envi- ronment (such as with personal computers), however, a CPU voltage change requires a CPU board re-design to accommo- date the new voltage requirement. The integrated 4-bit DAC in the RC5040 and the RC5042 reads the voltage ID code from the Pentium Pro microprocessor and configures the sys- tem to provide the appropriate voltage. In this manner, the PC board does not have to be re-designed each time the CPU voltage changes. The CPU can thus automatically configure its own required voltage.

Input Voltages

Available inputs are +5V ±5% and +12V ±5%. Raytheon Electronics’ DC-DC converters may use either or both inputs. Their input voltage requirements are listed in Table 1.

Table 1. Input Voltage Requirements

 

Controller

MOSFET

MOSFET

Part #

VCC

Drain

Gate Bias

 

 

 

 

RC5040

+5V ±5%

+5V ±5%

+5V ±5% or

RC5042

 

 

12V ±5%

 

 

 

 

RC5043

+5V ±5%

12V ±5%

12V ±5%

 

 

 

 

Pentium Pro DC Power Requirements

Refer to Table 2 for the power supply specifications for Pentium Pro and Overdrive Processors. For a motherboard design without a standard Voltage Regulator Module (VRM) socket, the on-board DC-DC converter must supply a mini- mum ICCP current of 13.9A at 2.5V and 12.4A at 3.3V. For a flexible motherboard design, the on-board converter must be able to supply 14.5A maximum ICCP.

DC Voltage Regulation

As indicated in Table 2, the voltage level supplied to the CPU must be within ±5% of its nominal setting. Voltage regulation limits must include:

•Output load ranges specified in Table 2

•Output ripple/noise

•DC output initial voltage set point

•Temperature and warm up drift (Ambient +10°C to +60°C at full load with a maximum rate of change of 5°C per 10 minutes minimum but no more than 10°C per hour)

•Output load transient with:

Slew rate >30A/∝s at the converter pins

Range: 0.3A – ICCP Max (as defined in Table 2).

Rev. 1.1.0

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Contents Introduction Pentium Pro DC Power RequirementsInput Voltages DC Voltage RegulationEfficiency Output Ripple and NoiseProcessor Voltage Identification ControlsSimple Step-Down Converter RC5040 and RC5042 DescriptionRC5040 and RC5042 Controllers Output Enable Outen Power Good PwrgdUpgrade Present UP# Main Control LoopOver-Voltage Protection Design Considerations and Component SelectionShort Circuit Protection OscillatorRC5042 Two MOSFETs in Parallel Mosfet SelectionThermal Conditions1 Manufacturer & Model # Typ MaxMosfet Gate Bias Charge Pump or BootstrapConverter Efficiency Implementing Short Circuit Protection Selecting the InductorShort Circuit Comparator Description Discrete MetalResistor IRC Resistor= 2000mi Resistor mΩFor each Mosfet RC5040 and RC5042 Short Circuit Current Characteristics⋅ .2 = 0.74W Schottky Diode Selection Output Filter Capacitors Schottky Diode Selection TableInput filter Bill of MaterialsPCB Layout Guidelines PCB Layout Guidelines and ConsiderationsMotorola Shottky Diode 320-6110PC Motherboard Layout and Gerber File Example of Proper MOSFETs PlacementsApplication Note Guidelines for Debugging and Performance Evaluations TroubleshootingDebugging Your First Design Implementation Vout Performance Evaluation+ 80.0mV Iload =13.9A Device DescriptionRC5040/RC5042 Evaluation Board SummaryLife Support Policy Appendix a Directory of Component Suppliers

RC5040, RC5042 specifications

The Fairchild RC5042 and RC5040 are versatile integrated circuits that stand out in the realm of high-performance analog applications. Designed to meet the demands of modern electronic systems, these devices integrate various features and technologies that contribute to their effectiveness in a multitude of applications.

The RC5040 is a precision voltage reference that offers a stable, low-noise output, making it ideal for applications such as instrumentation, data acquisition systems, and RF circuits. It boasts an operating temperature range of -40°C to +85°C, ensuring reliability in diverse environments. One of its most significant characteristics is its low-temperature drift, which minimizes variations in output voltage over temperature fluctuations, thereby enhancing the accuracy of devices that utilize it.

On the other hand, the RC5042 is designed as a high-speed comparator with an integrated voltage reference. This dual functionality allows for a more compact design in applications where space is a premium. The RC5042 features an ultra-fast response time and high input impedance, which contribute to its capability to handle rapidly changing signals without distortion. This makes it particularly useful in applications like analog signal processing and threshold detection.

Both devices utilize Fairchild's advanced BiCMOS technology, which combines the benefits of bipolar and CMOS processes. This technology allows the devices to operate with low power consumption while maintaining high speed and operational efficiency. The RC5042 and RC5040 also incorporate noise-reduction techniques, which help in minimizing unwanted disturbances that could impact circuit performance.

Another noteworthy characteristic of both the RC5040 and RC5042 is their ease of integration. They come in compact package sizes, making them easier to incorporate into various designs without compromising on performance. Furthermore, the availability of multiple output options allows engineers the flexibility to choose configurations that best suit their specific applications.

In conclusion, the Fairchild RC5042 and RC5040 are robust devices that offer essential functionality for various high-performance analog applications. With their precision, fast response time, and exceptional reliability, these integrated circuits are a valuable asset in the design of modern electronic systems, catering to the growing demands of the technology landscape.
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