AN42

APPLICATION NOTE

 

 

4.Premature shut down can be caused by an inappropriate value of sense resistor. See the Sense Resistor section.

5.A poor load regulation can have many causes. You should first check the voltages and signals at the critical pins.

6.The VREF pin should be at the voltage set by the VID pins. If the power supply pins are correct and the VID pins are correct, the VREF should be at the correct volt- age.

7.Next check the oscillator pin. A saw tooth wave at the frequency set by the external capacitor should be seen.

8.When the VREF and CEXT pins are determined to be correct and the output voltage is still incorrect look at the waveform at VCCQP. This pin should be swinging from ground to +12V (in the +12V application) and from slightly below +5V to about +10V (charge pump application). If the VCCQP pin is noisy, with ripples and overshoots, then the noise may cause the converter to function improperly.

9.Next, look at the HIDRV pin. This pin directly drives the gate of the FET. It should provide a gate drive (Vgs) of about 5V when turning the FET on. A careful study of the layout is recommended. See the PCB Layout Guide- lines and Considerations section.

10.Experience shows that the most frequent errors are using incorrect components, improper connections, and poor layout.

Performance Evaluation

This section shows the results of a random sample evalua- tion. Use these results as a reference guide for evaluating the RC5040 DC-DC converter for Pentium Pro motherboards.

Load Regulation

VID

Iload (A)

Vout (V)

0100

0.5

3.0904

 

 

 

 

1.0

3.0825

 

 

 

 

2.0

3.0786

 

 

 

 

3.0

3.0730

 

 

 

 

4.0

3.0695

 

 

 

 

5.0

3.0693

 

 

 

 

6.0

3.0695

 

 

 

 

7.0

3.0695

 

 

 

 

8.0

3.0694

 

 

 

 

9.0

3.0694

 

 

 

 

9.9

3.0691

 

 

 

Load Regulation 0.5A – 9.9A

0.70%

 

 

 

 

 

 

VID

Iload (A)

Vout (V)

0010

0.5

3.2805

 

 

 

 

1.0

3.2741

 

 

 

 

2.0

3.2701

 

 

 

 

3.0

3.2642

 

 

 

 

4.0

3.2595

 

 

 

 

5.0

3.2597

 

 

 

 

6.0

3.2606

 

 

 

 

7.0

3.2611

 

 

 

 

8.0

3.2613

 

 

 

 

9.0

3.2611

 

 

 

 

10.0

3.2607

 

 

 

 

11.0

3.2599

 

 

 

 

12.0

3.2596

 

 

 

 

12.4

3.2596

 

 

 

Load Regulation 0.5A – 12.4A

0.64%

 

 

 

20

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Fairchild RC5042, RC5040 specifications Performance Evaluation, Vout

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.