Fairchild RC5040, RC5042 specifications Mosfet Selection, Two MOSFETs in Parallel, Thermal

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APPLICATION NOTE

AN42

 

 

MOSFET Selection

This application requires the use of N-channel, Logic Level Enhancement Mode Field Effect Transistors. The desired characteristics of these components are:

•Low Static Drain-Source On-Resistance RDS,ON < 37 mΩ (lower is better)

•Low gate drive voltage, VGS ≤ 4.5V

•Power package with low thermal resistance

•Drain current rating of 20A minimum

•Drain-Source voltage > 15V.

The on-resistance (RDS,ON) is the main parameter for MOS- FET selection. It determines the MOSFET’s power dissipa- tion, thus significantly affecting the efficiency of the converter. Several suitable MOSFETs are shown in Table 5.

Table 5. MOSFET Selection Table

 

 

 

RDS,ON(mΩ)

 

Thermal

 

Conditions1

 

 

 

Manufacturer & Model #

Typ.

Max.

Package

Resistance

Fuji

VGS = 4V

TJ = 25°C

25

37

TO-220

ΦJA = 75

2SK1388

ID = 17.5A

 

 

 

 

 

TJ = 125°C

37

—

 

 

 

 

 

 

 

 

 

 

 

 

 

Siliconix

VGS = 4.5V

TJ = 25°C

16.5

20

SO-8

ΦJA = 50

SI4410DY

ID = 5A

 

 

 

(SMD)

 

TJ = 125°C

28

34

 

 

 

 

 

 

 

 

 

 

 

 

National Semiconductor

VGS = 5V

TJ = 25°C

13

15

TO-220

ΦJA = 62.5

NDP706AL

ID = 40A

 

 

 

 

ΦJC = 1.5

 

 

 

 

 

 

 

NDP706AEL

 

TJ = 125°C

20

24

 

 

 

 

 

 

 

 

 

National Semiconductor

VGS = 4.5V

TJ = 25°C

31

40

TO-220

ΦJA = 62.5

 

ID = 10A

 

 

 

 

 

NDP603AL

TJ = 125°C

42

54

 

ΦJC = 2.5

 

 

 

 

 

 

 

 

 

National Semiconductor

VGS = 5V

TJ = 25°C

22

25

TO-220

ΦJA = 62.5

 

ID = 24A

 

 

 

 

 

NDP606AL

TJ = 125°C

33

40

 

ΦJC = 1.5

 

 

 

 

 

 

 

 

 

Motorola

VGS = 5V

TJ = 25°C

6

9

TO-263

ΦJA = 62.5

 

ID = 37.5A

 

 

 

 

 

MTB75N03HDL

TJ = 125°C

9.3

14

(D2 PAK)

ΦJC = 1.0

 

 

 

 

 

 

 

Int. Rectifier

VGS = 5V

TJ = 25°C

—

28

TO-220

ΦJA = 62.5

 

ID = 31A

 

 

 

 

 

IRLZ44

TJ = 125°C

—

46

 

ΦJC = 1.0

 

 

 

 

 

 

 

 

 

Int. Rectifier

VGS = 4.5V

TJ = 25°C

—

19

TO-220

ΦJA = 62.5

 

ID = 28A

 

 

 

 

 

IRL3103S

TJ = 125°C

 

31

 

ΦJC = 1.0

 

 

 

 

 

 

 

 

 

 

Note:

1.RDS(ON) values at Tj = 125°C for most devices were extrapolated from the typical operating curves supplied by the manufac- turers and are approximations only.

Two MOSFETs in Parallel

We recommend two MOSFETs used in parallel instead of a single MOSFET. The following significant advantages are realized using two MOSFETs in parallel:

•Significant reduction of power dissipation. Maximum current of 14A with one MOSFET:

PMOSFET = (I2 RDS,ON)(Duty Cycle) =

(14)2(0.050*)(3.3+0.4)/(5+0.4-0.35) = 7.2 W

With two MOSFETs in parallel:

PMOSFET = (I2 RDS,ON)(Duty Cycle) =

(14/2)2(0.037*)(3.3+0.4)/(5+0.4-0.35) = 1.3W/FET

*Note: RDS,ON increases with temperature. Assume RDS,ON = 25mΩ at 25°C. RDS,ON can easily increase to 50mΩ at high temperature when using a single MOSFET. When using two MOSFETs in

parallel, the temperature effects should not cause the RDS,ON to rise above the listed maximum value of 37mΩ.

•No added heat sink required.

With the power dissipation down to around one watt and with MOSFETs mounted flat on the motherboard, no external heat sink is required. The junction-to-case

thermal resistance for the MOSFET package (TO-220) is typically at 2°C/W and the motherboard serves as an

excellent heat sink.

•Higher current capability.

With thermal management under control, this on-board DC-DC converter can deliver load currents up to 14.5A with no performance or reliability concerns.

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Contents DC Voltage Regulation Pentium Pro DC Power RequirementsIntroduction Input VoltagesControls Output Ripple and NoiseEfficiency Processor Voltage IdentificationSimple Step-Down Converter RC5040 and RC5042 DescriptionRC5040 and RC5042 Controllers Main Control Loop Power Good PwrgdOutput Enable Outen Upgrade Present UP#Oscillator Design Considerations and Component SelectionOver-Voltage Protection Short Circuit ProtectionRC5042 Conditions1 Manufacturer & Model # Typ Max Mosfet SelectionTwo MOSFETs in Parallel ThermalMosfet Gate Bias Charge Pump or BootstrapConverter Efficiency Implementing Short Circuit Protection Selecting the InductorShort Circuit Comparator Resistor Discrete MetalDescription Resistor IRC= 2000mi Resistor mΩFor each Mosfet RC5040 and RC5042 Short Circuit Current Characteristics⋅ .2 = 0.74W Schottky Diode Selection Bill of Materials Schottky Diode Selection TableOutput Filter Capacitors Input filter320-6110 PCB Layout Guidelines and ConsiderationsPCB Layout Guidelines Motorola Shottky DiodePC 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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