Microchip TC648 Handleiding

Microchip Niet gecategoriseerd TC648

Lees hieronder de 📖 handleiding in het Nederlandse voor Microchip TC648 (8 pagina's) in de categorie Niet gecategoriseerd. Deze handleiding was nuttig voor 23 personen en werd door 2 gebruikers gemiddeld met 4.5 sterren beoordeeld

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 2003 Microchip Technology Inc. DS91063A-page 1

TB063

INTRODUCTION

Less than six years ago, thermal cooling in the

electronics arena was mainly an issue for high-

performance, high-end applications, such as, military,

aerospace and large-scale industrial and medical

applications. Outside these sectors, thermal cooling

was just a premature notion. In the short span of a few

years, technological and other developments have

made thermal cooling necessary for many applications,

thus requiring the development of a new system

management category: thermal management.

This article discusses an integrated fan speed solution

that provides sophisticated speed control of brushless

DC fans, the most popular type of fan used in electronic

equipment, and helps designers get around problems

like acoustic noise, power consumption, mechanical

wear-out and fault detection.

TRENDS AND DRIVERS

On a board level, many more components need cooling

today than even six months ago; with the CPUs having

begun this trend some years ago. Memory chips never

needed cooling, but now SRAM and DRAM packages

require their own cooling solutions. Video card

processors (mostly the 3D type) and other add-in cards

also require cooling, as will the next generation models.

Hard drives, DVD players, CD players and chipsets are

now candidates for cooling as well. In general, board

speeds are becoming faster and boards are becoming

smaller and more heavily populated. Package

densities are increasing and performing more

functions, thus getting hotter.

New developments in digital chip architecture permit

higher system clock rates and additional on-chip

circuitry, causing the chips to run at higher tempera-

tures. A large portion of the power dissipation is the

capacitive charging and discharging during level transi-

tions. Since the power lost is related to the square of

the supply voltage, the trend to lower voltages reduces

power dissipation.

However, higher losses due to higher switching

speeds, significantly offset these savings. An example

is the 486 microprocessor, which was drawing 12 to 15

watts. As PCs moved into the first Pentium®

generation, the microprocessors started dissipating

25W. Today a Pentium® II dissipates about 40W, and

there have been reports that the forthcoming 64-bit

Merced microprocessor dissipates about 65W.

Thermal cooling is also in demand because of the

explosive growth of new embedded applications.

Telecommunications equipment, printers, household

“smart” appliances, and most importantly, networking

equipment (routers, switches and hubs) are only a few

of the products now driven by embedded CPUs. More

are being added each day, and with the complexity of

multiple functions, thermal cooling has become a

necessity.

WHY DO WE NEED COOLING?

The air immediately surrounding a chip initially cools its

surface. That air eventually warms and rises to the top

of the PC or other equipment’s chassis, where it

encounters more warm air. If not ventilated, this volume

of air becomes warmer and warmer, offering no avenue

of escape for the heat generated by the chips.

Typically, a PC chip designed for commercial use can

withstand up to 125°C – 150°C junction temperature,

although a safety margin of a few degrees might be

specified. Exceeding that limit will either cause the chip

to make errors in its calculations or fail completely. A

chip failure or malfunction impacts the entire system’s

operation. Additional cooling also extends component

life by limiting the maximum temperatures the

components are exposed to. In general, a 10°C

temperature reduction will provide a 2:1 increase in

MTBF (Mean Time Between Failure).

Author: George Paparrizos

Microchip Technology Inc.

An Integrated Fan Speed Control Solution Can Lower

System Costs, Reduce Acoustic Noise, Power Consumption

and Enhance System Reliability

TB063

DS91063A-page 2  2003 Microchip Technology Inc.

THERMAL COOLING METHODS

Consistent with the trend of increasing heat dissipation

in electronic systems, the thermal cooling methods

began moving from passive to active solutions. In the

days of the 486 microprocessor, the processor cooling

was implemented by a heat sink and an embedded fan

was only used to cool down the power supply. Since

entering the Pentium era, the processor now produces

enough heat to require a stream of cool air from a fan.

In addition, new 3D graphic cards generate substantial

heat and are also packaged with an embedded fan on

top of the graphic chip.

To date, there are three basic approaches to thermal

cooling: heat spreaders, heat sinks and fans:

1. Heat spreaders, which are made of a tungsten-

copper alloy and are placed directly over a chip,

have the effect of increasing the chip’s surface

area, allowing more heat to be vented upward.

Heat spreaders are frequently designed with a

specific chip in mind.

2. Heat sinks spread the heat upward through fins or

folds, which are vertical ridges or columns that

allow heat to be conducted in three dimensions -

length, width, and height - as opposed to the two-

dimensional length and width of heat spreaders.

Heat sinks maximize the amount of surface area

that can be air-cooled.

3. Fans simply focus the available air on a

concentrated space. The cooling capability of a fan

depends on the volume of air the fan moves, the

ambient temperature and the difference between

the chip temperature and the ambient tempera-

ture. While fans move volume of air, some PC

systems also require blowers to generate air

pressure.

BRUSHLESS DC FANS

Thermal complexity, thermal content and greater power

demands are boosting the popularity of brushless DC

(BDC) cooling fans (Figure 1). In addition to the

advantages of conventional fans, BDC fans have a

significantly higher mechanical reliability. They contain

no rotating commutator/brush assembly to shed dust

particles, wear out, or act as an ignition source.

Additionally, their magnetic coils are stationary and are

usually mounted within a rigid frame for superior

structural integrity and thermal dissipation. Finally, they

lack the rotating magnetic fields of AC motors and the

arching of conventional DC motors and, thus, are

electrically quiet.

While BDC fans adequately evacuate heat from the

system enclosure and are superior to conventional

fans, they add other problems. Such problems that

designers have to cope with in most applications are:

• Fan Mechanical Wear-out

• Acoustic Noise

• Power Consumption

• Fault Detection

The sections that follow provide an in depth summary

of the above mentioned problems and describe the

features, operation and advantages of Microchip’s

integrated fan speed control solution.

FIGURE 1: Brushless DC Fan Basics

Stator

Coil

Stator

Coil

Stator

Coil

Stator

Coil

Internal Control IC

Hall Effect

Sensor

Fan

Frame

Axle

Fan Hub

Center

Bearing Permanent

Magnets

 2003 Microchip Technology Inc. DS91063A-page 3

TB063

FAN MECHANICAL WEAR-OUT

The fan is a complex electromechanical device and, in

most cases, requires replacement before the lifetime of

its host system expires. In the majority of cases, the fan

failure is caused by the failure of the bearing, due to

heat and mechanical wear. Other causes include

blockage by foreign objects and electrical failures.

Fan failure is a very important issue for the manufac-

turer in terms of end-product reliability and quality. A

fan replacement reduces the customers’ perception of

product quality and increases their indirect expendi-

tures. The cost of a replacement part (fan), the installa-

tion cost and the opportunity cost associated with the

non-utilization of the equipment can add up to a

significantly higher cost for the user. Therefore, from an

economical standpoint, a solution that ensures a longer

fan service life is a value-added feature of the

equipment and a good marketing tool.

Microchip’s fan controller ICs provide sophisticated

temperature-proportional, fan speed control. The fan

runs only as fast as is required to keep the system cool.

This extends the service life of the fan because it is not

subject to the stress imposed by continuous full-speed

operation and speed changes are gradual (vs. an on/off

operation). A typical speed control solution can be

expected to have a mean time between failure (MTBF)

far greater than a typical fan running at full speed.

Figure 2 demonstrates the fan life versus speed rela-

tionship by showing the L10 life values (the time at

which one expects 90% of the fan population to

survive) of a sleeve-bearing fan running at several

speeds and different operating temperatures. A 35%

speed reduction more than doubles the L10 life values,

independent of the operating temperature. These

savings are attributed solely to lower average operating

speeds. In addition to these quantifiable benefits, one

should expect significantly higher L10 life values from

gradual fan speed changes versus conventional

aggressive on/off operation. An on/off operation

generates shocks, resulting in a hostile environment for

the fan’s structure and/or bearing system.

Ball-bearing fans perform better in terms of L10 life

values. However, they also cost significantly more

than sleeve-bearing fans.

FIGURE 2: Fan Life vs. Fan Speed

ACOUSTIC NOISE REDUCTION

Noise is another important factor in the perceived

quality of a product. Everything else held constant, a

quieter product will always be preferred over a louder

one. Noise reduction is a challenging task for

designers, yet it is a differentiating attribute for the

marketing of the product.

The most dominant source of acoustic fan noise is

turbulent airflow, which is caused by fan operation at

full speed. Employing fan speed control, where the fan

is operating primarily at lower than full speed,

minimizes this noise. The second most dominant

source of acoustic noise is due to the BDC fan’s torque

characteristics. In this case, stator excitation causes a

small amount of ripple in motor torque at the frequency

of commutation, which again leads to a “ticking” noise.

Correcting noise problems becomes an even greater

challenge when moving to multiple-fan applications. If

you package several chassis in a rack and put several

racks in a room, the combined noise can be deafening.

Most designers choose fans for worst case thermal

conditions, which has a downside effect under normal

thermal operation: additional, unnecessary acoustic

noise.

A small change in fan speed causes a significant

change in fan noise. The formula used to determine the

noise level, when the fan is running at speed S (% of

SMAX), is as follows:

EQUATION:

A typical fan (120 ft3/minute – 4.7”) has a full speed

noise rating of about 45 dB. Running the fan at half

the speed results in a significantly lower noise level

of 30 dB. This 15 dB change is perceived by the

human ear as an approximately 70% noise

Fan Life vs. Fan Speed

L10 Life (k Hours)

Fan S

eed

(

RPM

)

120

100

2900 2450 2090

40 C°

50 C°

60 C°

70 C°

3320

140

LS = L1 + 50 log S

Where LS is a weighted noise level at fan speed S

and L1 a weighted noise level at full speed.

Product specificaties

Merk:	Microchip
Categorie:	Niet gecategoriseerd
Model:	TC648

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