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Thermal Management Solutions Dave Hanrahan Applications Engineer PowerPoint PPT Presentation


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Thermal Management Solutions Dave Hanrahan Applications Engineer. Agenda. A look at the Thermal Problem Thermal Diode Monitoring (TDM) Techniques Thermals vs. Acoustics - associated tradeoffs Distributed Temperature Sensing Automatic Fan Speed Control Demo Wrap-up. The Thermal Problem.

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Thermal Management Solutions Dave Hanrahan Applications Engineer

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Thermal Management Solutions

Dave Hanrahan

Applications Engineer


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Agenda

  • A look at the Thermal Problem

  • Thermal Diode Monitoring (TDM) Techniques

  • Thermals vs. Acoustics - associated tradeoffs

  • Distributed Temperature Sensing

  • Automatic Fan Speed Control

  • Demo

  • Wrap-up

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The Thermal Problem

  • Equipment required to operate in harsh environments

  • High Reliability: - demand for 24-7 operation

  • System down-time can cost $$$$

  • Need to reduce TCO (Total Cost of Ownership)

  • Trend is towards increased component power and component density on cards/modules

  • Need for predictive failure: - allows equipment to report potential problems before they actually occur

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The Thermal Problem: - sources of heat

Common to have 100W - 200W to be dissipated

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The Thermal Problem:- Design Constraints

  • Multiple boards in cabinets restrict airflow: - require many fans to deliver adequate volumetric cooling

  • Low profile systems constrain the amount and physical size of cooling fans limiting CFM delivery

  • Multiple fans will heavily contribute to system noise and current consumption

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Thermal Diode Monitoring (TDM)

  • A base-emitter PN junction has an inherent temperature dependency which is described by the following equation: - VBE = kT/q * ln (Ic/Is)

  • PN junction voltage changes by -2mV/°C

  • Need to extract this low level signal

  • Remove diode offset

  • Filter Noise

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TDM Sampling Input Stage

D- is biased a diode drop above GND

I = 12mA, N = 17

Input Low pass filter 65kHz

C1 is optional for noisy environments

Results averaged over 16 conversions

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Temperature from VBE

  • VBE = kT/q * ln (Ic/Is)

  • VBE1-VBE2 = DVBE =(kT/q) (ln (I/NI)

  • Since I,N, k, q are all known constants then

  • DVBE = (Constant) (T)

  • or T = (Constant) (DVBE)

  • Simple transistor can be used to measure temperature

  • 2-wires can connect to transistor several feet away

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Temperature Sensing: 1C Accuracy

+3.3V

2N3904

SMBus

Alert

Over-temperature

turns on fan

full-speed

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Thermals vs. Acoustics

  • Active cooling makes use of fans to push air

  • No. fans required depend on: -

    • system thermal profile

    • physical size of system

  • The greater the no. fans, the better the cooling, but to the detriment of acoustics

  • Automatic Fan Speed Control reduces acoustic noise by optimizing fan speed for measured temperature

  • Reduces system current consumption

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Why implement Fan Speed Control?

  • Reduce Acoustic Noise

  • Reduce Current Consumption

  • Increase Fan Life

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Thermals vs. Acoustics

  • Are there Acoustic Noise Standards to be adhered to?

  • ISO 7779: - Noise Emitted by Computer & Business Equipment

  • BLUE ANGEL specs

    • http://www.nemko.no/s_environmental/engel.html

  • Acoustic Noise Emitted by Telecommunications Equipment

    • http://www.etsi.org/(ETS 300 753)

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ISO7779 Measurement Method

Bystander

30°

Operator

  • Operator Position - 1.2m from floor, 0.25m from equipment

  • Bystander Position - 1.5m from floor, 1m from equipment

30°

0.25m

1m

1.5m

1.2m

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Acoustic Standards - Blue Angel

  • Blue Angel specs propose that a PC be no louder than 48dBA in idle state, i.e. with no hard disk or other drive activity.

  • In the active state, i.e. when the hard disk or another drive is being accessed, the machine should be no noisier than 55dBA.

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Acoustic Standards - Telecommunications Equipment (ETSI)

* Measurements taken in accordance with ISO7779

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Any shortcomings/concerns?

  • Specs merely define max “static” noise or noise averaged from equipment over a time period e.g. 24 seconds.

  • However, a fan may be running quieter than noise limit, but may still be cycling up and down, annoying the user.

  • Require some method to account for “dynamic noise behaviour” or rate of change of noise.

  • Filtered Automatic Fan Speed Control Mode is a mechanism with which to defeat this problem.

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Fan Noise vs. Temperature

Fan Speed Control reduces noise

Auto Fan

Speed

Control

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Distributed Temperature Sensing

  • All Temperature Monitoring devices are intelligent, 2-wire bus-based

  • Multiple address selection allows up to 9 devices to be placed on a single bus

  • Multiple remote temperature measurement capability

  • Low cost and extremely small package options

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Distributed Temperature Sensing

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Automatic Fan Speed Control

  • A single temperature or all temperatures can control the fan speed.

  • Fan Speed varies automatically with temperature.

  • Only 2 parameters required: TMIN & TRANGE

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Automatic Fan Speed Control

TRANGE

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Effect Of TRANGE Value

13.33% / °C

0.833% / °C

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Filtered Auto Fan Speed Control Mode

  • Allows fan to ramp up or down smoothly to new speed

  • Less acoustic pollution since fan is not cycling up and down with fast temperature transients

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ADM1026 Systems Monitor ASIC

  • Up to 17 Voltage Measurement Channels for PSUs

  • Up to 8 Fan Speed Measurement Inputs

  • Up to 17 GPIOs

  • Remote Temperature Measurement (2 channels)

  • On-chip Temperature Sensor

  • Linear & PWM Fan Speed Control o/p’s

  • 8kB on-chip EEPROM

  • Chassis Intrusion Detection

  • Reset Input, Reset Outputs

  • Automatic Fan Speed Control

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ADM1026

  • Complete systems monitoring solution

  • Monitors system temperatures, voltages and fan speeds

  • EEPROM holds FRU information

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ADM1026 Software Demo

Evaluation software available for all products

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ADM1029 Scaleable, Intelligent Fan Controller

  • Programmable & Automatic Fan Speed Control

  • Dual Fan Speed Measurement

  • Supports Backup & Redundant Fans

  • Supports Hot Swapping of Fans

  • Cascadable Fault Output (CFAULT) for multiple device communication

  • Local & Remote Temperature Monitoring

  • Small 24-pin QSOP package

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ADM1029 Scaleable, Intelligent Fan Controller

  • Fan Free-Wheel Test

  • All Faults, Alarms Are fully Maskable

  • Up to 8 Devices may be addressed in a system using a single address pin (controlling up to 16 Fans)

  • Normal, Alarm & HotPlug speeds are all programmable

  • OFFSET Registers allow offset values to be added to default temperature measurements

  • 15.625Hz, 62.5Hz, 250Hz, & 1kHz PWM drive frequencies available

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ADM1029 Application Circuit

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ADM1030/ADM1031 Intelligent Temperature Monitor/Fan Controllers

  • Programmable & Automatic Fan Speed Control

  • RPM Mode to maintain constant fan speed

  • Remote Temperature Measurement accurate to 1C

  • 0.125°C Resolution on Remote Temperature channel

  • Local Temp Sensor with 0.25°C Resolution

  • Pulse Width Modulation (PWM) Fan Control

  • Programmable PWM Frequency (10Hz to 100Hz)

  • Tach Fan Speed Measurement for 3-wire fans

  • Analog input measures speed of 2-wire fans

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ADM1030/ADM1031 Features

  • Programmable PWM duty cycle (0% to 100%)

  • Over Temperature (THERM) output

  • Filtered Mode helps dynamic acoustic variations by filtering fans response to temperature transients

  • FAN_FAULT output signals catastrophic fan failure to system

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ADM1030 Application Circuit

N.C. pins represent 2nd temp. & fan channel on ADM1031

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For more information:

  • www.analog.com/pc

  • www.analog.com/temp-sensors

  • email: [email protected]

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