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Electronic Design

Thermal-Monitoring Tools Become Hot Commodities In High-End CPUs

High-peformance temperature sensors and fan controllers give designers a better handle on heat management.

With high-end CPU and graphics-processor feature sizes shrinking to 90 nm and less, pressure mounts to find ways to manage the heat. Recognizing this, Standard Microsystems Corp. (SMSC) has unveiled a suite of six temperature sensors and two fan controllers specifically targeting such designs.

The EMC1402, 1403, and 1404 sensors offer interrupt capabilities, while the EMC1422, 1423, and 1424 add system interrupt capability. The 1402 and 1422 are dual temperature sensors; the 1403 and 1423 are triple temperature sensors; and the 1404 and 1424 top out as quad temperature sensors.

The EMC1422, 1423, and 1424 use pull-up resistors on the SYS-SHDN and ALERT pins to shut down temperatures between 77°C and 112°C, enabling system shutdown where software can't be overridden. The resistors are common 10% tolerance parts whose values (depending on the shutdown temperature) can be 4.7, 6.8, 10, 15, 22, and 33 kΩ.

All six temperature sensors operate from 3.3-V supplies and are accurate to within 1°C for external diode temperatures and 2°C for internal diode temperatures. The ICs are compatible with the System Management Bus (SMBus), and advanced features like beta compensation and resistance error correction support 90-nm and 65-nm CPU diodes. Another feature, automatic diode-type detection, targets complex environmental monitoring applications.

While other IC temperature sensors have offset registers that do some fine-tuning for accuracy reasons, SMSC's temperature sensors eschew this feature, saving engineering time. Also, temperature measurements are automatic and accurate.

Since there's no need for additional temperature switches for critical thermal events, the component count is reduced as well. Multiple remote measurements are possible for thermal troublespots on dual-inline memory-memory module (DIMM) cards, wireless cards, TV tuners, and graphics processors.

Three important measurement techniques drive the sensor family's performance: auto beta correction, resistance error correction, and anti-parallel diodes. Beta correction compensates for temperature measurement error found in processors with line widths of 65 nm and lower. It eliminates software configuration for many different remote and processor diodes.

Resistance error correction automatically counteracts the effects of temperature-reading error from series-resistance and substrate diodes and/or pc-board trace errors (Fig. 1). Also, the proprietary anti-parallel diode technology allows two remote temperature monitors to occupy two pins previously used for one monitor.

"Beta compensation and resistance error correction are two major sources of temperature measurement error," says Mitch Polonsky, SMSC's product line marketing manager. He points to Intel's own published data regarding the firm's Pentium 4 CPUs to support his assertion (see the table).

The EMC2101 and 2102 fan controllers work with the SMBus. The basic 2101 suits simple and flexible general-purpose advanced temperature-measurement requirements. The thermally enhanced 2102 integrates linear fan control, four temperature sensors, and hardware-shutdown circuitry in a small form factor.

The EMC2101 single-fan driver offers either a pulse-width-modulated (PWM) or a 1-mA linear output. It has two temperature sensors—an internal sensor accurate to within 1°C and an external sensor accurate to within 2°C. Resistance error correction up to 100Ω is available, as are auto beta compensation and configurability overtemperature limits. The 2101 can accept an external temperature input, too.

"Accepting external inputs like those from hard-disk drives (HDDs) is a very important feature that's not available in general-purpose fan controllers," says Polonsky. The 2101 is designed for applications such as embedded fan control, PWM control, inexpensive fan control, LCD TVs, and VGA cards.

Targeting thermally enhanced fan control, the 2101's closed-loop RPM-based fan control ensures that the fan temperature setpoints are met. This is important for avoiding resonant points in enclosures and maintaining the right speed in aging fans. An integrated 600-mA linear fan driver provides power-up flexibility by allowing a start from 0%, 60%, 75%, or full speed.

In addition, the 2101 provides hardware-configured thermal shutdown and three external 1°C temperature sensors for diode temperatures between 60°C to 100°C. This chip also offers beta compensation, resistance error correction, and programmable temperature limits for an ALERT output pin signal.

The temperature sensors join a growing market for temperature sensing as projected by market analysis firm Databeans. The company expects the 2005 market of $674 million to expand by a compound annual growth rate (CAGR) of up to 11% by 2011, reaching $1.956 billion. These sensors will be used in a number of applications, the largest of which in 2005 was computers.

The EMC1402 and 1422 temperature sensors are housed in eight-pin mini small-outline package (MSOP) cases while the 1403, 1404, 1423, and 1424 come in 10-pin MSOP cases (Fig. 2). They range from $0.60 to $1 each in OEM quantities. The EMC2101 fan controller has an eight-pin MSOP or small-outline IC (SOIC) package, while the 2102 comes in a 28-pin quad flat no-lead (QFN) package. They cost $0.95 to $1.75 each for OEM quantities. Sample quantities of all chips are available.


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