Sensing temperature is critical to many systems for protection and optimized performance. However, today's microprocessors designed with the latest 65 nm processing technology have made temperature sensing, communication, and control an integral part of the system. To measure and communicate both temperature and voltage, Intel Corp. and Analog Devices collaborated to create the Simple Serial Transport (SST) bus. The single-wire SST bus communicates the measurements to the core logic or external fan-speed controllers to extend the performance and improve reliability in PCs, servers and workstations. Intel also defined the Platform Environmental Control Interface (PECI), a proprietary derivation of SST, as a single-wire serial bus to communicate only temperature data. These new protocols communicate sensor data from both internal and external temperature measurements.
DIGITAL TEMPERATURE SENSING
Andigilog's aSC7521 SST remote digital temperature sensor uses CMOS technology to target PC hardware monitor applications. The unit's 3-state address pins set one of nine SST bus addresses. The two address pins allow the unit to distinguish multiple sensors on the same bus. The local sensor has an accuracy of ±2C maximum over the temperature range of 40 to 70C with VDD = 3.3V and ±3C maximum over –40 to 125C. The remote sensor accuracy is ±1C maximum over a temperature range of 50 to 70C with an ambient temperature range of 0 to 70C and VDD = 3.3V and ±3C maximum over –40 to 125C with an ambient temperature range of 0 to +70C. Total monitoring cycle time for all temperature measurements is 0.2 second. The unit's MSOP-8 surface mount package takes only 3.05 × 5.05-mm maximum board space. Get more information on Andigilog's aSC7521 Low-Voltage 1-Wire Digital Temperature Sensor.
SENSING THE COMPUTER CHIP'S TEMPERATURE
Among the 291 million transistors on the 143-mm2 Intel Core™ 2 Duo processor, a few are used to provide integrated Digital Thermal Sensors (DTS) for more efficient processor and platform control. Located within the processor, the thermal sensors continuously measure the maximum temperature on the chip. Used with Intel's Quiet System Technology, included in the Intel 965 Express Chipset family, the DTS regulates the system and processor fan speeds. The temperature monitoring provides safe operating temperature for the processor and lower acoustic noise since fans operate at the minimum speed required to cool the system. Intel's PECI bus communicates the DTS data. The Intelligent Power Capability achieves up to 40 percent more energy efficiency than previous Intel dual-core processors. Get more information on Intel's Digital Thermal Sensors (and the Core™ 2 Duo processors).
TEMPERATURE AND VOLTAGE SENSING AND MONITORING
Communicating over the SST bus at speeds over 1 Mbps, Analog Device's ADT7485A monitors its own temperature as well as the temperature of a remote sensor diode. The unit can also monitor its supply voltage and four external voltage channels. Operating from a 3.3V supply, the 10-bit ADC has Total Unadjusted Error (TUE) (including multiplexer and attenuators) of ±2 percent for both 12 and 5V channels. The internal (local) sensor has an accuracy of ±1.75C maximum over the temperature range of 40 to 70C with VCC = 3.3V ±5 percent and ±4C maximum over –40 to 100C. The remote sensor accuracy is ±1C maximum over a temperature range of –40 to 125C with an ambient temperature of 25C and VCC = 3.3V, ±1.75C maximum from –40 to 125C with an ambient temperature of range of –40 to 70C and VCC = 3.3V ±5 percent, and ±4C maximum over –40 to 125C with an ambient temperature range of –40 to 100C. With averaging enabled, the conversion time for the voltage input is 11µsec, for the local temperature is 12 µsec, and for the remote temperature is 38 µsec. Get more information on Analog Devices' ADT7485A SST Digital Temperature Sensor and Voltage Monitor.