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Smart, small fan controllers and temperature monitors support PCs, embedded systems
By Margery Conner, Technical Editor -- EDN, 8/23/2007
As power density increases in workstations and embedded systems, system controllers require more sophisticated temperature-control and device-monitoring capabilities. Addressing those needs, SMSC has introduced the EMC1046/47 and EMC1428 SMBus temperature monitors and the EMC2103/4/5/6 family of fan controllers. Both product families incorporate the company’s three proprietary high-accuracy measurement techniques—automatic beta compensation, antiparallel-diode technology, and resistance-error correction—to ensure 1°C accuracy.
Traditional temperature sensors require transistors with a flat gain, or “beta.” However, at 45-nm geometry, transistor beta varies nonlinearly with the transistor’s collector current, thus varying temperature accuracy. SMSC’s automatic-beta-compensation method relies on measuring high and low collector currents it injects into the measurement transistor. This method meets transistor-model-measurement standards that Intel requires for its systems based on 45-nm and smaller technologies. The second technique, antiparallel-diode technology, allows you to measure multiple remote diodes with just two pins. The third technique addresses the fact that substrate diodes and board traces add series resistance. SMSC’s resistance-error-correction technology compensates for this resistance without the need for measuring the traces and calculating compensation.
In addition to these techniques, the EMC2103/4/5/6 family of fan controllers uses closed-loop-rpm fan control with look-up tables to offload fan control from the system controller. Measuring the fan speed within a closed loop allows you to meet fan-control setpoints with 5% or better accuracy and maintain those setpoints over the life of the product. This feature is essential because an aging fan changes its response to a given drive signal over time. The EMC2105 and EMC2106 incorporate linear fan drivers that integrate the FET from the system and can drive as much as 600 mA. The EMC2103 and EMC2105 target use in one-fan systems, and the EMC2104 and EMC2106 can drive two fans by applying a second PWM (pulse-width-modulation) signal. An EEPROM can configure these fan controllers for systems without a host controller.
The EMC210x family ranges in price from $1.20 to $1.80 each, and SMBus temperature sensors range in price from $1 to $1.40 (10,000) each.
