issue: January 2008 APPLIANCE Magazine
Tight Fan Motor Control in Small Packages
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Closed-loop fan controllers and temperature sensors help OEMs accelerate product development.
The EMC210x family of fan controllers employs RPM closed-loop control and manages multiple temperatures. The supplier, SMSC (Hauppauge, NY, U.S.), also launched three SMBus temperature sensors for systems requiring a high level of temperature monitoring. All of the devices were designed for the smaller geometries, such as 45 nm, that are typically associated with this level of monitoring. Applications include flat-screen TVs, PCs, printers, and servers.
To reduce design and prototype validation time, the fan control ICs provide increased reliability to a system’s thermal management by shifting the role of constant supervision off of the microprocessor. Once configured, alerts bring only those events requiring action to the attention of the host processor. Fan spin-up, restriction over sudden changes in fan speed, and tracking fan speed to temperature are achieved without extensive software overhead or constant processing.
The fan controllers’ closed-loop RPM control schemes are designed to significantly improve control of the fan speed versus open-loop fan drive methods. By measuring the fan speed with a closed loop, fan control set points are met with 5%-or-better accuracy. The fan speed is also maintained over the life of the product. This is beneficial when taking into account that an aging fan will change its response to a given drive signal over time. Lastly, resonant or vibration speeds can be avoided in enclosures.
The fan controllers have increasing levels of hardware management to meet most system shutdown and temperature measurement needs. The EMC2105 and EMC2106 offer linear fan drivers that integrate the field-effect transistor (FET) from the system and are capable of driving up to 600 mA. The EMC2103 and EMC2105 are suited for one-fan systems. Alternatively, the EMC2104 and EMC2106 can drive two fans by applying a second pulse-width-modulation (PWM) signal. This signal can also be used for other applications such as screen brightness or an LED driver.
The EMC210x family’s temperature measurement technology is compatible with the latest generation of processor geometries. This includes automatic beta compensation that will detect the requirements of a thermal diode and self-configure the measurement attributes for an accurate reading. Resistance error correction adjusts for common series resistance found in substrate diodes and traces that would otherwise lead to measurement error.