Really Cool Fan Control IC Drives Green Wind

The MLX90287 features a one-chip solution for driving low noise speed-controlled single-coil brushless cooling fans. With an operating supply voltage from 4.5V to 16 volts, the MLX90287 targets the widely used 12 volt cooling fan applications. With the integrated power stage, cooling fans rated as high as 550mA (continuous) can be easily driven addressing a majority of applications. The device is even able to operate within an ambient temperature from -40 to 150 degree Celsius, making it suitable for harsh environments like automotive, industrial, military and aerospace. .

The ultimate step in energy-efficient cooling designs is to control and optimize cooling fan rotation speed depending on the system thermal load. Taking the example of a computer processor, while regular office work creates low system load, on the contrary playing intense 3D games requires the highest system load. Hence constantly keeping the maximum cooling capabilities leads to a waste of energy and high acoustic noise from the fan airflow.

The MLX90287 provides a simple solution for controlling cooling fan speed via digital or analog techniques. Latest cooling architectures for CPU cooling use high frequency pulse width modulation (PWM) signal where the applied duty cycle is proportional to the desired cooling speed. Unlike other solutions, the MLX90287 directly accepts, without any external circuitry, a wide PWM frequency range from 100Hz to 100KHz. This suits perfectly the latest systems using typically 25KHz or above and older systems still using lower frequency. Other architectures use analog signal or even temperature sensor control. The MLX90287 can regulate cooling fan speed via a mere potentiometer, a solution used by many extreme gamers for total control, or even a simple thermistor for a more automatic regulation responding on the real system temperature.

Frequently system architects must find a solution to maintain minimum fan rotation speed in cases of system failure or system standby mode. The MLX90287 provide a flexible and effortless solution for minimum speed setting using an external resistor divider. With just two inexpensive resistors and nothing more, full freedom of minimum speed setting is possible. In case no minimum speed setting is required, then those two resistors are simply not required. It’s that simple.

A common issue of cooling fans is the high peak or stall current occurring from the zero speed until nominal rotation speed. Such peak is usually 2 to 3 times higher than the average current consumption during normal rotation. Hence system designers are forced to consider it for power supply requirements and system reliability. The MLX90287 integrates a soft-start mechanism to intelligently manage peak start-up current. Conventional soft-start schemes linearly raise the power applied from zero to full power over a certain period of time. This method has clear disadvantages for bigger cooling fans. At low power, such schemes may not start the fan rotating due to mechanical inertia. But then the fan may drive to full power, even if the system needs just half or less, thus wasting energy. The MLX90287 intelligent soft-start applies, from the beginning, just enough power to overcome mechanical inertia and enable immediate rotation. Then while raising power, the MLX90287 monitors the rotor magnet transitions with its integrated Hall sensor, adapting the power based on the system needs. As a result, the MLX90287 allows any kind of cooling fan to start properly at the lowest specified rotation speed while suppressing high peak start-up current.

The MLX90287 includes on-board the latest low noise techniques employed by Melexis Fan Driver ICs. As introduced in the recent MLX90285, the Melexis “Active” Soft-Switching technology automatically optimizes the low noise capability depending on the fan rotation speed. Thus high motor efficiency and low noise are reached at high rotation speed, while even lower noise is achieved at low rotation speed. Soft switching makes possible “whispering” cooling fans even with low system loads.

The MLX90287 is delivered with the Tachometer (FG – Frequency Generator) short-circuit protected open drain output used for rotation speed computation. The device provides as well reverse voltage protection over the full supply and built-in locked rotor protection to prevent motor coil overheating in case of mechanical blockage. Thermal protection is also included to best protect the device against abnormal temperature rise caused by motor coil short-circuit. Last and not least, high electrostatic discharge (ESD) rating of more than 6000 volts (Human Body Model) delivers a comfortable safety margin against potential risks of damage during module assembly or usage.

The MLX90287 is available in an 8-pin surface mount “SOIC” package. Melexis SOIC package is respectful of the environment and fully “Green” compliant including notably RoHS (Restriction of Hazardous Substances), Lead-Free (Pb-Free) and Halogen-Free compliance.

Bringing a host of benefits along with ease of use, the MLX90287 is a remarkable speed-controlled fan driver IC solution. Directly PWM compatible with Intel’s PWM Fan Specification, analog and temperature speed control regulation available in one and the same device, the MLX90287 offers the highest level of flexibility and integration in one-chip for a wide range of cooling fan applications.

The MLX90287 is available for high volume production with engineering samples available on request.