Fan motor driver claims to be first to feature an integrated Hall sensor and digital AGC function

December 06, 2012 // By Paul Buckley
ROHM has developed new fan motor drivers with built-in Hall element which is ideal for driving cooling fans in notebook PCs, tablets, and gaming systems.

The BU6904GF/NUX and BU6906GF/NUX drivers are the first to include a digital AGC (Automatic Gain Control) function that contribute to not only greater miniaturization and lower power consumption, but reduced drive noise for silent operation.

The increasing complexity and speeds of electronic devices increase the demand and applicability of cooling fan motor drivers. However, due to motor characteristics such as signal detection accuracy it has become commonplace up to now to utilize a discrete 2-chip configuration consisting of a separate Hall IC and motor driver. But the trend towards decreased size and greater miniaturization requires smaller, thinner components and fewer external parts, making it necessary to develop a driver IC that integrates a Hall element.

In response, ROHM utilized CMOS processes and original circuit technology to minimize the chip size. In addition, the drivers, which incorporate a Hall element that eliminates the need for a separate Hall device, are equivalent in size and thickness with conventional Hall ICs, reducing mounting area considerably. An digital AGC function is included – an industry first, along with linear Hall signal detection combined with PWM soft switching drive minimizes Hall signal waveform fluctuations for improved circuit efficiency and noise characteristics.

ROHM claims the devices are the industry’s first driver featuring an integrated Hall element and digital AGC function (AGC-based gain correction improves noise characteristics).

Hall signals are susceptible to environmental changes within the fan motor, which can result in amplitude variations. For example, when the rotor in the fan motor rotates the amplitude moves up or down by a certain amount. Unsurprisingly, when the distance is close the sensitivity goes up, along with the Hall amplitude. In addition, differences in the strength of the magnet’s magnetic field can affect the temperature characteristics of the Hall element. The built-in AGC function corrects the amplitude for optimal performance and noise characteristics.

Visit ROHM Semiconductor at