Most people have experienced electrostatic discharge (ESD) in the form of a small shock after walking across a carpet. But when ESD zaps electronic devices, such as cooling fans, failure usually follows within a short time. Cooling fans are a critical part of PCs. When fans fail, computers often work for a while but then become intermittent, depending on the design. A new single-chip, three-lead fan controller, The US79, from Melexis USA, Concord, N.H., protects against ESD and other failures.
The US79 reduces cooling electronics from eight components to just one. The chip, which mounts directly to the fan motor simplifying fan assembly, has no power supply pin. By eliminating this -- typically the most vulnerable pin on the IC -- ESD tolerance goes from 3,000 V to 15,000-25,000 V, and from 3,000 to 7,000 V at the IC pins. Power is supplied through a motor coil, which provides an ESD filter and protects from overvoltage and reverse voltage.All other components and their 16 solder joints have been replaced by just three connections in the US79. The IC operates at low temperatures using power MOS outputs and CMOS signal processing. Locked rotor protection shuts the motor drive off for 5 sec if no motion is detected for 1 sec. This continues until the locked rotor is fixed, preventing overheating and eliminating dead-angle failures.