Fan Management IC

General Description
The MIC502 is a thermal and fan management IC which supports the features for NLX/ATX power supplies and other control applications.
Fan speed is determined by an external temperature sensor, typically a thermistor-resistor divider, and (optionally) a second signal, such as the NLX “FanC” signal. The MIC502 produces a low-frequency pulse-width modulated output for driving an external motor drive transistor. Low-frequency PWM speed control allows operation of standard brushless dc fans at low duty cycle for reduced acoustic noise and permits the use of a very small power transistor. The PWM time base is determined by an external capacitor.
An open-collector overtemperature fault output is asserted if the primary control input is driven above the normal control range.
The MIC502 features a low-power sleep mode with a user-determined threshold. Sleep mode completely turns off the fan and occurs when the system is asleep or off (both control inputs very low). A complete shutdown or reset can also be initiated by external circuitry as desired.
The MIC502 is available as 8-pin plastic DIP and SOIC packages in the –40°C to +85°C industrial temperature range.
Data sheets and support documentation can be found on Micrel’s web site at www.micrel.com.

Features
• Temperature-proportional fan speed control
• Low-cost, efficient PWM fan drive
• 4.5V to 13.2V IC supply range
• Controls any voltage fan
• Overtemperature detection with fault output
• Integrated fan startup timer
• Automatic user-specified sleep mode
• Supports low-cost NTC/PTC thermistors
• 8-pin DIP and SOIC packages

Applications
• NLX and ATX power supplies
• Personal computers
• File servers
• Telecom and networking hardware
• Printers, copiers, and office equipment
• Instrumentation
• Uninterruptible power supplies
• Power amplifiers