May 1999

163

MIC502

MIC502

Micrel

MIC502

Fan Management IC

Advance Information

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

• Uninterruptable power supplies

• Power amplifiers

Ordering Information

Part Number

Temperature Range

Package

MIC502BN

–40

°C to +85°C

8-pin Plastic DIP

MIC502BM

–40

°C to +85°C

8-pin SOIC

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 sec-

ond 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.

Typical Application

VT1

CF

VSLP

GND

VDD

OUT

OTF

VT2

1

2

3

4

8

7

6

5

R1

T1

R3

R4

R2

12V

Overtemperature

Fault Output

MIC502

Secondary

Fan-control

Input

Fan

Q1