 2003 Microchip Technology Inc.

DS21688C-page 1

M

TC670

Features

• Fan Wear-Out Detection for 2-Wire

Linear-Controlled Fans

• Replacement System for 3-Wire Fans

• Fan Alert Signal when Fan Speed is below

Programmed Threshold

• CLEAR Capability for Eliminating False Alarm

• Low Operating Current, 90 µA (typ.)

• Available in a 6-Pin SOT-23 Package

Applications

• Protection for Linear-Controlled Fans

• Power Supplies

• Industrial Equipment

• PCs and Notebooks

• Data Storage

• Data Communications Equipment

• Instrumentation

Package Type

General Description

The TC670 is an integrated fan speed sensor that

predicts and/or detects fan failure, preventing thermal

damage to systems with cooling fans. When the fan

speed falls below a user-specified level, the TC670

asserts an ALERT signal. With this design, a critical

minimum fan speed is determined by the user. The fan

alert level is then set with a resistor divider on the

THRESHOLD pin (Pin 1) of the TC670. When the

minimum fan speed is reached, the ALERT pin (Pin 5)

changes from a digital high to low. This failure detection

works with all linear-controlled 2-wire fans. The TC670

eliminates the need for 3-wire fan solutions.

A CLEAR option can be used to reset the ALERT sig-

nal, allowing the flexibility of connecting the ALERT

output of the TC670 with other ALERT/FAULT inter-

rupts in the system. This feature can be implemented

so that false fan fault conditions do not initiate system

shutdown.

The TC670 is specified to operate over the full

industrial temperature range of -40°C to +85°C. The

TC670 is offered in a 6-pin SOT-23 pin package and

consumes 90 µA (typ.) during operation. The space-

saving package and low power consumption make this

device an ideal choice for systems requiring fan speed

monitoring.

Typical Application Circuit

25

SOT-23A-6

THRESHOLD

GND

CLEAR

SENSE

ALERT

1

3

6

4

From

5

6

+12V

ALERT

LED

DC

FAN

DC

FAN

SENSE

ALERT

2

4

3

1

+5V

0.1 µF

CLEAR

THRESHOLD

GND

Microcontroller

Tiny Predictive Fan Failure Detector