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General Description

The MAX6684 is an integrated fan-failure detector that

detects when a fan exhibits excessive underspeed or a

locked rotor. This device is especially well suited for criti-

cal systems where no fan control, or simple on/off control

is desired. The MAX6684 detects fan failure by evaluat-

ing fluctuations in current at the low side of the fan; no

tachometer signal is necessary. The output of the device,

FAIL, is an active-low, open-drain alarm. The MAX6684

can also be used to switch the fan on or off, based on

the state of a logic-level input, OFF. This device can be

used with fans rated at up to 24V and 250mA. The

MAX6684 is available in an 8-pin SO package, and is

specified for operation from -40°C to +85°C.

Applications

Desktop PCs

Notebooks

Networking Equipment

Telecommunications

Industrial Applications

Features

♦ Dedicated Fan-Failure Detector

♦ Works with Ordinary 2-Wire Fans

♦ No Fan Tachometer Output Required

♦ No Software Development Required

♦ No Analog Circuit Design Required

♦ Logic-Level Fan Driver Control

♦ Works with Fans Rated Up to 24V/250mA

MAX6684

Fan-Failure Detector with Integrated

Power Switch

________________________________________________________________ Maxim Integrated Products 1

FC+FC-

PGND

OFFFAIL

GND

SENSE

TOP VIEW

MAX6684

Pin Configuration

Ordering Information

MAX6684

OFF

SENSE

12V

PGND

GND

FC+

10kΩ

FC-

3.3V

1µF

0.1µF

FAIL

Typical Operating Circuit

19-2306; Rev 0; 1/02

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

PART TEMP RANGE PIN-PACKAGE

MAX6684ESA -40°C to +85°C 8 SO

Summary of content (7 pages)

PAGE 1
9-2306; Rev 0; 1/02 Fan-Failure Detector with Integrated Power Switch Features ♦ Dedicated Fan-Failure Detector ♦ Works with Ordinary 2-Wire Fans ♦ No Fan Tachometer Output Required ♦ No Software Development Required ♦ No Analog Circuit Design Required ♦ Logic-Level Fan Driver Control ♦ Works with Fans Rated Up to 24V/250mA Applications Ordering Information Desktop PCs Notebooks Networking Equipment PART TEMP RANGE PIN-PACKAGE MAX6684ESA -40°C to +85°C 8 SO Telecommunications Industrial Applicati
PAGE 2
MAX6684 Fan-Failure Detector with Integrated Power Switch ABSOLUTE MAXIMUM RATINGS Voltages Referenced to GND, Unless Otherwise Noted VCC ........................................................................-0.3V to +6.0V FC+, FC-.....................................................-0.3V to (VCC + 0.3V) OFF, FAIL ..............................................................-0.3V to +6.0V PGND ....................................................................-0.3V to +0.3V SENSE to PGND ..............
PAGE 3
Fan-Failure Detector with Integrated Power Switch SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT (µA) 1.2 0.8 VCC = 5.5V VCC = 5.5V 275 OVERCURRENT OPERATION MAX6684 toc02 MAX6684 toc01 VCC = 3V 1.6 RDSON (Ω) 300 MAX6684 toc03 RDSON vs. TEMPERATURE 2.0 ISENSE 500mA/div 0A 250 VFAIL 5V/div 225 0.
PAGE 4
MAX6684 Fan-Failure Detector with Integrated Power Switch VCC MAX6684 SENSE OFF VFAN CURRENT-SENSE AND CURRENT-LIMITING CIRCUIT FAULTDETECTION DELAY OSCILLATOR 8.2kHz 8Hz FAIL FC+ CF 70mV R NOISE COMP S BLANK FC- GND Q LATCH PGND Figure 1.
PAGE 5
Fan-Failure Detector with Integrated Power Switch MAX6684 3.3V 100Hz ƒ VCC tFD 10kΩ FUNCTION GENERATOR* OFF FAIL MAX6684 FC+ FAIL CF FC- Figure 3. MAX6684 Commutation Fault Timing Diagram CURRENT FLUCTUATION vs. COMMUTATION FREQUENCY 70 CURRENT FLUCTUATION (AC COMPONENT) (mAP-P) SENSE PGND *35mAP-P SINE-WAVE AC COMPONENT 50mA TO 300mA DC COMPONENT 80 60 GND APPROXIMATE FAILURE FREQUENCIES: CF = 0.033µF < 25Hz CF = 0.01µF < 86Hz CF = 0.003µF < 250Hz FAIL HIGH Figure 5.
PAGE 6
MAX6684 Fan-Failure Detector with Integrated Power Switch 3.3V 3.3V 12V VCC 12V VCC 10kΩ OFF 10kΩ OFF MAX6684 FC+ MAX6684 FAIL CF FC+ FAIL FC- SENSE CF FCGND SENSE PGND RBOOST GND PGND R1 Figure 7. Increased Current Capability Using PNP Transistor Figure 6. Increased Current Capability Using External Resistance FAIL Output The FAIL output is an active-low, open-drain alarm. Three fan-failure modes are possible (see the FanFailure Detection section).
PAGE 7
Fan-Failure Detector with Integrated Power Switch 9LUCSP, 3x3.EPS Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.