19-2306; 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 Applications Pin Configuration Typical Operating Circuit 3.3V TOP VIEW 12V VCC 10kΩ SENSE 1 8 PGND 7 OFF 3 6 VCC FC- 4 5 FC+ OFF FAIL 2 MAX6684 MAX6684 1µF FC+ FAIL FC- SENSE GND 0.1µF GND PGND 0.1µF SO ________________________________________________________________ Maxim Integrated Products 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. 1 MAX6684 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 critical systems where no fan control, or simple on/off control is desired. The MAX6684 detects fan failure by evaluating 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. 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 ..................................................-0.3V to +28.0V SENSE Current................................................................1400mA Continuous Power Dissipation (TA = +70°C) 8-Pin SO (derate 5.9mW/°C above +70°C)..................470mW Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Junction Temperature ......................................................+150°C Soldering Temperature (vapor phase, 60s).....................+215°C Soldering Temperature (infrared, 15s).............................+220°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = 3.0 to 5.5V, OFF = VCC, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VCC = 3.3V, TA = +25°C.) (Note 1) PARAMETER SYMBOL Supply Voltage VCC Supply Current ICC VCC Shutdown Supply Current ISHDN SENSE-to-PGND Output Low Voltage SENSE-to-PGND Output On-Resistance CONDITIONS V 3.4 mA OFF = GND 10 µA 0.3 0.66 V 1 2.2 Ω 1 10 µA RDSON V FAIL Output Low Voltage I FAIL = 3mA V FAIL Output Leakage Current V FAIL = 5.5V Average SENSE (Fan) Current 0.1 50 SENSE Current Shutdown VCC = 3V Thermal Shutdown of SENSE 15°C hysteresis Fan-Current Fluctuation Frequency No fault detected tFD No fault detected OFF Input High Voltage VIH OFF Input Low Voltage VIL UNITS IFAN = 300mA IFAN = 300mA Minimum Fan-Current Fluctuation Level (Note 2) MAX 5.5 VSENSE = 26V OFF Input Current TYP 3.0 SENSE Leakage Current V FAIL Output Delay After Fault MIN 600 0.8 V 1 µA 300 mA 1200 mA 160 25 °C 400 Hz 0.3 1 2.0 s 15 35 60 mAP-P 0.7 x VCC -10 V 0 0.3 x VCC V 1 µA Note 1: Specifications to -40°C are guaranteed by design and not production tested. Note 2: The MAX6684 is guaranteed to register a fault when the fan current fluctuates less than the minimum; it is guaranteed not to register a fault when the fan current is above the maximum. 2 _______________________________________________________________________________________ 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 0.4 VCC = 3V 0 NO LOAD ISENSE = 300mA 0 VSENSE 2V/div 200 0 -40 -15 10 35 60 85 -40 -15 TEMPERATURE (°C) 10 35 60 85 20ms/div TEMPERATURE (°C) Pin Description PIN NAME FUNCTION 1 SENSE 2 FAIL Active-Low, Open-Drain Fan-Failure Output 3 GND Ground 4 FC- Connect to 0.1µF capacitor for most locked-rotor detection applications. To detect minimum speed, select CF according to Minimum Speed and Locked-Rotor Detection. 5 FC+ Connect to 0.1µF capacitor for most locked-rotor detection applications. To detect minimum speed, select CF according to Minimum Speed and Locked-Rotor Detection. 6 VCC Supply Voltage Input. Bypass VCC to GND with a 1µF capacitor. 7 OFF Active-Low Fan-Control Input. Drive OFF high or leave floating to turn fan on. Drive OFF low to turn fan off. 8 PGND Positive Current-Sensing Terminal. Connect SENSE to low side of fan. Power Ground. Connect to GND. _______________________________________________________________________________________ 3 MAX6684 Typical Operating Characteristics (VCC = 3.3V, TA = +25°C, unless otherwise noted.) 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. MAX6684 Functional Diagram NORMAL FAN OPERATION UNDERCURRENT* FAN ON, FAIL HIGH NORMAL CURRENT 60ms DELAY 1s DELAY OVERCURRENT NORMAL UNDERCURRENT* CURRENT NORMAL CURRENT THERMAL SHUTDOWN NO THERMAL SHUTDOWN 2ms DELAY OVERCURRENT OVERCURRENT FAN ON, FAIL LOW OVERCURRENT THERMAL SHUTDOWN FAN OFF, FAIL LOW THERMAL SHUTDOWN OVERCURRENT 2ms DELAY *INVALID COMMUTATION CURRENT NOTE: A THERMAL SHUTDOWN CONDITION OVERIDES ALL OTHER CONDITIONS, IMMEDIATELY SHUTTING THE FAN OFF AND SIGNALING FAIL. Figure 2. MAX6684 State Diagram Detailed Description The MAX6684 detects fan failure in brushless DC fans. This device is especially well suited for critical systems where no fan control is desired. No software is necessary to control the MAX6684. 4 Fan-Failure Detection Fan failure is determined based on the fan current observed at SENSE. The current observed at SENSE is converted to a voltage, VFAN, and highpass filtered by the capacitor, CF, from FC+ to FC- (Figure 1). _______________________________________________________________________________________ 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. Test Circuit Demonstrates Failure Frequency as a Function of the Value of CF 50 40 30 FAIL LOW 20 10 0 0 100 200 300 400 Figure 5 are only appropriate for the test signals used and do not represent all possible fan waveforms. They are to illustrate the ability of the MAX6684 to discriminate failure due to low fan speed. As a rule, failure typically occurs when the amplitude measured at pin 4 of the MAX6684 drops below 70mV. CURRENT COMMUTATION FREQUENCY (Hz) Figure 4. Current Fluctuation and Commutation Frequency Diagram Undercurrent (AC Component) Fan failure is signaled if the AC component of IFAN is less than 35mAP-P and remains out of specification for at least 1s (Figure 2). The fan remains powered during undercurrent failures. Minimum Speed and Locked-Rotor Detection The MAX6684 asserts FAIL if the fan-current fluctuation frequency is below 25Hz, which corresponds to a fan speed of approximately 700rpm. The fan remains powered during a locked rotor or an under-speed failure condition (Figures 3 and 4). The MAX6684 can be designed to detect fan failure below intended speeds by varying the value of C F. Because of the complexity of fan-current waveforms, the value of CF has to be arrived at empirically and must be verified by bench testing. The guidelines of Overcurrent Protection If an overcurrent condition begins and continues for 2ms, fan failure is signaled for 60ms. During this 60ms period, the power to the fan is turned off. If the part does not enter thermal shutdown and the overcurrent condition continues, power to the fan is turned on every 62ms for 2ms (see Overcurrent Operation in Typical Operating Characteristics). Once the overcurrent condition is removed, the fan is powered continuously. A 0.1µF capacitor between SENSE and PGND prevents the internal DMOS switch from being damaged by back EMF current. Thermal Shutdown A die temperature in excess of +160°C initiates thermal shutdown. In thermal shutdown, the MAX6684 shuts off the fan and the FAIL output asserts. While in thermal shutdown, the MAX6684 monitors the die temperature. Once the die has cooled to below +145°C, the MAX6684 exits thermal shutdown and power is returned to the fan. A thermal shutdown fault condition has precedence over all other failure modes. While the MAX6684 die is over temperature, power is not cycled to the fan, as occurs during overcurrent failure. _______________________________________________________________________________________ 5 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). OFF Drive OFF low to turn off power to the fan. If OFF is tied high or floating, the MAX6684 is enabled. Applications Information Fan Compatibility This device can be used with fans that require operating voltages up to 24V and supply currents up to 250mA. See the Fan-Failure Detection section regarding fan-current waveform issues. Figures 6 and 7 show two ways to increase the current capability of the MAX6684. In Figure 6, a parallel external resistance between SENSE and PGND is used to increase current capability. This method eliminates the fan-control functionality normally associated with the MAX6684 OFF pin. Select the external resistor, R1, such that approximately 100mA flows across the internal RDSON of the MAX6684, which is typically 1Ω. Figure 7 also shows how to use an external currentboost PNP bipolar transistor to increase the current capability of the MAX6684. This method preserves the fan-control functionality of the OFF pin. A 6Ω RBOOST allows approximately 100mA of the fan current to flow through the MAX6684. The MAX6684 is not compatible with fans designed for use with external PWM fan controllers. 6 Fan-Specific Concerns Because fan-current waveforms can vary substantially from one given fan make or model to another, validate the performance of the MAX6684 with the intended fan. It is possible to encounter fans where the MAX6684 is limited to detecting locked-rotor conditions only, because of the nature of the fan-current waveform. In cases where fan-speed detection does not seem to be working properly (although locked-rotor detection is taking place), adding a 100µF capacitor across the fan may solve the problem. When the MAX6684 is used with fans that include locked-rotor protection, the FAIL output is active when the rotor locks, and toggles each time the locked-rotor protection built into the fan attempts a restart, over a timeframe typically measured in seconds. Toggling should be considered an indication of fan failure; conversely, a fan is functioning properly only when FAIL is constantly inactive. Capacitor Selection A ceramic or mylar capacitor, CF, is required from FCto FC+. The capacitor blocks the DC component of the signal, allowing the MAX6684 to monitor the AC current consumption of the fan. See the Minimum Speed and Locked-Rotor Detection section for more information. Power Supply and Bypassing The effects of noise can be minimized by placing a 1µF ceramic bypass capacitor close to the device’s supply pin. _______________________________________________________________________________________ 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 7 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX6684 Chip Information TRANSISTOR COUNT: 3993 PROCESS: BiCMOS