View max6684 datasheet:

19-2306; Rev 0; 1/02 Fan-Failure Detector with Integrated Power Switch General Description Features The MAX6684 is an integrated fan-failure detector that Dedicated Fan-Failure Detector detects when a fan exhibits excessive underspeed or a Works with Ordinary 2-Wire Fans locked rotor. This device is especially well suited for criti- cal systems where no fan control, or simple on/off control No Fan Tachometer Output Required is desired. The MAX6684 detects fan failure by evaluat- No Software Development Required ing fluctuations in current at the low side of the fan; no tachometer signal is necessary. The output of the device, No Analog Circuit Design Required FAIL, is an active-low, open-drain alarm. The MAX6684 Logic-Level Fan Driver Control can also be used to sw