AMC6821-Q1 Datasheet, PDF (20/54 Pages) Texas Instruments – INTELLIGENT TEMPERATURE MONITOR AND PWM FAN CONTROLLER

AMC6821-Q1
SBAS475 – JUNE 2009 ...................................................................................................................................................................................................... www.ti.com
FAN FAILURE DETECTION
When the TACH data are larger than the TACH low limit, the fan runs at a speed below the predefined minimum
RPM. When this condition occurs, a spin-up process is applied to start the fan again when spin-up is enabled.
Bits [STIME2:STIME0] of the Fan Characteristics Register define this time period. Figure 19 shows the function
of the fan failure detection. Refer to the Fan Spin-Up section.
The fan speed is measured immediately after spin-up; the TACH-FAST bit of Configuration Register 4
determines the monitoring rate. If the fan does not return to a normal range after five consecutive spin-ups, a
FAN-FAILURE occurs; the FAN-FAULT pin goes low when it is enabled (the FAN-FAULT-EN bit of Configuration
Register 1 is set), and the spin-up process continues. If the fan returns to a normal speed range before the fifth
spin-up, the FAN-FAULT pin does not go low even though the FANS bit is still set to '1'. No FANS (fan-slow)
detections are performed during spin-up. After the FAN-FAULT pin goes low, spin-up is performed indefinitely
until the RPM reading returns to within normal range or the spin-up is disabled.
Normal Operation of Fan Failure
Detection and Spin-Up
Yes
Measure RPM
During Spin-Up Process
No
TACH Data > Low Limit
Yes
Bit FANS = 1
Bit FANS = 0
Clear Spin-Up
Time Counter
No
Fan failure, _Yes
FAN-FAULT pin
goes low.
Spin-Up Time Count ³ 5
No
Spin-Up Time Count +1
No Spin-Up if Disabled
Spin-Up Disabled?
Yes
No
Spin-Up Process
Measure the RPM continuously once every 0.25s (TACH-FAST bit = 1) or 1s (TACH-FAST = 0),
even after a fan failure. However, there are no FANS detections during spin-up.
The FAN-FAULT pin is negated if the fan returns to a normal RPM range.
Figure 19. Fan Failure Detection and Spin-Up
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