Datasheet

ReadLocal
Temperature
No
Yes
LTH=1,
LTO=1
Yes
No
No
Temperature ³
Local-Critical-Temp
LTC=1,
isLow
OVR
LTL=1,
LTO=1
Yes
RTL=1,
RTO=1
Yes
ReadRemote
Temperature
RTH=1,
RTO=1
Yes
No
RTC=1,
OVR isLow
Yes
No
No
(UpdateDCYwiththeratedefinedbythe
bits[RATE2: 0]oftheDCYrampregister.RATE
Temperature ³
Remote-Critical-Temp
Temperature ³
Remote-High-Temp-Limit
Temperature £
Local-Low-Temp-Limit
Temperature ³
Local-High-Temp-Limit
Temperature £
Remote-Low-Temp-Limit
CalculateNewDCYfortheRemote
FanTemperatureControl
Yes
CalculateDCYfortheremotefantemperaturecontrol
andlocalfantemperaturecontrol,respectively.
UsethelargeroneasthenewDCY.
No
RemoteFanTemperatureControlMode
UpdateDCY
(RemoteFanTemperatureControl)
(Maximumfastspeedcalculatedcontrol)
UpdateDCY?
Yes
No
ThetemperatureupdatingratemaybefasterthantheDCYupdatingrate.
AMC6821-Q1
www.ti.com ...................................................................................................................................................................................................... SBAS475 – JUNE 2009
When the actual duty cycle is different from the desired value, the duty cycle is adjusted automatically. When the
RAMPE bit of the DCY-RAMP Register is cleared ('0'), the duty cycle changes to the desired value immediately
after being calculated. When the RAMPE bit is '1', the duty cycle changes to the new value gradually.
The DCY-RAMP Register specifies how quickly the duty cycle changes. The duty cycle can be checked every
0.0625 second to every eight seconds, depending on the bits [RATE2:RATE0] bits. It changes 1/255(0.392%) to
4/255 (1.57%) each time, depending on the bits [STEP1:STEP0] bits. When the difference between the actual
value and the target value is equal to or less than the adjustment threshold (as defined by the bits
[THRE1:THRE0] bits), the adjustment finishes. See the DCY-RAMP Register for details. When the TACH
monitoring is enabled (TACH-EN bit, bit 2 of 0x02, is set to '1') and the TACH-MODE bit (bit 1 of 0x02) is cleared
('0'), the duty cycle is forced to 0% when the calculated value is less than 7%. If the TACH monitoring is disabled
(TACH-EN = 0) or the TACH-MODE bit is set ('1'), the duty cycle is always set to the calculated value even if the
value is less than 7%.
Figure 29. Temperature Monitoring Flow Chart
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