AMC6821 datasheet(29/54 Pages) TI

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ReadLocal

Temperature

Yes

LTH=1,

LTO=1

Yes

Temperature ³

Local-Critical-Temp

LTC=1,

isLow

OVR

LTL=1,

LTO=1

Yes

RTL=1,

RTO=1

Yes

ReadRemote

Temperature

RTH=1,

RTO=1

Yes

RTC=1,

OVR isLow

Yes

(UpdateDCYwiththeratedefinedbythe

bits[RATE2:

0]oftheDCYrampregister.

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

CalculateNewDCYfortheRemote

FanTemperatureControl

Yes

CalculateDCYfortheremotefantemperaturecontrol

andlocalfantemperaturecontrol,respectively.

UsethelargeroneasthenewDCY.

RemoteFanTemperatureControlMode

UpdateDCY

(RemoteFanTemperatureControl)

(Maximumfastspeedcalculatedcontrol)

UpdateDCY?

Yes

ThetemperatureupdatingratemaybefasterthantheDCYupdatingrate.

AMC6821

SBAS386C – MAY 2006 – REVISED JULY 2007

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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