AMC6821 Datasheet, PDF (40/47 Pages) Burr-Brown (TI) – Analog Monitor and Control Circuit

AMC6821
SBAS386A – MAY 2006 – REVISED MAY 2006
www.ti.com
Updating Rate Bits: [RATE2:RATE0]
These bits define the rate (time/sec) that the duty cycle is recalculated in the auto temp-fan control mode. The
value of [RATE2:RATE0] does not affect the ADC conversion rate. Both external and local temperature readings
are updated continuously, even if the DCY is updated slowly.
The RPM monitoring rate and DCY updating rate in the software RPM control mode are specified by the
TACH-FAST bit of Configuration Register 3. The [RATE2:RATE0] bits are ignored in this mode.
Adjustment Threshold Bits: [THRE1:THRE0]
These bits determine the threshold of the duty cycle adjustment in the auto temp-fan control mode, and are
ignored in all other modes. When the auto fan temperature control loop is active, the duty cycle is not adjusted if
the required adjustment is less than or equal to the threshold defined by bits [THRE1:THRE0]. This provides a
hysteresis to improve the control stability. For example, if the current duty cycle is 50% and the desired value is
71%, the total required increment is 21%. If the step is 4/256 and the threshold is 2/256 (0.78%), the duty cycle
reaches 70.31% after 13 updates, 0.6875% less than the desired value. This difference is less than the
threshold (0.78%); therefore, the adjustment stops. However, if the threshold is 1/256 (0.39%), then one more
update occurs, and the duty cycle increases by 0.39% (1LSB) because 0.39% (1LSB) < 0.6875% < 0.78%
(2LSB). Finally, the duty cycle reaches 70.7%, 0.3% less than the desired value because of the limitation of 8-bit
resolution.
Note that bits [THRE1:THRE0] are ignored in the software RPM control. In this mode, the DCY adjustment stops
when the difference between the TACH data and TACH setting is less than or equal to 0x000A.
TEMPERATURE DATA REGISTERS
Local Temperature Data Register Bits: [LT10:LT0]
Bits [LT10:LT0] are the newest local temperature reading.
Remote Temperature Register Bits: [RT10:RT0]
Bits [RT10:RT0] are the newest remote temperature reading.
Temp-DATA-LByte Register (Address 0x06, Value After Power-On or Reset = 0x00)
Bit 7 (MSB)
LT2
Bit 6
LT1
Bit 5
LT0 (LSB)
Bit 4
0
Bit 3
0
Bit 2
RT2
Bit 1
RT1
Bit 0 (LSB)
RT0
Bits [LT2:LT0] are the three LSBs of the newest local temperature reading.
Bits [RT2:RT0] are the three LSBs of the newest remote temperature reading.
Local-Temp-DATA-HByte Register (Address 0x0A, Value After Power-On or Reset = 0x80, –128°C)
Bit 7 (MSB)
LT10 (MSB)
Bit 6
LT9
Bit 5
LT8
Bit 4
LT7
Bit 3
LT6
Bit 2
LT5
Bit 1
LT4
Bit 0 (LSB)
LT3
Bits [LT10:LT3] are the eight MSBs of the newest local temperature reading.
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