AMC6821-Q1 Datasheet, PDF (28/54 Pages) Texas Instruments – INTELLIGENT TEMPERATURE MONITOR AND PWM FAN CONTROLLER

AMC6821-Q1
SBAS475 – JUNE 2009 ...................................................................................................................................................................................................... www.ti.com
The bits [R-TEMP4:R-TEMP0] of the Remote TEMP-FAN Control Register and the bits [L-TEMP4:L-TEMP0] of
the Local TEMP-FAN Control Register are the low temperature bits that define the low temperature of the control
loops. Bits [SPL2:SPL0] of these registers are the slope bits that define the increment of the duty cycle when the
temprature increases 1°C. The bits [RATE2:RATE0] of the DCY-RAMP Register (bits [4:1], 0x23) specify the
updating rate of the duty cycle in the temp-fan control mode, and the bits [STEP1:STEP0] define how much the
duty cycle is adjusted by each updating. The target duty cycle for temperature T1 and the HIGH-TEMP (high
temperature) can be calculated by Equation 3:
Target DCY at T1 = DCY-LOW-TEMP + (T1 - LOW-TEMP) ´ SLOPE;
(100 - DCY-LOW-TEMP)
HIGH-TEMP = (LOW-TEMP) +
SLOPE
(3)
100%
Temperature-to-DCY Adjustment Range
DCY-LOW-TEMP
(DCY at Low Temperature,
Default is 33%)
DCY increases when the temperature rises.
DCY decreases when the temperature reduces.
RPM = 0
0%
Low-Temp-Limit
LOW-TEMP (Low Temperature)
PSV-Temp
(Passive Cooling Temperature)
Out-of-Range
Actual Temperature
Out-of-Range
Normal Range
Figure 28. Active Control Temperature—PWM Duty Cycle
When the active control temperature is equal to or below the corresponding low temperature, the duty cycle is
equal to the value of the DCY-LOW-TEMP Register and the fan runs at a predefined minimum speed. When the
control temperature is equal to or higher than the corresponding high temperature, the PWM duty cycle is set to
100% and the fan runs at full speed. When the active control temperature is equal to or below the corresponding
value of the PSV-Temp Register (the predefined passive cooling temperature), the fan stops and the PWM duty
cycle is set to 0.
28
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