AMC6821 Datasheet, PDF (23/47 Pages) Burr-Brown (TI) – Analog Monitor and Control Circuit

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AMC6821
SBAS386A – MAY 2006 – REVISED MAY 2006
Measure RPM and adjust DCY once every second (TACH-FAST = 0)
or once every 250ms (TACH-FAST = 1).
(TACH-DATA Register) - TACH-SETTING Register)
No
|Error| > 0x000A
Yes
(TACH-DATA) >
(TACH-SETTING)
Yes
Increase DCY
by one STEP
No
Decrease DCY
by one STEP
Figure 17. RPM Fan DCY Loop
Auto Temperature Fan Mode
The AMC6821 has two auto temperature fan control modes. When the bits [FDRC1:FDRC0] = [10] (default), the
fan is in the auto remote fan temperature control mode. The temperature reading from the remote temperature
sensor is the active control temperature that controls the PWM duty cycle. When the bits [FDRC1:FDRC0] =
[11], the fan is in the maximum fast-speed calculated control mode.
The local temperature and the remote temperature have independently-programmed control loops with different
parameters. In the maximum fast-speed calculated control mode, the required fan speed is calculated for the
remote and local channels, respectively. Whichever control loop calculates the fastest speed based on the
measured temperature drives the fan. After start-up, the PWM duty cycle is determined by the actual control
temperature. When the temperature is above the low temperature and below the high temperature, the internal
control loop automatically adjusts the duty cycle to a proper value according to the measured temperature.
When the temperature rises, the duty cycle increases to a higher value; when the temperature drops, the duty
cycle reduces. This architecture makes the fan always run at an optimal speed. This adjustment is based on the
control-loop parameters defined in the Local TEMP-FAN Control Register, Remote TEMP-FAN Control Register,
and the DCY-RAMP Register. Changing the parameters changes the desired value of the duty cycle and the fan
speed.
+V
The DCY-RAMP Register temperature determines
the speed of adjustment.
Temperature-to-DCY ^{Actual Temperature} Temperature
Adjustment
Channel
AMC6821
PWM Control
Figure 18. Auto Fan Temperature Loop
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