AMC6821-Q1 Datasheet, PDF (27/54 Pages) Texas Instruments – INTELLIGENT TEMPERATURE MONITOR AND PWM FAN CONTROLLER

AMC6821-Q1
www.ti.com ...................................................................................................................................................................................................... SBAS475 – JUNE 2009
Auto Temperature Fan Mode
The Auto Temperature-Fan mode is a closed-loop control that optimizes fan speed for a given temperature to
intelligently manage the system thermals/acoustics. It runs stand-alone even without the intervention of a
controller. The AMC6821 has two auto temperature fan control modes. When the bits [FDRC1:FDRC0] = [10]
(default), the fan is in the Auto Remote Temperature-Fan Speed 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 the monitor starts, 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
PWM Control
AMC6821
Figure 27. Auto Fan Temperature Loop
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): AMC6821-Q1
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