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Temperature-to-DCY

Adjustment

AMC6821

ActualTemperature

TheDCY-RAMPRegister

determines

thespeedofadjustment.

temperature

PWMControl

Temperature

Channel

AMC6821

SBAS386C – MAY 2006 – REVISED JULY 2007

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.

Figure 27. Auto Fan Temperature Loop

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