ADT7467ARQZ-R7 datasheet(33/77 Pages) ONSEMI

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ADT7467

Rev. 3 | Page 33 of 77 | www.onsemi.com

FAN SPEED CONTROL

The ADT7467 controls fan speed using two modes: automatic

and manual.

In automatic fan speed control mode, fan speed is varied with

temperature without CPU intervention once initial parameters

are set up. The advantage of this is that if the system hangs, it is

guaranteed that the system is protected from overheating. The

automatic fan speed control incorporates a feature called

dynamic TMIN calibration. This feature reduces the design effort

required to program the automatic fan speed control loop. For

information on programming the automatic fan speed control

loop and the dynamic TMIN calibration, see the Automatic Fan

Control Overview section.

In manual fan speed control mode, the ADT7467 allows the

duty cycle of any PWM output to be manually adjusted. This

can be useful if the user wants to change fan speed in software

or adjust PWM duty cycle output for test purposes. Bits <7:5>

of Register 0x5C to Register 0x5E (PWM Configuration)

control the behavior of each PWM output.

PWM Configuration Register (0x5C to 0x5E)

<7:5> BHVR

111 = manual mode

In manual fan speed control mode, each PWM output can

be manually updated by writing to Register 0x30 through

Programming the PWM Current Duty Cycle Registers

The PWM current duty cycle registers are 8-bit registers that

allow the PWM duty cycle for each output to be set anywhere

from 0% to 100% in steps of 0.39%.

The value to be programmed into the PWMMIN register is given by

Value (decimal) = PWMMIN/0.39

Example 1: For a PWM duty cycle of 50%,

Value (decimal) = 50/0.39 = 128 (decimal)

Value = 128 (decimal) or 0x80 (hexadecimal)

Example 2: For a PWM duty cycle of 33%,

Value (decimal) = 33/0.39 = 85 (decimal)

Value = 85 (decimal) or 0x54 (hexadecimal)

PWM Current Duty Cycle Registers

By reading the PWMx current duty cycle registers, the user can

keep track of the current duty cycle on each PWM output even

when the fans are running in automatic fan speed control mode

or acoustic enhancement mode. See the Automatic Fan Control

Overview section for details.

ADT7467ARQZ-R7 Datasheet(PDF) 33 Page - ON Semiconductor

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