ADT7467ARQZ-R7 datasheet(45/77 Pages) ONSEMI

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ADT7467

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STEP 6: TRANGE FOR TEMPERATURE CHANNELS

TRANGE is the range of temperature over which automatic fan

control occurs once the programmed TMIN temperature has

been exceeded. TRANGE is a temperature slope, not an arbitrary

value, that is, a TRANGE of 40°C holds true only for PWMMIN =

33%. If PWMMIN is increased or decreased, the effective TRANGE

changes.

TEMPERATURE

TMIN

100%

PWMMIN

TRANGE

Figure 61. TRANGE Parameter Affects Cooling Slope

The TRANGE or fan control slope is determined by the following

procedure:

Determine the maximum operating temperature for that

channel (for example, 70°C).

Through experimentation, determine the fan speed (PWM

duty cycle value) that does not exceed the temperature at

the worst-case operating points. (For example, 70°C is

reached when the fans are running at 50% PWM duty

cycle.)

Determine the slope of the required control loop to meet

these requirements.

The ADT7467 evaluation software can graphically

program and visualize this functionality. Ask your local

Analog Devices sales representative for details.

TMIN

100%

33%

50%

30°C

40°C

Figure 62. Adjusting PWMMIN Affects TRANGE

TRANGE is implemented as a slope, which means that as PWMMIN

is changed, TRANGE changes, but the actual slope remains the

same. The higher the PWMMIN value, the smaller the effective

TRANGE, that is, the fan reaches full speed (100%) at a lower

temperature.

TMIN

100%

33%

50%

30°C

40°C

25%

10%

45°C

54°C

Figure 63. Increasing PWMMIN Changes Effective TRANGE

For a given TRANGE value, the temperature at which the fan runs

at full speed, which varies with the PWMMIN value, can be easily

calculated.

TMAX = TMIN + (Max DC − Min DC) × TRANGE /170

where:

TMAX is the temperature at which the fan runs full speed.

TMIN is the temperature at which the fan turns on.

Max DC is the maximum duty cycle (100%) = 255 decimal.

Min DC is equal to PWMMIN.

TRANGE is the duty PWM duty cycle vs. temperature slope.

Example 1: Calculate T, given that TMIN = 30°C, TRANGE = 40°C,

and PWMMIN = 10% duty cycle = 26 (decimal).

TMAX = TMIN + (Max DC − Min DC) × TRANGE /170

TMAX = 30°C + (100% − 10%) × 40°C/170

TMAX = 30°C + (255 − 26) × 40°C/170

TMAX = 84°C (Effective TRANGE = 54°C)

Example 2: Calculate TMAX, given that TMIN = 30°C, TRANGE = 40°C,

and PWMMIN = 25% duty cycle = 64 (decimal).

TMAX = TMIN + (Max DC − Min DC) × TRANGE /170

TMAX = 30°C + (100% − 25%) × 40°C/170

TMAX = 30°C + (255 − 64) × 40°C/170

TMAX = 75°C (Effective TRANGE = 45°C)

Example 3: Calculate TMAX, given that TMIN = 30°C, TRANGE = 40°C,

and PWMMIN = 33% duty cycle = 85 (decimal).

TMAX = TMIN + (Max DC − Min DC) × TRANGE /170

TMAX = 30°C + (100% − 33%) × 40°C/170

TMAX = 30°C + (255 − 85) × 40°C/170

TMAX = 70°C (Effective TRANGE = 40°C)

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