ADT7462ACPZ-R7 datasheet(37/81 Pages) ONSEMI

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ADT7462

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The TRANGE or fan control slope is determined by the

following procedure:

1. Determine the maximum operating temperature for

that channel (for example, 70

°C).

2. Determine experimentally 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.)

3. Determine the slope of the required control loop to

meet these requirements.

4. Using the ADT7462 evaluation software, this

functionality can be graphically programmed and

visualized.

Figure 58. Adjusting PWMMIN Affects TRANGE

TMIN

100%

33%

50%

305C

405C

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.

Figure 59. Increasing PWMMIN Changes Effective

TRANGE

TMIN

100%

33%

50%

305C

405C

455C

545C

10%

25%

For a given TRANGE value, the temperature at which the

fan runs at full speed for different PWMMIN values can be

easily calculated by:

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 PWM duty cycle vs. temperature slope.

Example 1

Calculate TMAX, 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)

Example 4

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

and PWMMIN = 50% duty cycle = 128 (decimal).

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

TMAX = 30°C + (100% − 50%) × 40°C/170

TMAX = 30°C + (255 − 128) × 40°C/170

TMAX = 60°C (effective TRANGE = 30°C)

Selecting a TRANGE Slope

The TRANGE value can be selected for each temperature

channel: local, Remote 1, Remote 2, and Remote 3. Bits

[7:4] (RANGE) of Register 0x60 to Register 0x63 define the

TRANGE value for each temperature channel (see Table 81

and Table 82).

Summary of TRANGE Function

When using the automatic fan control function, the

temperature at which the fan reaches full speed can be

calculated by:

TMAX + TMIN ) TRANGE

(eq. 6)

Equation 6 holds true only when PWMMIN is equal to 33%

PWM duty cycle.

Increasing or decreasing PWMMIN changes the effective

TRANGE, although the fan control still follows the same

PWM duty cycle to temperature slope. The effective

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