ADT7467ARQZ-R7 datasheet(46/77 Pages) ONSEMI

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ADT7467

Rev. 3 | Page 46 of 77 | www.onsemi.com

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:

Remote 1, local, and Remote 2 temperature. Bits <7:4> (TRANGE)

of Register 0x5F to Register 0x61 define the TRANGE value for

each temperature channel.

Table 15. Selecting a TRANGE Value

Bits <7:4>1

TRANGE (°C)

0000

0001

2.5

0010

3.33

0011

0100

0101

6.67

0110

0111

1000

13.33

1001

1010

1011

26.67

1100

32 (default)

1101

1110

53.33

1111

1 Register 0x5F configures Remote 1 TRANGE.

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

(1)

Equation 1 holds true only when PWMMIN is equal to 33%

PWM duty cycle.

Increasing or decreasing PWMMIN changes the effective TRANGE,

but the fan control still follows the same PWM duty cycle to

temperature slope. The effective TRANGE for a PWMMIN value can

be calculated using Equation 2:

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

(2)

where:

(Max DC − Min DC) × TRANGE/170 is the effective TRANGE value.

See the Fan Speed and PWM Duty Cycle section.

Figure 64 shows PWM duty cycle vs. temperature for each

TRANGE setting. The lower graph shows how each TRANGE setting

affects fan speed vs. temperature. As can be seen from the

graph, the effect on fan speed is nonlinear.

TEMPERATURE ABOVE TMIN

100

120

100

TEMPERATURE ABOVE TMIN

20406080

100

120

100

2°C

80°C

53.3°C

40°C

32°C

26.6°C

20°C

16°C

13.3°C

10°C

8°C

6.67°C

5°C

4°C

3.33°C

2.5°C

2°C

80°C

53.3°C

40°C

32°C

26.6°C

20°C

16°C

13.3°C

10°C

8°C

6.67°C

5°C

4°C

3.33°C

2.5°C

Figure 64. TRANGE vs. Fan Speed Profile

The graphs in Figure 64 assume that the fan starts from 0% PWM

duty cycle. The minimum PWM duty cycle, PWMMIN, must be

factored in to determine how the loop performs in the system.

Figure 65 shows how TRANGE is affected when the PWMMIN value

is set to 20%. It can be seen that the fan runs at about 45% fan

speed when the temperature exceeds TMIN.

ADT7467ARQZ-R7 Datasheet(PDF) 46 Page - ON Semiconductor

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