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ADT7467_12 Datasheet, PDF (40/72 Pages) ON Semiconductor – Remote Thermal Monitor and Fan Controller
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ADT7467
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 38. SELECTING A TRANGE VALUE
Bits <7:4> (Note 1)
TRANGE (C)
0000
2
0001
2.5
0010
3.33
0011
4
0100
5
0101
6.67
0110
8
0111
10
1000
13.33
1001
16
1010
20
1011
26.67
1100
32 (default)
1101
40
1110
53.33
1111
80
1. Register 0x5F configures Remote 1 TRANGE.
Register 0x60 configures local TRANGE.
Register 0x61 configures Remote 2 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
(eq. 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) TRANGEń170 (eq. 2)
where:
(Max DC * Min DC)  TRANGE/170 is the effective TRANGE
value.
See the Fan Speed and PWM Duty Cycle section.
Figure 63 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.
100
90
80
70
60
50
40
30
20
10
0
0
100
90
80
70
60
50
40
30
20
10
0
0
2C
2.5C
3.33C
4C
5C
6.67C
8C
10C
13.3C
16C
20C
26.6C
32C
40C
53.3C
20
40
60
80
100 120 80C
TEMPERATURE ABOVE TMIN
2C
2.5C
3.33C
4C
5C
6.67C
8C
10C
13.3C
16C
20C
26.6C
32C
40C
53.3C
20
40
60
80 100 120 80C
TEMPERATURE ABOVE TMIN
Figure 63. TRANGE vs. Fan Speed Profile
The graphs in Figure 63 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 64 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.
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