Analog Devices dBCool ADT7467 Manual page 43

T is implemented as a slope, which means that as PWM
RANGE
is changed, T changes, but the actual slope remains the
RANGE
same. The higher the PWM
MIN
T , that is, the fan reaches full speed (100%) at a lower
RANGE
temperature.
100%
50%
33%
25%
10%
0%
T
MIN
Figure 61. Increasing PWM
For a given T value, the temperature at which the fan runs
RANGE
at full speed for different PWM
calculated:
T = T + (Max DC − Min DC) × T
MAX MIN
where:
T is the temperature at which the fan runs full speed.
MAX
T is the temperature at which the fan turns on.
MIN
Max DC is the maximum duty cycle (100%) = 255 decimal.
Min DC is equal to PWM
MIN
T is the duty PWM duty cycle vs. temperature slope.
RANGE
Example: Calculate T, given that T
and PWM = 10% duty cycle = 26 (decimal).
MIN
T = T + (Max DC − Min DC) × T
MAX MIN
T = 30°C + (100% − 10%) × 40°C/170
MAX
T = 30°C + (255 − 26) × 40°C/170
MAX
T = 84°C (effective T
MAX
Example: Calculate T , given that T
MAX
and PWM = 25% duty cycle = 64 (decimal).
MIN
T = T + (Max DC − Min DC) × T
MAX MIN
T = 30°C + (100% − 25%) × 40°C/170
MAX
T = 30°C + (255 − 64) × 40°C/170
MAX
T = 75°C (effective T
MAX
value, the smaller the effective
30°C
40°C
45°C
54°C
Changes Effective T
MIN RANGE
values can be easily
MIN
/170
RANGE
.
= 30°C, T = 40°C,
MIN RANGE
/170
RANGE
= 54°C)
RANGE
= 30°C, T = 40°C,
MIN RANGE
/170
RANGE
= 45°C)
RANGE
Example: Calculate T
MIN
and PWM = 33% duty cycle = 85 (decimal).
MIN
T = T
MAX MIN
T = 30°C + (100% − 33%) × 40°C/170
MAX
T = 30°C + (255 − 85) × 40°C/170
MAX
T = 70°C (effective T
MAX
Example: Calculate T
and PWM = 50% duty cycle = 128 (decimal).
MIN
T = T
MAX MIN
T = 30°C + (100% − 50%) × 40°C/170
MAX
T = 30°C + (255 − 128) × 40°C/170
MAX
T = 60°C (effective T
MAX
Selecting a T
RANGE
The T value can be selected for each temperature channel:
RANGE
Remote 1, local, and Remote 2 temperature. Bits <7:4> (T
of Registers 0x5F to 0x61 define the T
temperature channel.
Table 13. Selecting a T
1
Bits <7:4>
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
1 Register 0x5F configures Remote 1 T
Register 0x60 configures Local T
Register 0x61 configures Remote 2 T
Summary of T
When using the automatic fan control function, the temperature
at which the fan reaches full speed can be calculated by
T = T
MAX MIN
Equation 1 holds true only when PWM
PWM duty cycle.
Rev. 0| Page 43 of 80
, given that T = 30°C, T
MAX MIN
+ (Max DC − Min DC) × T
= 40°C)
RANGE
, given that T = 30°C, T
MAX MIN
+ (Max DC − Min DC) × T
= 30°C)
RANGE
Slope
value for each
RANGE
Value
RANGE
T (°C)
RANGE
2
2.5
3.33
4
5
6.67
8
10
13.33
16
20
26.67
32 (default)
40
53.33
80
.
RANGE
.
RANGE
.
RANGE
Function
RANGE
+ T
RANGE
is equal to 33%
MIN
ADT7467
= 40°C,
RANGE
/170
RANGE
= 40°C,
RANGE
/170
RANGE
)
RANGE
(1)