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ADM1031ARQZR7

Intelligent Temperature Monitor and Dual PWM Fan Controller

ON Semiconductor 

ADM1031

Table 7. Programming PWM Duty Cycle

Decimal Value

PWM Duty Cycle

00

0%

01

7%

02

14%

03

04

05

06

07

08

09

10 (0×0A)

11 (0×0B)

12 (0×0C)

13 (0×0D)

14 (0×0E)

15 (0×0F)

20%

27%

33% (Default)

40%

47%

53%

60%

67%

73%

80%

87%

93%

100%

The temperature at which the fan runs full−speed (100%

duty cycle) is given by:

TMAX = TMIN + ((Max DC – Min DC) × TRANGE/10)

where:

TMAX = Temperature at which fan runs full−speed.

TMIN = Temperature at which fan turns on.

Max DC = Maximum duty cycle (100%) = 15 decimal.

Min DC = Duty cycle at TMIN, programmed in to fan speed

configuration register (default = 33% = 5 decimal).

TRANGE = PWM duty cycle vs. temperature slope.

Example 1

TMIN = 0°C, TRANGE = 40°C

Min DC = 53% = 8 decimal (Table 7)

Calculate TMAX.

TMAX = TMIN + ((Max DC − Min DC) × TRANGE/10)

TMAX = 0 + ((100% DC − 53% DC) × 40/10)

TMAX = 0 + ((15 − 8) × 4) = 28

TMAX = 28°C (as seen on Slope 2 of Figure 26)

Example 2

TMIN = 0°C, TRANGE = 40°C

Min DC = 73% = 11 decimal (Table 7)

Calculate TMAX.

TMAX = TMIN + ((Max DC – Min DC) × TRANGE/10)

TMAX = 0 + ((100% DC – 73% DC) × 40/10)

TMAX = 0 + ((15 – 11) × 4) = 16

TMAX = 16°C (as seen on Slope 3 of Figure 26)

Example 3

TMIN = 0°C, TRANGE = 40°C

Min DC = 33% = 5 decimal (Table 7)

Calculate TMAX.

TMAX = TMIN + ((Max DC – Min DC) × TRANGE/10)

TMAX = 0 + ((100% DC – 33% DC) × 40/10)

TMAX = 0 + ((15 – 5) × 4) = 40

TMAX = 40°C (as seen on Slope 1 of Figure 26)

In this case, since the minimum duty cycle is the default

33%, the equation for TMAX reduces to:

TMAX = TMIN + ((Max DC – Min DC) × TRANGE/10)

TMAX = TMIN + ((15 – 5) × TRANGE/10)

TMAX = TMIN + (10 × TRANGE/10)

TMAX = TMIN + TRANGE

Relevant Registers for Automatic Fan Speed Control

Mode

Register 0y00 Configuration Register 1

<7> Logic 1 selects automatic fan speed control, Logic 0

selects software control (Default = 1).

<6:5> 00 = Remote Temp 1 controls Fan 1, Remote Temp 2

controls Fan 2.

01 = Remote Temp 1 controls Fan 1 and Fan 2

10 = Remote Temp 2 controls Fan 1 and Fan 2

11 = Fastest Calculated Speed controls Fan 1 and 2

Register 0y20, 0y21 Fan Characteristics Registers 1, 2

<2:0> Fan X Spin−Up Time.

000 = 200 ms

001 = 400 ms

010 = 600 ms

011 = 800 ms

100 = 1 sec

101 = 2 sec (Default)

110 = 4 sec

111 = 8 sec

<5:3> PWM Frequency Driving the Fan.

000 = 11.7 Hz

001 = 15.6 Hz

010 = 23.4 Hz

011 = 31.25 Hz (Default)

100 = 37.5 Hz

101 = 46.9 Hz

110 = 62.5 Hz

111 = 93.5 Hz

<7:6> Speed Range N; defines the lowest fan speed that can

be measured by the device.

00 = 1: Lowest Speed = 2647 RPM

01 = 2: Lowest Speed = 1324 RPM

10 = 4: Lowest Speed = 662 RPM

11 = 8: Lowest Speed = 331 RPM

Register 0y22 Fan Speed Configuration Register

<3:0> Min Speed: This nibble contains the speed at which

the fan runs when the temperature is at TMIN. The default is

0×05, meaning that the fan runs at 33% duty cycle when the

temperature is at TMIN.

<7:4> Min Speed: Determines the minimum PWM cycle for

Fan 2 in automatic fan speed control mode.

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