ADT7476ARQZ-R7 datasheet(41/67 Pages) ONSEMI

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ADT7476

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Selecting TRANGE

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 13. Selecting a TRANGE Value

Bits [7:4] (Note 1)

TRANGE (5C)

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; Register 0x60

configures local TRANGE; Register 0x61 configures Remote 2

TRANGE.

Actual Changes in PWM Output

(Advanced Acoustics Settings)

While the automatic fan control algorithm describes the

general response of the PWM output, it is also necessary to

note that the enhance acoustics registers (0x62 and 0x63)

can be used to set/clamp the maximum rate of change of

PWM output for a given temperature zone. This means that

if TRANGE is programmed with an AFC slope that is quite

steep, a relatively small change in temperature could cause

a large change in PWM output and possibly an audible

change in fan speed, which can be noticeable/ bothersome

to end users.

Decreasing the speed the PWM output changes by

programming the smoothing on the appropriate temperature

channels (Register 0x62 and Register 0x63) changes how

fast the fan speed increases/decreases in the event of a

temperature spike. The PWM duty cycle increases slowly

until the PWM duty cycle reaches the appropriate duty cycle

as defined by the AFC curve.

Figure 61 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.

Figure 61. TRANGE vs. Actual Fan Speed

(Not PWM Drive) Profile

TEMPERATURE ABOVE TMIN

100

120

100

TEMPERATURE ABOVE TMIN

(B)

(A)

100

120

100

25C

805C

53.35C

405C

325C

26.65C

205C

165C

13.35C

105C

85C

6.675C

55C

45C

3.335C

2.55C

25C

805C

53.35C

405C

325C

26.65C

205C

165C

13.35C

105C

85C

6.675C

55C

45C

3.335C

2.55C

The graphs in Figure 61 assume that the fan starts from 0%

PWM duty cycle. Clearly, the minimum PWM duty cycle,

PWMMIN, needs to be factored in to see how the loop

actually performs in the system. Figure 62 shows how

TRANGE is affected when the PWMMIN value is set to 20%.

It can be seen that the fan actually runs at about 45% fan

speed when the temperature exceeds TMIN.

ADT7476ARQZ-R7 Datasheet(PDF) 41 Page - ON Semiconductor

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