ADT7467ARQZ-R7 datasheet(47/77 Pages) ONSEMI

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ADT7467

Rev. 3 | Page 47 of 77 | www.onsemi.com

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 65. TRANGE and Percentage of Fan Speed Slopes with PWMMIN = 20%

Determining TRANGE for Each Temperature Channel

The following example shows how different TMIN and TRANGE

settings can be applied to three thermal zones. In this example,

the following TRANGE values apply:

TRANGE = 80°C for ambient temperature

TRANGE = 53.3°C for CPU temperature

TRANGE = 40°C for VRM temperature

This example uses the mux configuration described in the

Step 2: Configuring the Mux section, with the ADT7467

connected as shown in Figure 56. Both CPU temperature and

VRM temperature drive the CPU fan connected to PWM1.

Ambient temperature drives the front chassis fan and the rear

chassis fan connected to PWM2 and PWM3. The front chassis

fan is configured to run at PWMMIN = 20%; the rear chassis fan

is configured to run at PWMMIN = 30%. The CPU fan is

configured to run at PWMMIN = 10%.

4-Wire Fans

The control range for 4-wire fans is much wider than that of

2-wire or 3-wire fans. In many cases, 4-wire fans can start with

a PWM drive of as little as 20%.

TEMPERATURE ABOVE TMIN

10203040

100

TEMPERATURE ABOVE TMIN

100

10203040

100

Figure 66. TRANGE and Percentage of Fan Speed Slopes for VRM, Ambient, and

CPU Temperature Channels

STEP 7: T

THERM FOR TEMPERATURE CHANNELS

TTHERM is the absolute maximum temperature allowed on a

temperature channel. Above this temperature, a component

such as the CPU or VRM might be operating beyond its safe

operating limit. When the temperature measured exceeds

TTHERM, all fans are driven at 100% PWM duty cycle (full speed)

to provide critical system cooling.

The fans remain running at 100% until the temperature drops

below TTHERM minus hysteresis, where hysteresis is the number

programmed into the Hysteresis Registers 0x6D and 0x6E. The

default hysteresis value is 4°C.

The TTHERM limit should be considered the maximum worst-case

operating temperature of the system. Because exceeding any

TTHERM limit runs all fans at 100%, it has significant negative

acoustic effects. Ultimately, this limit should be set up as a fail-

safe, and users should ensure that it is not exceeded under

normal system operating conditions.

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