ADT7462ACPZ-R7 datasheet(40/81 Pages) ONSEMI

40 / 81 page

ADT7462

http://onsemi.com

Figure 63. How TTHERM Relates to Automatic Fan

Control

TMIN

100%

TTHERM

TRANGE

HYSTERESIS

Step 7—THYST for Temperature Channels

THYST is the amount of extra cooling a fan provides after

the temperature measured has dropped back below TMIN

before the fan turns off. The premise for temperature

hysteresis (THYST) is that without it, the fan would merely

chatter or cycle on and off regularly whenever the

temperature hovers near the TMIN setting.

The THYST value chosen determines the amount of time

needed for the system to cool down or heat up as the fan is

turning on and off. Values of hysteresis are programmable in

the range of 1

°C to 15°C. Larger values of THYST prevent the

fans from chattering on and off. The THYST default value is

set at 4

°C.

Hysteresis Register

In some applications, it is required that fans not turn off

below TMIN but remain running at PWMMIN. Bits [1:0] of

the PWM1, PWM2 Frequency Register (0x25) and the

PWM3, PWM4 Frequency Register (0x26) allow the fans to

be turned off or to be kept spinning below TMIN. If the fans

are always on, the THYST value has no effect on the fan when

the temperature drops below TMIN.

Figure 64. THYST Value Applies to Fan On/Off

Hysteresis

TMIN

100%

TRANGE

TTHERM

THYST

Dynamic TMIN Control Mode

In addition to the automatic fan speed control mode

described in the Automatic Fan Control Overview section,

the ADT7462 has a mode that extends the basic automatic

fan speed control loop. Dynamic TMIN control allows the

ADT7462 to intelligently adapt the system’s cooling

solution for best system performance or lowest possible

system acoustics, depending on user or design requirements.

Use of dynamic TMIN control alleviates the need to design

for worst−case conditions and significantly reduces system

design and validation time.

Designing for Worst−Case Conditions

System design must always allow for worst−case

conditions. In PC design, the worst−case conditions include,

but are not limited to, the following:

• Worst−Case Altitude

A computer can be operated at different altitudes.

Altitude affects the relative air density, which alters the

effectiveness of the fan cooling solution. For example,

when comparing 40

°C air temperature at 10,000 feet to

°C air temperature at sea level, relative air density is

increased by 40%. This means that the fan can spin

40% slower and make less noise at sea level than at

10,000 feet while keeping the system at the same

temperature at both locations.

• Worst−Case Fan

Due to manufacturing tolerances, fan speeds in rpm are

normally quoted with a tolerance of

±20%. The

designer must assume that the fan rpm can be 20%

below tolerance. This translates to reduced system

airflow and elevated system temperature. Note that fans

20% out of tolerance can negatively impact system

acoustics because they run faster and generate more

noise.

• Worst−Case Chassis Airflow

The same motherboard can be used in a number of

different chassis configurations. The design of the

chassis and the physical location of fans and

components determine the system’s thermal

characteristics. Moreover, for a given chassis, the

addition of add−in cards, cables, or other system

configuration options can alter the system airflow and

reduce the effectiveness of the system cooling solution.

The cooling solution can also be inadvertently altered

by the end user. (For example, placing a computer

against a wall can block the air ducts and reduce system

airflow.)

ADT7462ACPZ-R7 数据表(PDF) 40 Page - ON Semiconductor

ADT7462ACPZ-R7 数据表(HTML) 40 Page - ON Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

数据表下载