ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 36

• Manufacturer Part Number: ADT7467
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7467
DYNAMIC T
In addition to the automatic fan speed control mode, the
ADT7467 has a mode that extends the basic automatic fan
speed control loop. Dynamic T
to intelligently adapt the system’s cooling solution to optimize
system performance or system acoustics, depending on user or
design requirements. Use of dynamic T
need to design for worst-case conditions, and it significantly
reduces the time required for system design and validation.
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. The
altitude affects the relative air density, which alters the
effectiveness of the fan cooling solution. For example,
comparing 40°C air temperature at 10,000 ft. to 20°C air
temperature at sea level, relative air density is increased by
40%. This means that at a given temperature the fan can
spin 40% slower and make less noise at sea level than it can
at 10,000 ft.
Worst-Case Fan
Due to manufacturing tolerances, fan speeds in RPM are
normally quoted with a tolerance of ±20%. The designer
should assume that the fan RPM is 20% below tolerance.
This translates to reduced system airflow and elevated
system temperature. Note that a difference of 20 % in the
fans’ tolerance can negatively impact system acoustics,
because the fans 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 thermal characteristics. Moreover,
for a given chassis, the addition of add-in cards, cables, and
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.)
MIN
CONTROL MODE
MIN
control allows the ADT7467
MIN
control alleviates the
Rev. A | Page 36 of 80
•
•
•
Although a design usually accounts for such worst-case
conditions, the system is almost never operated at worst-case
conditions. An alternative to designing for the worst case is to
use the dynamic T
INTERFACE
INTEGRATED
GOOD CPU AIRFLOW
MATERIAL
THERMAL
SPREADER
Worst-Case Processor Power Consumption
Designing for worst-case CPU power consumption can
result in a processor becoming overcooled, generating
excess system noise.
Worst-Case Peripheral Power Consumption
The tendency is to design to data sheet maximums for
peripheral components (again overcooling the system).
Worst-Case Assembly
Every system is unique because of manufacturing
variations. Heat sinks may be loose fitting or slightly
misaligned. Too much or too little thermal grease might be
used, or variations in application pressure for thermal
interface material could affect the efficiency of the thermal
solution. Accounting for manufacturing variations in every
system is difficult; therefore, the system must be designed
for worst-case conditions.
VENTS
I/O CARDS
GOOD AIR EXCHANGE
HEAT
SUBSTRATE
GOOD VENTING =
VENTS
HEAT
FAN
SINK
EPOXY
THERMAL INTERFACE MATERIAL
MIN
Figure 50. Chassis Airflow Issues
SUPPLY
POWER
DRIVE
BAYS
PROCESSOR
CPU
Figure 51. Thermal Model
FAN
control function.
VENTS
POOR CPU
AIRFLOW
I/O CARDS
θ
θ
θ
θ
θ
POOR AIR EXCHANGE
SA
TIMS
CTIM
TIMC
JTIM
POOR VENTING =
T
T
T
T
T
T
TIM
TIM
A
S
C
J
θ
CS
SUPPLY
POWER
θ
DRIVE
BAYS
CA
FAN
CPU
θ
JA