ADT7473_11 ONSEMI [ON Semiconductor], ADT7473_11 Datasheet - Page 43

• Manufacturer Part Number: ADT7473_11
• Description: dbCOOL Remote Thermal Monitor and Fan Control
• Manufacturer: ONSEMI [ON Semiconductor]

control allows the ADT7473/ADT7473−1 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 T
control alleviates the need to design for worst−case
conditions and significantly reduces system design and
validation time.
Designing for Worst−Case Conditions
conditions. In PC design, the worst−case conditions include,
but are not limited to, the following:
Worst−Case Altitude
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 feet to 20°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
normally quoted with a tolerance of ±20%. The designer
needs to 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
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, 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.)
GOOD CPU AIRFLOW
System design must always allow for worst−case
A computer can be operated at different altitudes. The
Due to manufacturing tolerances, fan speeds in RPM are
The same motherboard can be used in a number of
GOOD VENTING = GOOD AIR
VENTS
I/O CARDS
VENTS
FAN
EXCHANGE
Figure 64. Chassis Airflow Issues
SUPPLY
POWER
DRIVE
BAYS
CPU
FAN
VENTS
POOR VENTING = POOR AIR
POOR CPU
AIRFLOW
I/O CARDS
EXCHANGE
POWER
SUPPLY
DRIVE
BAYS
FAN
http://onsemi.com
CPU
MIN
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Worst−Case Processor Power Consumption
true 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
peripheral components, again overcooling the system.
Worst−Case Assembly
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 the worst−case conditions.
conditions in all these cases, the actual system is almost
never operated at worst−case conditions. The alternative to
designing for the worst case is to use the dynamic T
control function.
Dynamic T
automatic fan control loop by adjusting the T
based on system performance and measured temperature.
This is important because, instead of designing for the worst
case, the system thermals can be defined as operating zones.
The ADT7473/ADT7473−1 can self−adjust its fan control
loop to maintain either an operating zone temperature or a
system target temperature. For example, it can be specified
that the ambient temperature in a system should be
maintained at 50°C. If the temperature is below 50°C, the
fans might not need to run, or might run very slowly. If the
temperature is higher than 50°C, the fans need to throttle up.
the right settings to suit the system’s fan control solution.
This can involve designing for the worst case, followed by
weeks of system thermal characterization, and finally fan
acoustic optimization (for psycho−acoustic reasons).
INTERFACE
INTEGRATED
This data sheet maximum does not necessarily reflect the
The tendency is to design to data sheet maximums for
Every system is unique because of manufacturing
Although a design usually accounts for worst−case
Dynamic T
The challenge presented by any thermal design is finding
MATERIAL
THERMAL
SPREADER
HEAT
SUBSTRATE
HEAT
SINK
MIN
EPOXY
MIN
Control Overview
Figure 65. Thermal Model
THERMAL INTERFACE MATERIAL
control mode builds on the basic
PROCESSOR
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JTIM
SA
TIMS
CTIM
TIMC
T
T
T
T
T
T
TIM
TIM
A
S
C
J
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CS
MIN
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value
MIN
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