Analog Devices dBCool ADT7473 Manual page 48

ADT7473
Dynamic T Control Overview
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Dynamic T control mode builds up
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fan control loop by adjusting the T
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 can
self-adjust its fan control loop to
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 challenge presented by any thermal design is finding the
right settings to suit the system's fan cont
involve designing for the worst case, followed by weeks of
system thermal characterization, and finally fan acoustic
optimization (for psycho-acoustic reasons). Getting the most
benefit from the auto matic fan control mode involves character-
izing the system to find the best T
control loop, and the best PWM
speed setting. Using the ADT7473's dynamic T
mode, however, shortens the characterization time and
alleviates tweaking the control loop settings because the de
can self-adjust during system operation.
Dynamic T control mode is operated by specifying th
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operating zone temperatures required for the system.
Associated with this control mode are three operating po
registers, one for each temperature channel. This allows th
system thermal solution to be broken down into distinct
thermal zones. For example, CPU oper
70°C, VRM operating temperatu
operating temperature is 50°C. The ADT7473
alte s the control solution to maintain each zone temperature as r
close ly as possible to its target operating point.
Ope rating Point Registers
Register 0x33, Remote 1 Operating Point = 0xA4
(100°C default)
Regi ster 0x34, Local Temperature Operating Point = 0xA4
(100°C default)
Regi ster 0x35, Remote 2 Operating Point = 0xA4
(100 °C default)
on the basic automatic
value based on system
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maintain either an operating
rol solution. This can
and T settings for the
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value for the quietest fan
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control
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vice
e
int
e
ating temperature is
re is 80°C, and ambient
dynamically
Figure 63 shows an overview of
operation of the dynamic T
,
T T
LOW MIN
Table 15 provides a brief description of each parameter.
Table 15. T
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Parameter
T
LOW
T
HIGH
T
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Oper atin g
Point
T
THERM
T
RANGE
Dynamic T
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Because the dynamic T
the automatic fan control mode, program the automatic fan
control mode parameters first, as described in Step 1: Hardware
Configuration to Step 8: T
proceed with dynamic T
Rev. A | Page 48 of 76
the parameters that affect the
control loop.
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OPERATING T T T
HIGH THERM RANGE
POINT
Figure 63. Dynamic T Control Lo p
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Control Loop Parameters
Description
If the tem erature dr p ops below th
er ror flag is set in a st atus regist
SMB ALER T interrupt can be generated.
If the tem peratur e ex ceeds the
erro r flag is set in a st atus registe
SMBA LER T interrupt can be gene
The temp erature a t w hich the fan turns on
under automatic fan speed contro
The ta rg et temper atu re for a partic
tempe ra ture zone . Th e ADT7473 a
maintain system temperature at about the
operating point by adjusting the T
of the control loop.
If the temperature exceeds this critical limit, the
fans can be run at 100% for maximum cooling.
Programs the PWM duty cycle vs. temperatu
control slope.
Control Programming
control mode is a basic extension of
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for Temperature Channels, then
HYST
control mode programming.
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TEMPERATURE
o
e T limit, an
LO W
er an d an
T limit, an
HIGH
r an d an
rat ed.
l.
u lar
tte mpts to
parameter
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re