Programming the Automatic Fan Speed Control Loop

AN-613
APPLICATIONAN-613
NOTE
APPLICATIONAN-613
NOTE
APPLICATIONAN-613
NOTE
APPLICATION NOTE
Programming the Automatic Fan Speed Control Loop
a
a
a
a
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel: 781/329-4700 • Fax: 781/326-8703 • www.analog.com
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel: 781/329-4700 • Fax: 781/326-8703 • www.analog.com
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel: 781/329-4700 • Fax: 781/326-8703 • www.analog.com
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106 • Tel: 781/329-4700 • Fax: 781/326-8703 • www.analog.com
Programming the Automatic
Fan Speed Control Loop
By Mary Burke
By Mary Burke
Programming the Automatic
Fan Speed Control Loop
By Mary Burke
temperature
and thus
for a given fan are critical
AUTOMATIC FAN SPEED
CONTROL
Programming
the Automatic
Fan
Speedchannel
Control
Loop
since
these
define
the
thermal
characteristics
sysThe
ADT7460/ADT7463
have
a
local
temperature
sensor
temperature channel and thus for a given fan of
arethe
critical
AUTOMATIC FAN SPEED CONTROL
By Mary Burke
tem.
The
thermal
validation
of
the
system
is
one
of
the
and
two
remote
temperature
channels
that
may
be
consince these define the thermal characteristics of the sysThe ADT7460/ADT7463 have a local temperature sensor
most
important
steps
of
the
design
process,
so
these
nected
to
an
on-chip
diode-connected
transistor
on
a
tem.
The thermal
validation
offor
thea system
is are
onecritical
of the
and
two remote
channels that may be contemperature
channel
and thus
given fan
AUTOMATIC
FANtemperature
SPEED CONTROL
values
should
be steps
carefully
selected.
CPU.
These
three
temperature
may
be used
most
important
of the
design
process,ofso
nected
to an
on-chip
diode-connected
transistor
onasa
since these
define
the thermal
characteristics
thethese
sysThe ADT7460/ADT7463
have a channels
local temperature
sensor
the
basis
forthree
automatic
fan
speed
control
to
drive
temperature
channel
and thus
given fan
AUTOMATIC
FAN
SPEED
CONTROL
values
should
be carefully
selected.
CPU.
These
temperature
channels
may
be
used
as
tem.
The
thermal
validation
offor
thea system
is are
onecritical
of the
and
two
remote
temperature
channels
that
may
be fans
conusing
pulsewidth
modulation
(PWM).
In
general,
thea
AIM
THISdefine
SECTION
sinceOF
these
the thermal
characteristics
thethese
sysThe basis
ADT7460/ADT7463
have
a local
temperature
sensor
the
fan speed
control
to
drive
fans
most
important
steps
of the design
process,ofso
nected
to for
an automatic
on-chip
diode-connected
transistor
on
greater
the
number
of
fans
in
a
system,
the
better
the
The
aim
of
this
note
is system
not only
provide
tem. OF
The
thermal
validation
of the
is to
one
of the
and two
remote
channels
may
be conusing
pulsewidth
modulation
(PWM).that
In
general,
the
values
should
beapplication
carefully
selected.
CPU.
These
threetemperature
temperature
channels
may
be used
as
AIM
THIS
SECTION
cooling,
but
this
is toof
the
detriment
of system
the
system
with
understanding
automost
important
steps
of an
thenote
design
process,
so
these
nected
to
an
on-chip
diode-connected
transistor
a
greater
the
number
fans
in a system,
the
betteron
the
the
basis
for
automatic
fan
speed
control
to acoustics.
drive
fans
The
aim
of designer
this application
is not
onlyoftothe
provide
Automatic
fan
speed
control
reduces
acoustic
noise
matic
fan
control
loop,
but
to
also
provide
step-by-step
values
be carefully
selected.
CPU. These
channels
may
be
usedthe
as
cooling,
but three
this istemperature
to
the detriment
of system
acoustics.
using
pulsewidth
modulation
(PWM).
In
general,
the
system
with an
understanding of the autoAIM
OFshould
THISdesigner
SECTION
by
fan
speed
according
to measured
temguidance
as
to how
tobut
most
effectively
evaluate
and
the optimizing
basis
for
automatic
fan
speed
control
to drive
fans
Automatic
fan
speed
acoustic
noise
greater
the
number
of control
fans
in areduces
system,
the
better
the
matic
fanof
control
loop,
to
also
step-by-step
The aim
this
application
note
isprovide
not only
to provide
perature.
Reducing
fan
speed
can
also
decrease
system
select
the
critical
system
parameters.
To
optimize
the
using
pulsewidth
modulation
(PWM).
In general,
the
AIMsystem
OF THIS
SECTION
by
optimizing
speed
according
measured
temcooling,
but thisfan
is to
the detriment
ofto
system
acoustics.
guidance
asdesigner
to howwith
to most
effectively evaluate
and
the
an understanding
of the autocurrent
consumption.
The
automatic
fan
speed
control
system
characteristics,
the
designer
needs
to
give
some
greater the
number
of control
fans
areduces
system,
the better
the
The aim
this application
note
not To
only
to provide
perature.
Reducing
fan
speedincan
also decrease
system
Automatic
fan
speed
acoustic
noise
select
theof
critical
system
optimize
the
matic
fan
control
loop,
butparameters.
to
alsoisprovide
step-by-step
mode
is consumption.
very
flexible
owing
to the number
of acoustics.
programforethought
totohow
system
will needs
be configured,
i.e.,
cooling,
but this
is to
the
detriment
ofto
system
the system
with
an
understanding
the some
autocurrent
The
automatic
fan
speed
control
by
optimizing
fan
speed
according
measured
temsystem
characteristics,
designer
toofgive
guidance
asdesigner
howthe
tothe
most
effectively
evaluate
and
mable
including
TMIN
the
number
of
where
they
are
located,
and what
and
TRANGE
, as
Automatic
fanflexible
speed
control
reduces
acoustic
noise
matic
fan
loop,
but
to
also
provide
step-by-step
mode
isparameters,
very
owing
the
number
of
programperature.
Reducing
fan
speedtocan
also
decrease
system
forethought
to fans,
how
the
system
will
be
configured,
i.e.,
select
the control
critical
system
parameters.
To
optimize
the
temperatures
are
being
measured
in
the
particular
discussed
in
detail
later.
The
T
and
T
values
for
a
MIN
RANGE
by optimizing
fan speed
measured
guidance
as of
tofans,
how where
tothe
most
effectively
evaluate
and
mable
parameters,
including
T to
current
consumption.
Theaccording
automatic
fan
speed
the
number
they
areneeds
located,
and some
what
system
characteristics,
designer
to give
and
T control
,temas
MIN
RANGE
perature.
Reducing
fan
speed
can
also
decrease
system
mode
is very
flexible
owing
the
number
of
programdiscussed
in detail
later.
The to
TMIN
and
TRANGE
values
for a
current consumption.
The automatic
control
mable
parameters, including
TMIN fan
andspeed
TRANGE
, as
mode is very
flexible
owing
the
number
programTHERMAL
CALIBRATION
discussed
in detail
later.
The to
TMIN
and
TRANGEof
values
for a
100%
mable parameters, including
T
and
T
,
as
MIN
RANGE
THERMAL CALIBRATION
discussed in detail later. The TMIN and TRANGE100%
values for a
THERMAL CALIBRATION
THERMAL CALIBRATION
REMOTE 1
TEMP
REMOTE 1
TEMP
REMOTE 1
TEMP
REMOTE 1
TEMP
TMIN
TRANGE
TMIN
TRANGE
THERMAL CALIBRATION
THERMAL CALIBRATION
TMIN
TRANGE
THERMAL CALIBRATION
TMIN
TRANGE
LOCAL
TEMP
LOCAL
TEMP
LOCAL
TEMP
LOCAL
TEMP
TMIN
TRANGE
TMIN
TRANGE
THERMAL CALIBRATION
THERMAL CALIBRATION
TMIN
TRANGE
THERMAL CALIBRATION
TMIN
TRANGE
THERMAL CALIBRATION
REMOTE 2
TEMP
REMOTE 2
TEMP
REV. 0
REV. 0
REMOTE 2
TEMP
REMOTE 2
TEMP
TMIN
TMIN
TMIN
TMIN
©20080SCILLC. All rights reserved.
REV.
April 2008 - Rev. 1
REV. 0
100%
PWM
MIN
0%
100%
PWM
MIN
TRANGE
TRANGE
Figure
TRANGE
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PWM
MIN
100%
0%
100%
0%
100%
THERMAL CALIBRATION
select the critical
system
parameters.
optimize
the
temperatures
being
measured
the
particular
forethought
to are
how
the system
will beinTo
configured,
i.e.,
system
characteristics,
the designer
to give
the
number
of fans, where
they areneeds
located,
and some
what
forethought
to are
howbeing
the system
i.e.,
temperatures
measured
inconfigured,
the particular
PWM will be
PWM
theMIN
number of fans, where CONFIG
they are located, and what
PWM
PWM
temperatures
are being measured
in the particular
CONFIG
MIN
RAMP
PWM
CONTROL
PWM1
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GENERATOR
(ACOUSTIC
0%
100%
PWM
MIN
MUX
MUX
MUX
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Automatic Fan Control Block
RAMP
ENHANCEMENT
CONTROL
(ACOUSTIC
ENHANCEMENT
RAMP
TACHOMETER
CONTROL 1
MEASUREMENT
(ACOUSTIC
ENHANCEMENT
TACHOMETER
1
RAMP
MEASUREMENT
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER
1
MEASUREMENT
RAMP
CONTROL
TACHOMETER
1
(ACOUSTIC
RAMP
MEASUREMENT
ENHANCEMENT
CONTROL
(ACOUSTIC
ENHANCEMENT
RAMP
TACHOMETER
CONTROL 2
MEASUREMENT
(ACOUSTIC
ENHANCEMENT
TACHOMETER
2
RAMP
MEASUREMENT
CONTROL
(ACOUSTIC
ENHANCEMENT
TACHOMETER
2
MEASUREMENT
RAMP
CONTROL
TACHOMETER
2
(ACOUSTIC
RAMP
MEASUREMENT
ENHANCEMENT
CONTROL
(ACOUSTIC
ENHANCEMENT
RAMP
TACHOMETER
3
CONTROL
AND 4
(ACOUSTIC
MEASUREMENT
TACHOMETER
3
ENHANCEMENT
RAMP
AND
4
CONTROL
MEASUREMENT
(ACOUSTIC
TACHOMETER
3
ENHANCEMENT
Diagram
AND 4
MEASUREMENT
PWM
PWM
CONFIG
GENERATOR
PWM
CONFIG
PWM
GENERATOR
PWM1
PWM1
PWM
PWM
GENERATOR
CONFIG
PWM1
PWM
CONFIG
PWM
GENERATOR
PWM
PWM
CONFIG
GENERATOR
PWM2
PWM
CONFIG
PWM
GENERATOR
PWM
PWM
GENERATOR
CONFIG
PWM
CONFIG
PWM
GENERATOR
PWM
PWM2
PWM2
PWM2
PWM3
PWM
CONFIG
GENERATOR
PWM3
PWM
CONFIG
PWM
GENERATOR
PWM3
PWM
GENERATOR
PWM3
Figure 1.
Automatic Fan Control Block Diagram
TACHOMETER 3
0%
TRANGE
AND 4
MEASUREMENT
Figure 1. Automatic Fan Control Block Diagram
Figure 1. Automatic Fan Control Block Diagram
Publication Order Number:
AN613/D
AN-613
AN-613
system. The mechanical or thermal engineer who is
addressed early in the design stages. Decisions about
how these capabilities are used should involve the system thermal/mechanical
engineer.
Ask
the following
addressed
early in the design
stages.
Decisions
about
questions:
how
these capabilities are used should involve the sys-
tasked with the actual system evaluation should also be
involved The
at themechanical
beginning of
process.
system.
or the
thermal
engineer who is
tasked with the actual system evaluation should also be
AUTOMATIC
FAN
CONTROL
involved at the
beginning
ofOVERVIEW
the process.
Figure 1 gives a top-level overview of the automatic fan
control circuitry
the ADT7460/ADT7463.
From a sysAUTOMATIC
FANon
CONTROL
OVERVIEW
tems level
perspective,
upoverview
to three system
temperatures
Figure
1 gives
a top-level
of the automatic
fan
can be monitored
to control threeFrom
PWM
outcontrol
circuitry onand
the used
ADT7460/ADT7463.
a sysputs. level
The three
PWM outputs
can be
used temperatures
to control up
tems
perspective,
up to three
system
to four
The ADT7460/ADT7463
allow
thePWM
speed
of
can
be fans.
monitored
and used to control
three
outfour fans
to be PWM
monitored.
temperature
channel
puts.
The three
outputsEach
can be
used to control
up
hasfour
a fans.
thermal
calibration block. allow
This the
allows
to
The ADT7460/ADT7463
speedthe
of
designer
configure
thermal characterfour
fanstotoindividually
be monitored.
Each the
temperature
channel
istics aof thermal
each temperature
has
calibrationchannel.
block. For
Thisexample,
allows one
the
may decide
to run the CPU
fan when
CPU temperature
designer
to individually
configure
the thermal
characterincreases
above
60°C, and achannel.
chassis fan
the local
istics
of each
temperature
For when
example,
one
temperature
above
that at this
may
decide toincreases
run the CPU
fan 45°C.
when Note
CPU temperature
stage,
youabove
have not
assigned
these thermal
calibration
increases
60°C,
and a chassis
fan when
the local
settings
to a increases
particular above
fan drive
(PWM)
temperature
45°C.
Notechannel.
that at The
this
right side
the Block
Diagram these
(Figure
1) shows
controls
stage,
youofhave
not assigned
thermal
calibration
that are fan-specific.
The fan
designer
individual
control
settings
to a particular
drive has
(PWM)
channel.
The
over parameters
suchDiagram
as minimum
PWM
duty cycle,
fan
right
side of the Block
(Figure
1) shows
controls
speed
thresholds,
and evenhas
ramp
controlcontrol
of the
that
arefailure
fan-specific.
The designer
individual
PWMparameters
outputs. This
ultimately
allows
graceful
speed
over
such
as minimum
PWM
duty fan
cycle,
fan
changes
that are
less perceptible
to ramp
the system
user.
speed
failure
thresholds,
and even
control
of the
tem
thermal/mechanical
engineer.
Ask will
the be
following
1. What
ADT7460/ADT7463
functionality
used?
questions:
• PWM2 or SMBALERT?
1. What
ADT7460/ADT7463
functionality
will be used?
• 2.5 V
voltage monitoring
or SMBALERT?
• 2.5
V voltage
monitoring or processor power
PWM2
or SMBALERT?
monitoring?
• 2.5
V voltage monitoring or SMBALERT?
TACH4
fan speed
measurement
or over• 2.5
V voltage
monitoring
or processor
power
temperature THERM function?
monitoring?
5 V voltage
monitoring
or overtemperature
• TACH4
fan speed
measurement
or overTHERM function?
temperature
THERM function?
12VVvoltage
voltagemonitoring
monitoringororovertemperature
VID5 input?
• 5
THERM
function?
The
ADT7460/ADT7463
offers multifunctional pins that
•can
12be
V voltage
monitoring
VID5 input?
reconfigured
to suitor
different
system requirements
and
physical
layouts.
These
multifunction
The ADT7460/ADT7463 offers multifunctional pins pins
that
are
programmable.
Varioussystem
pinout requireoptions
can software
be reconfigured
to suit different
are
discussed
in a separate
note.
ments
and physical
layouts.application
These multifunction
pins
are software
programmable.
Various
pinout three
options
2. How
many fans
will be supported
in system,
or
are
discussed
in
a
separate
application
note.
four? This will influence the choice of whether to use
the TACH4
pin will
or to
for the three
THERM
2. How
many fans
bereconfigure
supported init system,
or
function.
four? This will influence the choice of whether to use
thethe
TACH4
pin to
or be
to controlled
reconfigure
it forthe
the
THERM
3. Is
CPU fan
using
ADT7460/
function.
ADT7463 or will it run at full speed 100% of the time?
PWM outputs. This ultimately allows graceful fan speed
STEP 1: DETERMINING
THE HARDWARE
changes
that are less perceptible
to theCONFIGURATION
system user.
During system design, the motherboard sensing and
control
capabilities should
not be an CONFIGURATION
afterthought, but
STEP
1: DETERMINING
THE HARDWARE
3. Is
the at
CPU
fan it
towill
be free
controlled
usingoutput,
the ADT7460/
If run
100%,
up a PWM
but the
ADT7463
or
will
it
run
at
full
speed
100%
of the time?
system will be louder.
If run at 100%, it will free up a PWM output, but the
system will be louder.
During system design, the motherboard sensing and
control capabilities should not be an afterthought, but
100%
PWM
MIN
100%
PWM
MIN
THERMAL CALIBRATION
THERMAL CALIBRATION
REMOTE 1 =
AMBIENT TEMP
REMOTE 1 =
AMBIENT TEMP
TMIN
0%
TRANGE
THERMAL CALIBRATION
TRANGE
TMIN
100%
LOCAL =
VRM TEMP
LOCAL =
VRM TEMP
TMIN
TRANGE
0%
REMOTE 2 =
CPU TEMP
REMOTE 2 =
CPU TEMP
MUX
PWM
MIN
MUX
THERMAL CALIBRATION
0%
TMIN
TRANGE100%
PWM
MIN
THERMAL CALIBRATION
PWM
MIN
100%
TMIN
TRANGE
TMIN
TRANGE
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
PWM
GENERATOR
CONFIG
RAMP CONTROL
(ACOUSTIC 1
TACHOMETER
ENHANCEMENT)
MEASUREMENT
PWM
GENERATOR
PWM1
TACH1
TACH1
PWM
PWM
GENERATOR
CONFIG
PWM2
RAMP CONTROL
(ACOUSTIC 2
TACHOMETER
ENHANCEMENT)
MEASUREMENT
PWM
GENERATOR
PWM2
TACH2
PWM
CONFIG
TACH2
PWM
PWM
GENERATOR
CONFIG
PWM3
PWM
GENERATOR
PWM3
TACH3
TACHOMETER 2
MEASUREMENT
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 3
AND 4
MEASUREMENT
0%
CPU
FAN SINK
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
RAMP CONTROL
TACHOMETER
(ACOUSTIC 3
AND 4
ENHANCEMENT)
MEASUREMENT
0%
PWM1
PWM
CONFIG
PWM TACHOMETER 1
MIN MEASUREMENT
0%
100%
THERMAL CALIBRATION
PWM
CONFIG
TACH3
CPU
FAN SINK
FRONT
CHASSIS
FRONT
CHASSIS
REAR
CHASSIS
REAR
CHASSIS
Figure 2. Hardware Configuration Example
–2–
1 | Page 2 of 27 | www.onsemi.com
Figure 2.Rev.
Hardware
Configuration Example
REV. 0
–2–
REV. 0
AN-613
FRONT
CHASSIS
FAN
TACH2
PWM1
TACH1
PWM3
REAR
CHASSIS
FAN
5(VRM9)/6(VRM10)
VID[0:4]/VID[0.5]
TACH3
D2+
D2–
THERM
AMBIENT
TEMPERATURE
PROCHOT
D1+
D1–
ADT7463
3.3VSB
5V
12V/VID5
SDA
ADP316x
VRM
CONTROLLER
SCL
VCOMP
SMBALERT
CURRENT
VCORE
GND
Figure 3. Recommended Implementation 1
4. Where will the ADT7460/ADT7463 be physically
located in the system?
This influences the assignment of the temperature
measurement channels to particular system thermal
zones. For example, locating the ADT7460/ADT7463
close to the VRM controller circuitry allows the VRM
temperature to be monitored using the local temperature channel.
Six VID Inputs (VID0 to VID5) for VRM10 Support.
2.
Two PWM Outputs for Fan Control of up to Three
Fans. (The front and rear chassis fans are connected
in parallel.)
3.
Three TACH Fan Speed Measurement Inputs.
4.
VCC Measured Internally through Pin 4.
5.
CPU Core Voltage Measurement (VCORE).
2.5 V Measurement Input Used to Monitor CPU Current (connected to VCOMP output of ADP316x VRM
controller). This is used to determine CPU power
consumption.
7.
5 V Measurement Input.
8.
VRM temperature uses local temperature sensor.
9.
CPU Temperature Measured Using Remote 1 Temperature Channel.
10. Ambient Temperature Measured through Remote 2
Temperature Channel.
RECOMMENDED IMPLEMENTATION 1
Configuring the ADT7460/ADT7463 as in Figure 3 provides the systems designer with the following features:
1.
6.
11. If not using VID5, this pin can be reconfigured as the
12 V monitoring input.
12. Bidirectional THERM Pin. Allows monitoring of
PROCHOT output from Intel® P4 processor, for
example, or can be used as an overtemperature
THERM output.
13. SMBALERT System Interrupt Output.
Rev. 1 | Page 3 of 27 | www.onsemi.com
REV. 0
–3–
AN-613
FRONT
CHASSIS
FAN
TACH2
PWM1
PWM2
TACH1
PWM3
REAR
CHASSIS
FAN
VID[0:4]/VID[0.5]
5(VRM9)/6(VRM10)
TACH3
D2+
D2–
THERM
AMBIENT
TEMPERATURE
PROCHOT
D1+
D1–
ADT7463
3.3VSB
5V
12V/VID5
SDA
ADP316x
VRM
CONTROLLER
SCL
VCOMP
CURRENT
VCORE
GND
Figure 4. Recommended Implementation 2
RECOMMENDED IMPLEMENTATION 2
Configuring the ADT7460/ADT7463 as in Figure 4 provides the systems designer with the following features:
1.
Six VID Inputs (VID0 to VID5) for VRM10 Support.
2.
Three PWM Outputs for Fan Control of up to Three
Fans. (All three fans can be individually controlled.)
3.
Three TACH Fan Speed Measurement Inputs.
4.
VCC Measured Internally through Pin 4.
5.
CPU Core Voltage Measurement (VCORE).
6.
2.5 V Measurement Input Used to Monitor CPU Current (connected to VCOMP output of ADP316x VRM
Controller). This is used to determine CPU power
consumption.
7.
5 V Measurement Input.
8.
VRM Temperature Uses Local Temperature Sensor.
9.
CPU Temperature Measured Using Remote 1 Temperature Channel.
10. Ambient Temperature Measured through Remote 2
Temperature Channel.
11. If not using VID5, this pin can be reconfigured as the
12 V monitoring input.
12. BIDIRECTIONAL THERM Pin. Allows monitoring
of PROCHOT output from Intel P4 processor, for
example, or can be used as an overtemperature
THERM output.
Rev. 1 | Page 4 of 27 | www.onsemi.com
–4–
REV. 0
AN-613
STEP 2: CONFIGURING THE MUX—WHICH
TEMPERATURE CONTROLS WHICH FAN?
After the system hardware configuration is determined,
the fans can be assigned to particular temperature channels. Not only can fans be assigned to individual
channels, but the behavior of fans is also configurable.
For example, fans can be run under automatic fan control, can run manually (under software control), or can
run at the fastest speed calculated by multiple temperature channels. The MUX is the bridge between
temperature measurement channels and the three PWM
outputs.
AUTOMATIC FAN CONTROL MUX OPTIONS
<7:5> (BHVR) REGISTERS 0x5C, 0x5D, 0x5E
000 = Remote 1 Temp controls PWMx
001 = Local Temp controls PWMx
010 = Remote 2 Temp controls PWMx
101 = Fastest Speed calculated by Local and Remote 2
Temp controls PWMx
110 = Fastest Speed calculated by all three temperature
channels controls PWMx
The "Fastest Speed Calculated" options pertain to the
ability to control one PWM output based on multiple
temperature channels. The thermal characteristics of
the three temperature zones can be set to drive a
single fan. An example would be if the fan turns on
when Remote 1 temperature exceeds 60°C or if the local
temperature exceeds 45°C.
Bits <7:5> (BHVR bits) of registers 0x5C, 0x5D, and 0x5E
(PWM configuration registers) control the behavior of
the fans connected to the PWM1, PWM2, and PWM3 outputs. The values selected for these bits determine how
the MUX connects a temperature measurement channel
to a PWM output.
OTHER MUX OPTIONS
<7:5> (BHVR) REGISTERS 0x5C, 0x5D, 0x5E
011 = PWMx runs full speed (default)
100 = PWMx disabled
111 = Manual Mode. PWMx is run under software control.
In this mode, PWM duty cycle registers (registers 0x30 to
0x32) are writable and control the PWM outputs.
MUX
THERMAL CALIBRATION
PWM
CONFIG
PWM
MIN
100%
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
REMOTE 1 =
AMBIENT TEMP
TMIN
TRANGE
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
MUX
TMIN
TRANGE
0%
THERMAL CALIBRATION
100%
TMIN
TRANGE
PWM
GENERATOR
TACHOMETER 2
MEASUREMENT
PWM
MIN
PWM
GENERATOR
Figure 5. Assigning Temperature Channels to Fan Channels
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–5–
FRONT
CHASSIS
TACH2
TACHOMETER 3
AND 4
MEASUREMENT
0%
PWM2
PWM
CONFIG
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
REMOTE 2 =
CPU TEMP
TACH1
PWM
CONFIG
PWM
MIN
100%
PWM1
CPU
FAN SINK
TACHOMETER 1
MEASUREMENT
0%
THERMAL CALIBRATION
LOCAL =
VRM TEMP
PWM
GENERATOR
PWM3
REAR
CHASSIS
TACH3
AN-613
MUX CONFIGURATION EXAMPLE
This is an example of how to configure the MUX in a
system using the ADT7460/ADT7463 to control three
fans. The CPU fan sink is controlled by PWM1, the front
chassis fan is controlled by PWM 2, and the rear chassis
fan is controlled by PWM3. The MUX is configured for
the following fan control behavior:
EXAMPLE MUX SETTINGS
<7:5> (BHVR) PWM1 CONFIGURATION REG 0x5C
101 = Fastest speed calculated by Local and Remote 2
Temp controls PWM1.
<7:5> (BHVR) PWM2 CONFIGURATION REG 0x5D
000 = Remote 1 Temp controls PWM2.
PWM1 (CPU fan sink) is controlled by the fastest speed
calculated by the Local (VRM Temp) and Remote 2 (processor) temperature. In this case, the CPU fan sink is
also being used to cool the VRM.
<7:5> (BHVR) PWM3 CONFIGURATION REG 0x5E
000 = Remote 1 Temp controls PWM3.
These settings configure the MUX, as shown in Figure 6.
PWM2 (front chassis fan) is controlled by the Remote 1
temperature (ambient).
PWM3 (rear chassis fan) is controlled by the Remote 1
temperature (ambient).
100%
REMOTE 2 =
CPU TEMP
TMIN
TRANGE
THERMAL CALIBRATION
LOCAL =
VRM TEMP
TMIN
TRANGE
0%
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
MUX
100%
TRANGE
PWM
GENERATOR
PWM2
FRONT
CHASSIS
TACH2
PWM
CONFIG
PWM
MIN
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 3
AND 4
MEASUREMENT
0%
CPU
FAN SINK
TACH1
TACHOMETER 2
MEASUREMENT
0%
PWM1
PWM
CONFIG
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
100%
TMIN
PWM
GENERATOR
PWM
MIN
THERMAL CALIBRATION
REMOTE 1 =
AMBIENT TEMP
PWM
CONFIG
PWM
MIN
THERMAL CALIBRATION
PWM
GENERATOR
PWM3
REAR
CHASSIS
TACH3
Figure 6. MUX Configuration Example
Rev. 1 | Page 6 of 27 | www.onsemi.com
–6–
REV. 0
AN-613
AN-613
Register 1 (Reg. 0x62), when set, keeps the fans
running
AN-613
Register 1 (Reg. 0x62), when set, keeps the fans running
STEP 3: DETERMINING T MIN SETTING FOR EACH
STEP
3: DETERMINING
T MIN
SETTING FOR EACH
THERMAL
CALIBRATION
CHANNEL
THERMAL
CALIBRATION
CHANNEL
TMIN is the temperature at which the fans will start to
STEP
DETERMINING
T at SETTING
FOR
EACH
TMIN on
is3: the
temperature
the
fans
willatstart
to
turn
under
automaticMIN
fanwhich
control.
The
speed
which
THERMAL
CALIBRATION
CHANNEL
turn
on
under
automatic
fan
control.
The
speed
at
which
the fan runs at TMIN is programmed later. The TMIN values
TMINfan
is the temperature
at which the
fans
start
to
the
at Ttemperature
later.
Thewill
TMIN
values
MIN is programmed
chosen runs
will be
channel
specific,
e.g.,
25°C
turn
on
under
automatic
fan
control.
The
speed
at
which
chosen
will be
temperature
channel
e.g., 25°C
for ambient
channel,
30°C for
VRM specific,
temperature,
and
the
fan
runs atchannel,
TMIN is programmed
later.
The TMIN values
for
ambient
30°C
for
VRM
temperature,
and
40°C for processor temperature.
chosen
be temperature
channel specific, e.g., 25°C
40°C forwill
processor
temperature.
TMINambient
is an 8-bit
twos complement
value
that can be profor
channel,
30°C for VRM
temperature,
and
TMIN is
8-bit
twos
complement
value
can register
be programmed
in 1°C
increments.
There
is that
a TMIN
40°C
foranprocessor
temperature.
grammed
1°C
increments.
There
is a TMIN channel:
register
associated in
with
each
temperature
measurement
TMIN is an 8-bit
twos
complement measurement
value that canchannel:
be proassociated
with
each
temperature
Remote 1, Local, and Remote 2 Temp. Once the TMIN
grammed
in
1°C increments.
There
is aOnce
TMIN the
register
Remote
1,
Local,
and
Remote
2
Temp.
TMIN
value is exceeded, the fan turns on and runs at minimum
associated
with each
temperature
measurement
channel:
value
is
exceeded,
the
fan
turns
on
and
runs
at
minimum
PWM duty cycle. The fan will turn off once temperature
Remote
1, cycle.
Local, The
andfan
Remote
2 Temp.
Once
the TMIN
PWM
duty
off once
temperature
has dropped
below TMIN
– will
THYSTturn
(detailed
later).
value
is exceeded,
fan
turns (detailed
on and runs
at minimum
has
dropped
belowthe
TMIN
–T
later).
HYST
To overcome
fanThe
inertia,
the turn
fan is
until two
PWM
duty cycle.
fan will
offspun
once up
temperature
To
overcome
fan
inertia,
fan isSee
spun
up
until
two
valid
tach rising
edges
counted.
the
Fan
Startup
has
dropped
below
TMINare
– Tthe
later).
HYST (detailed
valid
tach
rising
edges
are
counted.
See
the
Fan
Startup
Timeout section of the ADT7460/ADT7463 data sheet
To
overcome fan of
inertia,
the fan is spun updata
untilsheet
two
Timeout
the ADT7460/ADT7463
for more section
details. In some
cases, primarily for psychovalid
tach
rising
edges
are
counted.
See
the
Fan
Startup
for
more reasons,
details. Initsome
cases, primarily
acoustic
is desirable
that thefor
fanpsychonever
Timeout
section
ofitthe
ADT7460/ADT7463
data
sheet
acoustic
reasons,
is
desirable
that
the
never
switches off below TMIN. Bits <7:5> of enhancefan
acoustics
for
more
details.
In
some
cases,
primarily
for
psychoswitches off below TMIN. Bits <7:5> of enhance acoustics
acoustic reasons, it is desirable that the fan never
switches off below TMIN. Bits <7:5> of enhance acoustics
at PWM minimum duty cycle if the temperature should
at
minimum
duty cycle if the temperature should
fallPWM
below
TMIN.
Register
(Reg.
0x62), when set, keeps the fans running
fall
below1 T
.
MIN
at PWM minimum duty cycle if the temperature should
TMIN REGISTERS
fall
below TMIN.
T
MIN REGISTERS
Reg.
0x67 Remote 1 Temp TMIN = 0x5A (90°C default)
Reg.
1 Temp
= 0x5A
(90°C
default)
Reg. 0x67
0x68 Remote
Local Temp
TMIN T=MIN
0x5A
(90°C
default)
T
MIN REGISTERS
Reg.
0x68
Local
Temp
T
=
0x5A
(90°C
default)
MIN TMIN = 0x5A (90°C default)
Reg. 0x69 Remote 2 Temp
Reg. 0x69
0x67 Remote
Remote 2
1 Temp
Temp T
TMIN =
= 0x5A
0x5A (90°C
(90°C default)
default)
Reg.
MIN
Reg. 0x68 Local Temp TMIN = 0x5A (90°C default)
ENHANCE ACOUSTICS REG 1 (REG. 0x62)
Reg.
0x69 Remote
2 Temp T1MIN
= 0x5A
(90°C default)
ENHANCE
ACOUSTICS
0x62)
Bit 7 (MIN3)
= 0, PWM3REG
is OFF(REG.
(0% PWM
duty cycle)
Bit
7
(MIN3)
=
0,
PWM3
is
OFF
(0%
PWM
duty cycle)
when Temp is below TMIN – THYST.
ENHANCE
ACOUSTICS
REG– 1T (REG.
0x62)
when
Temp
is
below
T
.
HYST
Bit 7 (MIN3) = 1, PWM3MIN
runs at
PWM3 minimum duty
Bit 7
7 (MIN3)
(MIN3) =
= 1,
0, PWM3
PWM3 runs
is OFF
PWM
duty cycle)
Bit
at(0%
PWM3
minimum
duty
cycle
below TMIN
– THYST.
when below
Temp T
is below
TMIN
– THYST.
cycle
–
T
.
MIN
HYST
Bit 6
OFF
PWM
duty cycle)
7 (MIN2)
(MIN3) = 0,
1, PWM2
PWM3 is
runs
at(0%
PWM3
minimum
duty
Bit
6 (MIN2)
= 0,
PWM2
(0%
when
Temp T
is
below
TMIN
THYST
. PWM duty cycle)
cycle
below
– THYST
.is –OFF
MIN
when
Temp is
below
TMIN
– Tat
.
HYST
Bit 6 (MIN2)
= 1,
PWM2
runs
PWM2
minimum duty
Bit
6
(MIN2)
=
0,
PWM2
is
OFF
(0%
PWM
duty cycle)
Bit
6
(MIN2)
=
1,
PWM2
runs
at
PWM2
minimum
duty
cycle below TMIN – THYST.
when
Temp
is
below
T
–
T
.
MIN
HYST
cycle below TMIN – THYST
.
Bit 5
OFF
PWM
duty cycle)
6 (MIN1)
(MIN2) = 0,
1, PWM1
PWM2 is
runs
at(0%
PWM2
minimum
duty
Bit
5 (MIN1)
= 0,
PWM1
is –OFF
(0%
PWM duty cycle)
when
Temp T
is
below
T
T
.
cycle
below
–
T
.
MIN
HYST
MIN
HYST
when
Temp is
below
TMIN
– Tat
.
HYST
Bit 5 (MIN1)
= 1,
PWM1
runs
PWM1
minimum duty
Bit
5
(MIN1)
=
0,
PWM1
is
OFF
(0%
PWM
duty cycle)
Bit
5
(MIN1)
=
1,
PWM1
runs
at
PWM1
minimum
duty
cycle below TMIN – THYST.
when
Temp T
is below
TMIN
– THYST.
cycle below
–
T
.
MIN
HYST
Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty
cycle below TMIN – THYST.
100%
PWM DUTY
PWM
PWM
CYCLE
DUTY
DUTY
CYCLE
CYCLE
100%
100%
0%
0%
TMIN
TMIN
0%
TMIN
PWM
MIN
PWM
MIN
THERMAL CALIBRATION
THERMAL CALIBRATION
100%
100%
�
PWM
MIN
THERMAL CALIBRATION
�
100%
REMOTE 2 =
CPU TEMP
REMOTE
2=
CPU TEMP
REMOTE 2 =
CPU TEMP
TMIN
TRANGE
TMIN
TRANGE
0%
THERMAL CALIBRATION
TMIN
TRANGE
100%
0%
100%
100%
TMIN
TRANGE
VRM TEMP
TMIN
TRANGE
LOCAL =
VRM TEMP
THERMAL CALIBRATION
TMIN
TRANGE
0%
0%
THERMAL CALIBRATION
100%
0%
100%
THERMAL CALIBRATION
100%
REMOTE 1 =
AMBIENT
TEMP
REMOTE
1=
AMBIENT TEMP
REMOTE 1 =
AMBIENT TEMP
PWM
MIN
PWM
MIN
THERMAL CALIBRATION
THERMAL CALIBRATION
LOCAL =
VRM
TEMP
LOCAL
=
�
0%
TMIN
TRANGE
TMIN
TRANGE
TMIN
TRANGE
MUX
MUX
�
PWM
MIN
MUX
�
�
PWM
MIN
PWM
MIN
�
PWM
MIN
�
0%
�
0%
RAMP
CONTROL
RAMP
(ACOUSTIC
CONTROL
ENHANCEMENT
(ACOUSTIC
ENHANCEMENT
RAMP
TACHOMETER
CONTROL 1
MEASUREMENT
(ACOUSTIC
TACHOMETER
ENHANCEMENT1
MEASUREMENT
TACHOMETER 1
MEASUREMENT
RAMP
CONTROL
RAMP
(ACOUSTIC
CONTROL
ENHANCEMENT
(ACOUSTIC
ENHANCEMENT
RAMP
TACHOMETER
CONTROL 2
MEASUREMENT
(ACOUSTIC
TACHOMETER
ENHANCEMENT2
MEASUREMENT
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
RAMP
(ACOUSTIC
CONTROL
ENHANCEMENT
(ACOUSTIC
ENHANCEMENT
RAMP
TACHOMETER
3
CONTROL
AND 4
(ACOUSTIC
TACHOMETER
3
MEASUREMENT
ENHANCEMENT
AND 4
MEASUREMENT
PWM
CONFIG
PWM
CONFIG
PWM
GENERATOR
PWM
PWM
CONFIG
GENERATOR
PWM1
PWM
GENERATOR
TACH1
PWM1
TACH1
PWM
CONFIG
PWM
CONFIG
PWM
GENERATOR
PWM
PWM
CONFIG
GENERATOR
PWM
GENERATOR
PWM
CONFIG
PWM
CONFIG
PWM
GENERATOR
PWM
PWM
CONFIG
GENERATOR
CPU
FAN
CPU SINK
FAN SINK
CPU
FAN SINK
TACH1
PWM2
PWM2
TACH2
PWM2
TACH2
FRONT
CHASSIS
FRONT
CHASSIS
FRONT
CHASSIS
TACH2
PWM3
PWM3
REAR
CHASSIS
REAR
CHASSIS
PWM
GENERATOR
TACHOMETER 3
AND 4
MEASUREMENT
0%
PWM1
REV. 0
REV. 0
Figure 7. Understanding the TMIN Parameter
Figure 7. Understanding the TMIN Parameter
–7–
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| www.onsemi.com
–7–
Figure 7. Understanding the TMIN Parameter
REV. 0
–7–
TACH3
PWM3
TACH3
TACH3
REAR
CHASSIS
AN-613
STEP 4: DETERMINING PWM MIN FOR EACH PWM (FAN)
OUTPUT
PWMMIN is the minimum PWM duty cycle at which each
fan in the system will run. It is also the “start” speed for
each fan under automatic fan control once the temperature rises above TMIN. For maximum system acoustic
benefit, PWMMIN should be as low as possible. Starting
the fans at higher speeds than necessary will merely
make the system louder than necessary. Depending on
the fan used, the PWMMIN setting should be in the 20% to
33% duty cycle range. This value can be found through
fan validation.
PWM DUTY CYCLE
100%
M1
PW
PWM2MIN
PWM1MIN
0%
TMIN
TEMPERATURE
Figure 9. Operating Two Different Fans from a Single
Temperature Channel
100%
PWM DUTY CYCLE
M2
PW
PROGRAMMING THE PWM MIN REGISTERS
The PWMMIN registers are 8-bit registers that allow the
minimum PWM duty cycle for each output to be configured anywhere from 0% to 100%. This allows minimum
PWM duty cycle to be set in steps of 0.39%.
PWMMIN
The value to be programmed into the PWMMIN register is
given by:
0%
TMIN
Value (decimal) = PWMMIN/0.39
TEMPERATURE
Example 1: For a minimum PWM duty cycle of 50%,
Figure 8. PWMMIN Determines Minimum PWM
Duty Cycle
Value (decimal) = 50/0.39 = 128 decimal
Value = 128 decimal or 80 hex
It is important to note that more than one PWM
output can be controlled from a single temperature
measurement channel. For example, Remote 1 Temp
can control PWM1 and PWM2 outputs. If two different
fans are used on PWM and PWM2, then the fan characteristics can be set up differently. As a result, Fan 1
driven by PWM1 can have a different PWMMIN value than
that of Fan 2 connected to PWM2. Figure 9 illustrates
this as PWM1MIN (front fan) is turned on at a minimum
duty cycle of 20%, whereas PWM2MIN (rear fan) turns
on at a minimum of 40% duty cycle. Note, however,
that both fans turn on at exactly the same temperature, defined by TMIN.
Example 2: For a minimum PWM duty cycle of 33%,
Value (decimal) = 33/0.39 = 85 decimal
Value = 85 decimal or 54 hex
PWM MIN REGISTERS
Reg. 0x64 PWM1 Min Duty Cycle = 0x80 (50% default)
Reg. 0x65 PWM2 Min Duty Cycle = 0x80 (50% default)
Reg. 0x66 PWM3 Min Duty Cycle = 0x80 (50% default)
FAN SPEED AND PWM DUTY CYCLE
It should be noted that PWM duty cycle does not
directly correlate to fan speed in RPM. Running a fan at
33% PWM duty cycle does not equate to running the fan
at 33% speed. Driving a fan at 33% PWM duty cycle
actually runs the fan at closer to 50% of its full speed.
This is because fan speed in %RPM relates to the square
root of PWM duty cycle. Given a PWM square wave as
the drive signal, fan speed in RPM equates to:
% fan speed = PWM duty cycle × 10
Rev. 1 | Page 8 of 27 | www.onsemi.com
–8–
REV. 0
AN-613
TRANGE is implemented as a slope, which means as
PWMMIN is changed, TRANGE changes but the actual slope
remains the same. The higher the PWMMIN value, the
smaller the effective TRANGE will be, i.e., the fan will reach
full speed (100%) at a lower temperature.
STEP 5: DETERMINING TRANGE FOR EACH TEMPERATURE
CHANNEL
TRANGE is the range of temperature over which automatic
fan control occurs once the programmed TMIN temperature has been exceeded. TRANGE is actually a temperature
slope and not an arbitrary value, i.e., a TRANGE of 40°C
only holds true for PWMMIN = 33%. If PWMMIN is increased or decreased, the effective TRANGE is changed, as
described later.
PWM DUTY CYCLE
100%
TRANGE
PWM DUTY CYCLE
100%
50%
33%
25%
10%
0%
30�C
40�C
45�C
54�C
PWMMIN
0%
TMIN
TMIN
TEMPERATURE
Figure 12. Increasing PWMMIN Changes Effective
TRANGE
Figure 10. TRANGE Parameter Affects Cooling Slope
The TRANGE or fan control slope is determined by the following procedure:
For a given TRANGE value, the temperature at which the
fan will run at full speed for different PWMMIN values can
easily be calculated:
1. Determine the maximum operating temperature for
that channel, e.g., 70°C.
2. Determine experimentally the fan speed (PWM duty
cycle value) that will not exceed the temperature at
the worst-case operating points, e.g., 70°C is reached
when the fans are running at 50% PWM duty cycle.
3. Determine the slope of the required control loop to
meet these requirements.
4. Use best fit approximation to determine the most
suitable TRANGE value. ADT7460/ADT7463 evaluation
software is available to calculate the best fit value.
Ask your local Analog Devices representative for
more details.
TMAX = TMIN + ((Max D. C. – Min D. C.) � TRANGE /170
where
TMAX = Temperature at which the fan runs full speed
TMIN = Temperature at which the fan will turn on
Max D. C. = Maximum duty cycle (100%) = 255 decimal
Min D. C. = PWMMIN
TRANGE = PWM duty cycle versus temperature slope
Example: Calculate TMAX, given TMIN = 30°C, TRANGE =
40°C, and PWMMIN = 10% duty cycle = 26 decimal
TMAX = TMIN + (Max D. C. – Min D. C.) � TRANGE /170
TMAX = 30°C + (100% – 10%) � 40°C/170
TMAX = 30°C + (255 – 26) � 40°C/170
TMAX = 84°C (effective TRANGE = 54°C)
PWM DUTY CYCLE
100%
Example: Calculate TMAX, given TMIN = 30°C, TRANGE =
40°C, and PWMMIN = 25% duty cycle = 64 decimal
TMAX = TMIN + (Max D. C. – Min D. C.) � TRANGE /170
TMAX = 30°C + (100% – 25%) � 40°C/170
TMAX = 30°C + (255 – 64) � 40°C/170
TMAX = 75°C (effective TRANGE = 45°C)
50%
33%
0%
Example: Calculate TMAX, given TMIN = 30°C, TRANGE =
40°C, and PWMMIN = 33% duty cycle = 85 decimal
30�C
40�C
TMAX = TMIN + (Max D. C. – Min D. C.) � TRANGE /170
TMAX = 30°C + (100% – 33%) � 40°C/170
TMAX = 30°C + (255 – 85) � 40°C/170
TMAX = 70°C (effective TRANGE = 40°C)
TMIN
Figure 11. Adjusting PWMMIN Affects TRANGE
Rev. 1 | Page 9 of 27 | www.onsemi.com
REV. 0
–9–
AN-613
Example: Calculate TMAX, given TMIN = 30°C, TRANGE =
40°C, and PWMMIN = 50% duty cycle = 128 decimal
Remember that %PWM duty cycle does not correspond
to %RPM. %RPM relates to the square root of the PWM
duty cycle.
TMAX = TMIN + (Max D. C. – Min D. C.) � TRANGE /170
TMAX = 30°C + (100% – 50%) � 40°C/170
TMAX = 30°C + (255 – 128) � 40°C/170
TMAX = 60°C (effective TRANGE = 30°C)
% fan speed = PWM duty cycle × 10
100
90
SELECTING A T RANGE SLOPE
The TRANGE value can be selected for each temperature
channel: Remote 1, Local, and Remote 2 Temp. Bits
<7:4> (TRANGE) of registers 0x5F to 0x61 define the TRANGE
value for each temperature channel.
PWM DUTY CYCLE – %
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
2°C
2.5°C
3.33°C
4°C
5°C
6.67°C
8°C
10°C
13.33°C
16°C
20°C
26.67°C
32°C (default)
40°C
53.33°C
80°C
4 C
5 C
70
6.67 C
60
8 C
10 C
50
13.3 C
16 C
40
20 C
30
26.6 C
32 C
20
40 C
10
53.3 C
0
0
20
40
60
80
TEMPERATURE ABOVE TMIN
100
80 C
120
100
2C
2.5 C
90
3.33 C
80
FAN SPEED – % OF MAX
TRANGE
3.33 C
80
Table I. Selecting a TRANGE Value
Bits <7:4>*
2C
2.5 C
4 C
5 C
70
6.67 C
8 C
60
10 C
50
13.3 C
16 C
40
20 C
30
26.6 C
32 C
20
40 C
10
* Register 0x5F configures Remote 1 T RANGE
Register 0x60 configures Local T RANGE
Register 0x61 configures Remote 2 T RANGE
0
SUMMARY OF T RANGE FUNCTION
When using the automatic fan control function, the temperature at which the fan reaches full speed can be
calculated by
TMAX = TMIN + TRANGE
20
40
60
80
TEMPERATURE ABOVE TMIN
100
80 C
120
Figure 13. TRANGE vs. Actual Fan Speed Profile
Figure 13 shows PWM duty cycle versus temperature for
each TRANGE setting. The lower graph shows how each
TRANGE setting affects fan speed versus temperature. As
can be seen from the graph, the effect on fan speed is
nonlinear. The graphs in Figure 13 assume that the fan
starts from 0% PWM duty cycle. Clearly, the minimum
PWM duty cycle, PWMMIN, needs to be factored in to see
how the loop actually performs in the system. Figure 14
shows how TRANGE is affected when the PWMMIN value is
set to 20%. It can be seen that the fan will actually run at
about 45% fan speed when the temperature exceeds TMIN.
(1)
Equation 1 only holds true when PWMMIN = 33% PWM
duty cycle.
Increasing or decreasing PWMMIN will change the effective TRANGE, although the fan control will still follow the
same PWM duty cycle to temperature slope. The effective TRANGE for different PWMMIN values can be
calculated using Equation 2.
TMAX = TMIN + (Max D. C. – Min D. C.) � TRANGE /170
53.3 C
0
(2)
where:
(Max D. C. – Min D. C.) � TRANGE /170 = effective TRANGE
value.
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2.5 C
90
3.33 C
4 C
5 C
70
6.67 C
8 C
60
10 C
50
13.3 C
20 C
30
26.6 C
32 C
20
53.3 C
0
20
40
60
80
TEMPERATURE ABOVE TMIN
100
120
100
80 C
90
100
80
2C
2.5 C
90
3.33 C
80
FAN SPEED – % OF MAX
The CPU fan is configured to run at PWMMIN = 10%.
40 C
10
4 C
5 C
70
6.67 C
60
8 C
10 C
50
70
60
50
40
30
13.3 C
40
20
16 C
10
20 C
30
26.6 C
0
32 C
20
0
10
20
30
40
50
60
70
80
90
100
80
90
100
TEMPERATURE ABOVE TMIN
40 C
10
0
The front chassis fan is configured to run at
PWMMIN = 20%. The rear chassis fan is configured to run
at PWMMIN = 30%.
16 C
40
PWM DUTY CYCLE – %
PWM DUTY CYCLE – %
80
0
This example uses the MUX configuration described
in Step 2, with the ADT7460/ADT7463 connected as
shown in Figure 6. Both CPU temperature and VRM temperature drive the CPU fan connected to PWM1.
Ambient temperature drives the front chassis fan and
rear chassis fan connected to PWM2 and PWM3.
2C
100
53.3 C
0
20
40
60
80
TEMPERATURE ABOVE TMIN
100
120
100
80 C
90
80
FAN SPEED – % MAX RPM
Figure 14. TRANGE, % Fan Speed Slopes with
PWMMIN = 20%
EXAMPLE: DETERMINING T RANGE FOR EACH
TEMPERATURE CHANNEL
The following example is used to show how TMIN, TRANGE
settings might be applied to three different thermal
zones. In this example, the following TRANGE values
apply:
70
60
50
40
30
20
10
TRANGE = 80°C for Ambient Temperature
TRANGE = 53.3°C for CPU Temperature
TRANGE = 40°C for VRM Temperature
0
0
20
30
40
50
60
70
TEMPERATURE ABOVE TMIN
Figure 15. TRANGE, % Fan Speed Slopes for VRM,
Ambient, and CPU Temperature Channels
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STEP 6: DETERMINING T THERM FOR EACH TEMPERATURE
CHANNEL
STEP 6: DETERMINING T THERM FOR EACH TEMPERATURE
TTHERM is the absolute maximum
temperature allowed
CHANNEL
on a temperature channel. Above this temperature, a
TTHERM is the absolute maximum temperature allowed
component
such as the CPU or VRM may be operating
on a temperature channel. Above this temperature, a
beyond its safe operating limit. When the temperature
component such as the CPU or VRM may be operating
measured exceeds TTHERM, all fans are driven at 100% PWM
beyond its safe operating limit. When the temperature
duty cycle (full speed) to provide critical system cooling.
measured exceeds TTHERM, all fans are driven at 100% PWM
The fans remain running
100% until the temperature drops
duty cycle (full speed) to provide critical system cooling.
below TTHERM – hysteresis. The hysteresis value is the
The fans remain running 100% until the temperature drops
number programmed into hysteresis registers 0x6D and
below TTHERM – hysteresis. The hysteresis value is the
0x6E. The default
hysteresis value is 4°C.
number programmed into hysteresis registers 0x6D and
The0x6E.
TTHERM
should
be considered
Thelimit
default
hysteresis
value is 4°C.the maximum
worst-case operating temperature of the system. Since
The TTHERM limit should be considered the maximum
exceeding
any TTHERM limit runs all fans at 100%, it has
worst-case operating temperature of the system. Since
very negative acoustic effects. Ultimately, this limit
exceeding any T
limit runs all fans at 100%, it has
should be set up asTHERM
a failsafe, and one should ensure
very negative acoustic effects. Ultimately, this limit
that it is not exceeded under normal system operating
should be set up as a failsafe, and one should ensure
conditions.
that it is not exceeded under normal system operating
conditions.
Note that the TTHERM limits are nonmaskable and affect
the fan speed no matter what automatic fan control setNote that the TTHERM limits are nonmaskable and affect
tings are configured.
This allows some flexibility since a
the fan speed no matter what automatic fan control setTRANGE value can be selected based on its slope, while a
tings are configured. This allows some flexibility since a
“hard limit,” e.g., 70°C, can be programmed as TMAX (the
TRANGE value can be selected based on its slope, while a
temperature
at which the fan reaches full speed) by set“hard limit,” e.g., 70°C, can be programmed as TMAX (the
ting TTHERM to 70°C.
temperature at which the fan reaches full speed) by setting TTHERM to 70°C.
THERM REGISTERS
Reg. 0x6A Remote 1 THERM limit = 0x64 (100°C default)
THERM REGISTERS
Reg. 0x6B Local Temp THERM limit = 0x64 (100°C
Reg. 0x6A Remote 1 THERM limit = 0x64 (100°C default)
default)
Reg. 0x6B Local Temp THERM limit = 0x64 (100°C
Reg. 0x6C Remote 2 THERM limit = 0x64 (100°C default)
default)
Reg. 0x6C Remote 2 THERM limit = 0x64 (100°C default)
HYSTERESIS REGISTERS
Reg. 0x6D Remote 1, Local Hysteresis Register
HYSTERESIS REGISTERS
<7:4> = Remote 1 Temp Hysteresis (4°C default)
Reg. 0x6D Remote 1, Local Hysteresis Register
<3:0> = Local Temp Hysteresis (4°C default)
<7:4> = Remote 1 Temp Hysteresis (4°C default)
Reg.
0x6E= Remote
2 Temp
Hysteresis
Register
<3:0>
Local Temp
Hysteresis
(4°C
default)
<7:4> = Remote 2 Temp Hysteresis (4°C default)
Reg. 0x6E Remote 2 Temp Hysteresis Register
Since
each
hysteresis
settingHysteresis
is four bits,(4°C
hysteresis
<7:4>
= Remote
2 Temp
default)values
are programmable from 1°C to 15°C. It is not recomSince each hysteresis setting is four bits, hysteresis values
mended that hysteresis values ever be programmed to
are programmable from 1°C to 15°C. It is not recom0°C, as this actually disables hysteresis. In effect, this
mended that hysteresis values ever be programmed to
would cause the fans to cycle between normal speed and
0°C, as this actually disables hysteresis. In effect, this
100% speed, creating unsettling acoustic noise.
would cause the fans to cycle between normal speed and
100% speed, creating unsettling acoustic noise.
TRANGE
TRANGE
100%
PWM DUTY CYCLE
PWM DUTY CYCLE
100%
0%
0%
TTHERM
TMIN
TTHERM
TMIN
THERMAL CALIBRATION
PWM
PWMRAMP CONTROL
PWM
CONFIG
MIN (ACOUSTIC
GENERATOR
ENHANCEMENT)
RAMP CONTROL
PWM
(ACOUSTIC
GENERATOR
ENHANCEMENT)
TACHOMETER
1
MEASUREMENT
THERMAL CALIBRATION
100%
REMOTE 2 =
CPU TEMP
TMIN
REMOTE 2 =
CPU TEMP
TRANGE
0%
0%
THERMAL
CALIBRATION
T
T
MIN
100%
TMIN
LOCAL =
VRM TEMP
TRANGE
THERMAL CALIBRATION
TMIN
TRANGE
0%
100%
THERMAL CALIBRATION
100%
REMOTE 1 =
AMBIENT TEMP
TMIN
REMOTE 1 =
AMBIENT TEMP
TMIN
TRANGE
0%
TRANGE
MUX
MUX
0%
0%
PWM
CONFIG
PWM
PWM
RAMP CONTROL
CONFIG
PWM
MIN (ACOUSTIC
GENERATOR
ENHANCEMENT)
RAMP CONTROL
PWM
(ACOUSTIC
GENERATOR
ENHANCEMENT)
TACHOMETER
2
MEASUREMENT
THERMAL CALIBRATION
LOCAL =
VRM TEMP
TACHOMETER 1
MEASUREMENT
PWM
MIN
RANGE
100%
PWM
CONFIG
PWM
MIN
100%
PWM
MIN
TACHOMETER 2
MEASUREMENT
PWMRAMP CONTROL
MIN (ACOUSTIC
ENHANCEMENT)
RAMP CONTROL
(ACOUSTIC
TACHOMETER
3
ENHANCEMENT)
AND 4
MEASUREMENT
TACHOMETER 3
AND 4
MEASUREMENT
PWM
CONFIG
PWM
PWM
CONFIG
GENERATOR
PWM
GENERATOR
PWM1
PWM1
TACH1
CPU
FAN SINK
CPU
FAN SINK
TACH1
PWM2
PWM2
TACH2
FRONT
CHASSIS
FRONT
CHASSIS
TACH2
PWM3
PWM3
TACH3
TACH3
REAR
CHASSIS
REAR
CHASSIS
Figure 16. Understanding How TTHERM Relates to Automatic Fan Control
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Figure 16. Understanding
TTHERM
Relates to Automatic Fan Control
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Note that the THYST setting applies not only to the
temperature hysteresis for fan turn on/off, but the same
setting is used for the TTHERM hysteresis value described
in Step 6. So programming registers 0x6D and 0x6E sets
the hysteresis for both fan on/off and the THERM function.
STEP 7: DETERMINING T HYST FOR EACH TEMPERATURE
CHANNEL
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 temperature is hovering at about the TMIN setting.
HYSTERESIS REGISTERS
Reg. 0x6D Remote 1, Local Hysteresis Register
<7:4> = Remote 1 Temp Hysteresis (4°C default)
<3:0> = Local Temp Hysteresis (4°C default)
The THYST value chosen will determine 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 1°C to 15°C. Larger values of
THYST prevent the fans from chattering on and off as previously described. The THYST default value is set at 4°C.
Reg. 0x6E Remote 2 Temp Hysteresis Register
<7:4> = Remote 2 Temp Hysteresis (4°C default)
Note that in some applications, it is required that the
fans not turn off below TMIN but remain running at
PWMMIN. Bits <7:5> of Enhance Acoustics Register 1
(Reg. 0x62) 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.
TRANGE
PWM DUTY CYCLE
100%
THYST
0%
TMIN
TTHERM
PWM
MIN
THERMAL CALIBRATION
100%
�
REMOTE 2 =
CPU TEMP
TMIN
TRANGE
0%
PWM
MIN
100%
MUX
TMIN
TRANGE
�
0%
100%
TRANGE
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
CPU
FAN SINK
TACH1
PWM
GENERATOR
PWM2
TACH2
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM3
TACH3
Figure 17. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis
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FRONT
CHASSIS
PWM
CONFIG
TACHOMETER 3
AND 4
MEASUREMENT
0%
PWM1
PWM
CONFIG
PWM
MIN
�
TMIN
PWM
GENERATOR
TACHOMETER 2
MEASUREMENT
THERMAL CALIBRATION
REMOTE 1 =
AMBIENT TEMP
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
THERMAL CALIBRATION
LOCAL =
VRM TEMP
PWM
CONFIG
REAR
CHASSIS
AN-613
3. Worst-Case Chassis Airflow. The same motherboard
can be used in a number of different chassis configurations. The design of the chassis and 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, e.g., placing a
computer against a wall can block the air ducts and
reduce system airflow.
ENHANCE ACOUSTICS REG 1 (REG. 0x62)
Bit 7 (MIN3) = 0, PWM3 is OFF (0% PWM duty cycle)
when Temp is below TMIN – THYST.
Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty
cycle below TMIN – THYST.
Bit 6 (MIN2) = 0, PWM2 is OFF (0% PWM duty cycle)
when Temp is below TMIN – THYST.
Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty
cycle below TMIN – THYST.
Bit 5 (MIN1) = 0, PWM1 is OFF (0% PWM duty cycle)
when Temp is below TMIN – THYST.
Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty
cycle below TMIN – THYST.
VENTS
FAN
FAN
I/O CARDS
DYNAMIC T MIN CONTROL MODE
In addition to the automatic fan speed control mode described in the previous section, the ADT7460/ADT7463
have a mode that extends the basic automatic fan speed
control loop. Dynamic TMIN control allows the
ADT7460/ADT7463 to intelligently adapt the system’s
cooling solution for best system performance or lowest
possible system acoustics, depending on user or design
requirements.
POWER
SUPPLY
I/O CARDS
GOOD CPU AIRFLOW
VENTS
CPU
POWER
SUPPLY
CPU
POOR CPU
AIRFLOW
DRIVE
BAYS
FAN
DRIVE
BAYS
VENTS
GOOD VENTING = GOOD AIR EXCHANGE
POOR VENTING = POOR AIR EXCHANGE
Figure 18. Chassis Airflow Issues
AIM OF THIS SECTION
This section has two primary goals:
4. Worst-Case Processor Power Consumption. This is a
data sheet maximum that does not necessarily reflect
the true processor power consumption. Designing for
worst-case CPU power consumption results in that
the processor getting overcooled (generating excess
system noise).
1. To show how dynamic TMIN control alleviates the
need for designing for worst-case conditions.
2. To illustrate how the dynamic TMIN control function
significantly reduces system design and validation
time.
5. Worst-Case Peripheral Power Consumptions. The
tendency is to design to data sheet maximums for
these components (again overcooling the system).
DESIGNING FOR WORST-CASE CONDITIONS
When designing a system, you always design for worstcase conditions. In PC design, the worst-case conditions
include, but are not limited to:
6. Worst-Case Assembly. Every system manufactured is
unique because of manufacturing variations. Heat
sinks may be loose fitting or slightly misaligned. Too
much or too little thermal grease may be used, or variations in application pressure for thermal interface
material can affect the efficiency of the thermal solution.
How can this be accounted for in every system? Again,
the system is designed for the worst case.
1. Worst-Case Altitude. A computer can be operated at
different altitudes. The altitude affects the relative air
density, which will alter 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 the fan can spin 40% slower, and make less
noise, at sea level than at 10,000 ft while keeping the
system at the same temperature at both locations.
TA
�SA
HEAT
SINK
�TIMS
THERMAL
INTERFACE
MATERIAL
2. Worst-Case Fan. Due to manufacturing tolerances,
fan speeds in RPM are 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 will
negatively impact system acoustics since they run
faster and generate more noise.
�CTIM
INTEGRATED
HEAT
SPREADER
TS
�CA
TTIM
TC
�CS
�JA
�TIMC
PROCESSOR
SUBSTRATE
EPOXY
THERMAL INTERFACE MATERIAL
TTIM
�JTIM
TJ
Figure 19. Thermal Model
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solution to maintain each zone temperature as closely
as possible to their target operating points.
The design usually accounts for worst-case conditions
in all of these cases.
Note, however, that the actual system is almost never
operated at worst-case conditions.
OPERATING POINT REGISTERS
Reg. 0x33 Remote 1 Operating Point = 0x64 (100°C)
Reg. 0x34 Local Temp Operating Point = 0x64 (100°C)
Reg. 0x35 Remote 2 Operating Point = 0x64 (100°C)
The alternative to designing for the worst case is to use
the dynamic TMIN control function.
PWM DUTY CYCLE
DYNAMIC T MIN CONTROL—OVERVIEW
Dynamic TMIN Control mode builds upon the basic automatic fan control loop by adjusting the TMIN
value based on system performance and measured temperature. Why is this important?
Instead of designing for the worst case, the system
thermals can be defined as “operating zones.” The
ADT7460/ADT7463 will self-adjust its fan control loop to
maintain an operating zone temperature or system target temperature. For example, you can specify that the
ambient temperature in a system should be maintained
at 50°C. If the temperature is below 50°C, the fans may not
need to run or may run very slowly. If the temperature is
higher than 50°C, the fans need to throttle up. How is this
different from the automatic fan control mode?
TEMPERATURE
TLOW
Figure 20. Dynamic TMIN Control Loop
Figure 20 shows an overview of the parameters that
affect the operation of the dynamic TMIN control loop. A
brief description of each parameter follows:
1. TLOW. If temperature drops below the TLOW limit, an
error flag is set in a status register and an SMBALERT
interrupt can be generated.
2. THIGH. If temperature exceeds the THIGH limit, an error
flag gets set in a status register and an SMBALERT
interrupt can be generated.
3. TMIN. This is the temperature at which the fan turns on
under automatic fan speed control.
4. Operating Point. This temperature defines the target
temperature or optimal operating point for a
particular temperature zone. The ADT7460/ADT7463
attempt to maintain system temperature at about the
operating point by adjusting the TMIN parameter of
the control loop.
5. TTHERM. If temperature exceeds this critical limit, the
fans can be run at 100% for maximum cooling.
6. TRANGE. This programs the PWM duty cycle versus
temperature control slope.
The challenge presented by any thermal design is finding the right settings to suit the system’s fan control
solution. This can involve designing for the worst case
(as previously outlined), followed by weeks of system
thermal characterization, and finally fan acoustic optimization (for psycho-acoustic reasons). Getting the most
benefit from the automatic fan control mode involves
characterizing the system to find the best TMIN and
TRANGE settings for the control loop, and the best
PWMMIN value for the quietest fan speed setting. Using
the ADT7460/ADT7463’s dynamic TMIN control mode
shortens the characterization time and alleviates tweaking the control loop settings because the device can
self-adjust during system operation.
DYNAMIC T MIN CONTROL—THE SPECIFICS
The dynamic TMIN control mode is operated by specifying the “operating zone temperatures” required for the
system. Associated with this control mode are three
operating point registers, one for each temperature
channel. This allows the system thermal solution to be
broken down into distinct thermal zones, e.g., CPU operating temperature = 70°C, VRM operating temperature =
80°C, ambient operating temperature = 50°C. The
ADT7460/ADT7463 will dynamically alter the control
DYNAMIC T MIN CONTROL PROGRAMMING
Since the dynamic TMIN control mode is a basic extension
of the automatic fan control mode, the automatic fan control mode parameters should be programmed first. Follow
the seven steps in the Automatic Fan Control section of the
ADT7460/ADT7463 data sheet before proceeding with
dynamic TMIN control mode programming.
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TMIN OPERATING THIGH TTHERM TRANGE
POINT
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the temperature zone to get closer to the operating
point. Likewise, too high a TMIN value will cause the
operating point to be exceeded, and in turn, the
ADT7460/ADT7463 will reduce TMIN to turn the fans on
earlier to cool the system.
STEP 8: DETERMINING THE OPERATING POINT FOR
EACH TEMPERATURE CHANNEL
The operating point for each temperature channel is the
optimal temperature for that thermal zone. The hotter
each zone is allowed to be, the quieter the system since
the fans are not required to run at 100% all of the time.
The ADT7460/ADT7463 will increase/decrease fan
speeds as necessary to maintain operating point temperature. This allows for system-to-system variation
and removes the need for worst-case design. As long as
a sensible operating point value is chosen, any TMIN
value can be selected in the system characterization. If
the TMIN value is too low, the fans will run sooner than
required, and the temperature will be below the operating point. In response, the ADT7460/ADT7463 will
increase TMIN to keep the fans off for longer and allow
PROGRAMMING OPERATING POINT REGISTERS
There are three operating point registers, one associated with each temperature channel. These 8-bit
registers allow the operating point temperatures to be
programmed with 1°C resolution.
OPERATING POINT REGISTERS
Reg. 0x33 Remote 1 Operating Point = 0x64 (100°C)
Reg. 0x34 Local Temp Operating Point = 0x64 (100°C)
Reg. 0x35 Remote 2 Operating Point = 0x64 (100°C)
PWM
CONFIG
OPERATING PWM
POINT
MIN
THERMAL CALIBRATION
100%
REMOTE 2 =
CPU TEMP
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
0%
TMIN
TACHOMETER 1
MEASUREMENT
TRANGE
100%
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
MUX
TMIN
TRANGE
THERMAL CALIBRATION
100%
TMIN
TRANGE
PWM
GENERATOR
TACHOMETER 3
AND 4
MEASUREMENT
0%
PWM2
FRONT
CHASSIS
TACH2
PWM
CONFIG
PWM
MIN
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
REMOTE 1 =
AMBIENT TEMP
CPU
FAN SINK
TACH1
TACHOMETER 2
MEASUREMENT
0%
PWM1
PWM
CONFIG
PWM
MIN
THERMAL CALIBRATION
LOCAL =
VRM TEMP
PWM
GENERATOR
PWM
GENERATOR
PWM3
TACH3
REAR
CHASSIS
Figure 21. Operating Point Value Dynamically Adjusts Automatic Fan Control Settings
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STEP 9: DETERMINING THE HIGH AND LOW LIMITS FOR
EACH TEMPERATURE CHANNEL
The low limit defines the temperature at which the TMIN
value will start to be increased if temperature falls
below this value. This has the net effect of reducing the
fan speed, allowing the system to get hotter. An interrupt can be generated when the temperature drops
below the low limit.
PROGRAMMING HIGH AND LOW LIMITS
There are six limit registers; a high limit and low limit
are associated with each temperature channel. These
8-bit registers allow the high and low limit temperatures
to be programmed with 1°C resolution.
TEMPERATURE LIMIT REGISTERS
Reg. 0x4E Remote 1 Temp Low Limit = 0x81
Reg. 0x4F Remote 1 Temp High Limit = 0x7F
Reg. 0x50 Local Temp Low Limit = 0x81
Reg. 0x51 Local Temp High Limit = 0x7F
Reg. 0x52 Remote 2 Temp Low Limit = 0x81
Reg. 0x53 Remote 2 Temp High Limit = 0x7F
The high limit defines the temperature at which the TMIN
value will start to be reduced if temperature increases
above this value. This has the net effect of increasing fan
speed in order to cool down the system. An interrupt
can be generated when the temperature rises above the
high limit.
Figure 22. Dynamic TMIN Control in Operation
Rev. 1 | Page 17 of 27 | www.onsemi.com
REV. 0
–17–
AN-613
Table II. Cycle Bit Assignments
HOW DOES DYNAMIC T MIN CONTROL WORK?
The basic premise is as follows:
1. Set the target temperature for the temperature zone,
which could be, for example, the Remote 1 thermal
diode. This value is programmed to the Remote 1
operating temperature register.
2. As the temperature in that zone (Remote 1 temperature)
rises toward and exceeds the operating point temperature, TMIN is reduced and the fan speed increases.
3. As the temperature drops below the operating point
temperature, TMIN is increased, reducing the fan speed.
CODE
Short Cycle
Long Cycle
000
001
010
011
100
101
110
111
8 cycles (1 s)
16 cycles (2 s)
32 cycles (4 s)
64 cycles (8 s)
128 cycles (16 s)
256 cycles (32 s)
512 cycles (64 s)
1024 cycles (128 s)
16 cycles (2 s)
32 cycles (4 s)
64 cycles (8 s)
128 cycles (16 s)
256 cycles (32 s)
512 cycles (64 s)
1024 cycles (128 s)
2048 cycles (256 s)
Care should be taken in choosing the cycle time. A long
cycle time means that the TMIN is not updated very often;
if your system has very fast temperature transients, the
dynamic TMIN control loop will always be lagging. If you
choose a cycle time that is too fast, the full benefit of
changing TMIN may not have been realized and you
change again on the next cycle; in effect you would be
overshooting. It is necessary to carry out some calibration to identify the most suitable response time.
The loop operation is not as simple as described above.
There are a number of conditions governing situations
in which TMIN can increase or decrease.
SHORT CYCLE AND LONG CYCLE
The ADT7460/ADT7463 implement two loops, a short
cycle and a long cycle. The short cycle takes place every
n monitoring cycles. The long cycle takes place every 2n
monitoring cycles. The value of n is programmable for
each temperature channel. The bits are located at the
following register locations:
Remote 1 = CYR1 = Bits <2:0> of Calibration Control
Register 2 (Addr = 0x37)
Local = CYL = Bits <5:3> of Calibration Control Register 2
(Addr = 0x37)
Remote 2 = CYR2 = Bits <7:6> of Calibration Control
Register 2 and Bit 0 of Calibration Control Register 1
(Addr = 0x36)
Rev. 1 | Page 18 of 27 | www.onsemi.com
–18–
REV. 0
AN-613
SHORT CYCLE
Figure 23 displays the steps taken during the short cycle.
WAIT n
MONITORING
CYCLES
CURRENT
TEMPERATURE
MEASUREMENT
T1(n)
OPERATING
POINT
TEMPERATURE
OP1
PREVIOUS
TEMPERATURE
MEASUREMENT
T1 (n–1)
IS T1(n) >
(OP1 – HYS)
NO
DO NOTHING
YES
IS T1(n) – T1(n–1)
0.25 C
YES
DO NOTHING
(i.e., SYSTEM IS
COOLING OFF
OR CONSTANT.)
NO
IS T1(n) – T1(n–1) = 0.5 – 0.75 C
DECREASE TMIN by 1 C
IS T1(n) – T1(n–1) = 1.0 – 1.75 C
DECREASE TMIN by 2 C
IS T1(n) – T1(n–1) > 2.0 C
DECREASE TMIN by 4 C
Figure 23. Short Cycle
LONG CYCLE
Figure 24 displays the steps taken during the long cycle.
WAIT 2n
MONITORING
CYCLES
CURRENT
TEMPERATURE
MEASUREMENT
T1(n)
OPERATING
POINT
TEMPERATURE
OP1
IS T1(n)
OP1
YES
NO
IS T1(n) < LOW TEMP LIMIT
AND
TMIN < HIGH TEMP LIMIT YES
AND
TMIN < OP1
AND
T1(n) > TMIN
NO
Figure 24. Long Cycle
Rev. 1 | Page 19 of 27 | www.onsemi.com
REV. 0
DECREASE TMIN
by 1 C
–19–
INCREASE
TMIN by 1 C
DO NOT
CHANGE
AN-613
AN-613
EXAMPLES
The following are examples of some circumstances that
EXAMPLES
mayfollowing
cause TMINare
to examples
increase orofdecrease
or stay the same.
The
some circumstances
that
Once the temperature exceeds the operating temperature
hysteresisexceeds
(OP – Hys),
the TMIN temperastarts to
Onceless
the the
temperature
the operating
decrease.
This
occurs
during
the
short
cycle;
see
Figure
ture less the hysteresis (OP – Hys), the TMIN starts23.
to
The
rate with
on
the proMIN decreases
decrease.
Thiswhich
occursTduring
the shortdepends
cycle; see
Figure
23.
grammed
value
of n.TMIN
It also
depends
on howonmuch
the
The rate with
which
decreases
depends
the protemperature
has
increased
between
this
monitoring
grammed value of n. It also depends on how much the
cycle
and the has
last monitoring
cycle, i.e.,this
if the
temperatemperature
increased between
monitoring
ture
has
increased
by
1°C,
then
T
is
reduced
by 2°C.
MIN
cycle and the last monitoring cycle, i.e., if the temperaDecreasing
T
has
the
effect
of
increasing
the
fan
MIN
ture has increased by 1°C, then TMIN is reduced by 2°C.
speed,
thus
providing
more
cooling
to
the
system.
Decreasing TMIN has the effect of increasing the fan
may cause TMIN to increase or decrease or stay the same.
NORMAL OPERATION—NO T MIN ADJUSTMENT
1. If measured
temperature
exceeds the proNORMAL
OPERATION—NO
T MINnever
ADJUSTMENT
grammed
operating
point–hysteresis
temperature,
1. If
measured
temperature
never exceeds
the prothen TMIN isoperating
not adjusted,
i.e., remains at
its current
grammed
point–hysteresis
temperature,
setting.
then
TMIN is not adjusted, i.e., remains at its current
setting.
2. If
measured temperature never drops below the low
temperature
limit, then TMIN
is not
adjusted.
2. If measured temperature
never
drops
below the low
temperature limit, then TMIN is not adjusted.
speed,
thus providing
more
cooling
to the system.
If the temperature
is only
slowly
increasing
in the range
(OP
Hys), i.e., ≤ 0.25°C
per
shortincreasing
monitoringincycle,
then
If
the– temperature
is only
slowly
the range
TMIN–does
This
allows
small changes
in
(OP
Hys),not
i.e., decrease.
≤ 0.25°C per
short
monitoring
cycle, then
temperature
in
the
desired
operating
zone
without
T
does
not
decrease.
This
allows
small
changes
in
MIN
changing TMINin
. The
cycle makes
no change
to TMIN
temperature
thelong
desired
operating
zone without
in
the temperature
(OP –makes
Hys) since
the temperachanging
TMIN. The range
long cycle
no change
to TMIN
ture
has
not exceeded
the(OP
operating
in
the
temperature
range
– Hys) temperature.
since the tempera-
THERM LIMIT
HIGH TEMP
THERM
LIMIT
LIMIT
HIGH TEMP
OPERATING
LIMIT
POINT
OPERATING
POINT
LOW TEMP
LIMIT
LOW TEMP
TMIN
LIMIT
HYSTERESIS
HYSTERESIS
ACTUAL
TEMP
ACTUAL
TEMP
ture
exceeded the
operating
temperature.
Oncehas
thenot
temperature
exceeds
the operating
temperature,
the
long
cycle
will
cause
T
to
reduce
by 1°C
MIN
Once the temperature exceeds the operating temperaevery
long
cycle
while
the
temperature
remains
above
ture, the long cycle will cause TMIN to reduce by
1°C
the
operating
temperature.
This
takes
place
in
addition
every long cycle while the temperature remains above
to
decreasetemperature.
in TMIN that would
occurplace
due to
short
thethe
operating
This takes
in the
addition
cycle.
In
Figure
26,
since
the
temperature
is
only
increasto the decrease in TMIN that would occur due to the short
ing
at In
a rate
less26,
than
or the
equal
to 0.25°C per
short
cycle,
cycle.
Figure
since
temperature
is only
increasno
reduction
in
T
takes
place
during
the
short
cycle.
MIN
ing at a rate less than or equal to 0.25°C per short cycle,
TMIN Temperature between Operating Point and
Figure 25.
Low
Temperature
Limit between Operating Point and
Figure 25. Temperature
Low Temperature
Limit
Since
neither the operating
point–hysteresis temperature nor
thethelow
temperature
limit has
been
Since
neither
operating
point–hysteresis
temperaexceeded,
valuetemperature
is not adjusted
and the
runs
ture
nor the
theTMINlow
limit
hasfanbeen
at a speed the
determined
TMINand
andthe
TRANGE
valexceeded,
TMIN valuebyisthe
not fixed
adjusted
fan runs
ues
in the automatic
speed
mode.
at a defined
speed determined
by thefan
fixed
TMINcontrol
and TRANGE
val-
no reduction
in TMIN takes
during
thethe
short
cycle.
Once
the temperature
hasplace
fallen
below
operating
temperature,
TMIN stays the
Even
when
theoperating
temperaOnce
the temperature
hassame.
fallen
below
the
ture
starts to increase
slowly,
TMINEven
stayswhen
the same
because
temperature,
TMIN stays
the same.
the temperathe temperature
increases
at aTrate
≤
0.25°C
per
cycle.
ture
starts to increase
slowly,
stays
the
same
because
MIN
ues defined in the automatic fan speed control mode.
OPERATING POINT EXCEEDED—T MIN REDUCED
When the measured
temperature MIN
is below
the operating
OPERATING
POINT EXCEEDED—T
REDUCED
point the
temperature
the hysteresis,
remains
MINoperating
When
measured less
temperature
is below T
the
the
same.
point
temperature less the hysteresis, TMIN remains
the temperature increases at a rate ≤ 0.25°C per cycle.
the same.
THERM
LIMIT
HIGHTHERM
TEMP
LIMIT
LIMIT
HIGH TEMP
OPERATING
LIMIT
POINT
OPERATING
POINT
HYSTERESIS
HYSTERESIS
ACTUAL
TEMP
ACTUAL
TEMP
NO CHANGE IN TMIN HERE
DUE TO ANY CYCLE SINCE
NO CHANGE
IN TMIN
T1(n)
– T1 (n–1)
0.25HERE
C
AND TO
T1(n)
< OP
= > TMIN
DUE
ANY
CYCLE
SINCE
T1(n)
– T1
(n–1)
STAYS
THE
SAME0.25 C
AND T1(n) < OP = > TMIN
STAYS THE SAME
TMIN
TMIN
LOW TEMP
LIMIT
LOW TEMP
LIMIT
Figure 26.
DECREASE HERE DUE TO
DECREASE HERE DUE TO
SHORT CYCLE ONLY
LONG CYCLE ONLY
T1(n) – T1 (n–1)
0.5 C
0.25 TO
C
T1(n) – T1 (n–1)
DECREASE
HERE=DUE
TO
DECREASE
HERE DUE
OR
0.75
C
=
>
T
AND
T1(n)
> OP =
> TMIN
SHORT CYCLE ONLY
LONG
CYCLE
ONLY
MIN
T1(n)
– T1 (n–1)BY
= 0.5
0.25
T1(n)
–
T1
(n–1)
DECREASES
1 CC
DECREASES BY 1 C C
OR 0.75
C = >CYCLE
TMIN
AND
T1(n)
> OP CYCLE
= > TMIN
EVERY
SHORT
EVERY
LONG
DECREASES BY 1 C
DECREASES BY 1 C
EVERY
SHORT CYCLE OperatingEVERY
CYCLE
Effect
of Exceeding
PointLONG
– Hysteresis
Temperature
Figure 26. Effect of Exceeding
Operating Point – Hysteresis Temperature
Rev. 1 | Page 20 of 27 | www.onsemi.com
–20–
REV. 0
–20–
REV. 0
AN-613
Figure 27 shows how TMIN increases when the current temperature is above TMIN and below the low temperature
limit, and TMIN is below the high temperature limit and
below the operating point. Once the temperature rises
above the low temperature limit, TMIN stays the same.
INCREASE T MIN CYCLE
When the temperature drops below the low temperature
limit, TMIN can increase in the long cycle. Increasing TMIN
has the effect of running the fan slower and therefore
quieter. The long cycle diagram in Figure 24 shows the
conditions that need to be true for TMIN to increase. Here
is a quick summary of those conditions and the reasons
they need to be true.
WHAT PREVENTS T MIN FROM REACHING FULL SCALE?
Since TMIN is dynamically adjusted, it is undesirable for
TMIN to reach full scale (127°C) because the fan would
never switch on. As a result, TMIN is allowed to vary only
within a specified range:
TMIN can increase if
1. The measured temperature has fallen below the low
temperature limit. This means the user must choose
the low limit carefully. It should not be so low that the
temperature will never fall below it because TMIN
would never increase and the fans would run faster
than necessary.
1. The lowest possible value to TMIN is –127°C.
2. TMIN cannot exceed the high temperature limit.
3. If the temperature is below TMIN, the fan is switched
off or is running at minimum speed and dynamic TMIN
control is disabled.
AND
THERM
LIMIT
2. TMIN is below the high temperature limit. TMIN is never
allowed to increase above the high temperature limit.
As a result, the high limit should be sensibly chosen
because it determines how high TMIN can go.
OPERATING
POINT
LOW TEMP
LIMIT
AND
TMIN
4. The temperature is above TMIN. The dynamic TMIN
control is turned off below TMIN.
THERM
LIMIT
HIGH TEMP
LIMIT
HYSTERESIS
ACTUAL
TEMP
TMIN
Figure 27. Increasing TMIN for Quieter Operation
Rev. 1 | Page 21 of 27 | www.onsemi.com
REV. 0
TMIN PREVENTED
FROM INCREASING
Figure 28. TMIN Adjustments Limited by the High
Temperature Limit
AND
LOW TEMP
LIMIT
ACTUAL
TEMP
HIGH TEMP
LIMIT
3. TMIN is below the operating point temperature. TMIN
should never be allowed to increase above the operating point temperature since the fans would not switch
on until the temperature rose above the operating point.
OPERATING
POINT
HYSTERESIS
–21–
AN-613
STEP 10: DETERMINING WHETHER TO MONITOR THERM
Using the operating point limit ensures that the dynamic
TMIN control mode is operating in the best possible
acoustic position while ensuring that the temperature
never exceeds the maximum operating temperature.
Using the operating point limit allows the TMIN to be
independent of system level issues because of its selfcorrective nature.
PHTL = 0 ignores any THERM assertions. The local temperature operating point register will reflect its
programmed value.
<4> PHTR1 = 1 copies the Remote 1 current temperature
to the Remote 1 operating point register if THERM gets
asserted. The operating point will contain the temperature at which THERM is asserted. This allows the system
to run as quietly as possible without affecting system
performance.
In PC design, the operating point for the chassis is usually the worst-case internal chassis temperature.
PHTR1 = 0 ignores any THERM assertions. The Remote 1
operating point register will reflect its programmed
value.
The optimal operating point for the processor is determined by monitoring the thermal monitor in the Intel
Pentium® 4 processor. To do this, the PROCHOT output
of the Pentium 4 is connected to the THERM input of the
ADT7460/ADT7463.
ENABLING DYNAMIC T MIN CONTROL MODE
Bits <7:5> of dynamic TMIN control Register 1 (Reg. 0x36)
enable/disable dynamic TMIN control on the temperature
channels.
The operating point for the processor can be determined
by allowing the current temperature to be copied to the
operating point register when the PROCHOT output
pulls the THERM input low on the ADT7460/ADT7463.
This gives the maximum temperature at which the
Pentium 4 can be run before clock modulation occurs.
DYNAMIC T MIN CONTROL REGISTER 1 (0x36)
<5> R2T = 1 enables dynamic TMIN control on the Remote 2
temperature channel. The chosen TMIN value will be
dynamically adjusted based on the current temperature,
operating point, and high and low limits for this zone.
ENABLING THERM TRIP POINT AS THE OPERATING
POINT
Bits <4:2> of dynamic TMIN control Register 1 (Reg. 0x36)
enable/disable THERM monitoring to program the operating point.
R2T = 0 disables dynamic TMIN control. The TMIN value
chosen will not be adjusted and the channel will behave
as described in the Automatic Fan Control section.
<6> LT = 1 enables dynamic TMIN control on the local
temperature channel. The chosen TMIN value will be
dynamically adjusted based on the current temperature,
operating point, and high and low limits for this zone.
DYNAMIC T MIN CONTROL REGISTER 1 (0x36)
<2> PHTR2 = 1 copies the Remote 2 current temperature
to the Remote 2 operating point register if THERM gets
asserted. The operating point will contain the temperature at which THERM is asserted. This allows the system
to run as quietly as possible without system performance being affected.
LT = 0 disables dynamic TMIN control. The TMIN value chosen will not be adjusted and the channel will behave as
described in the Automatic Fan Control section.
<7> R1T = 1 enables dynamic TMIN control on the Remote 1
temperature channel. The chosen TMIN value will be
dynamically adjusted based on the current temperature,
operating point, and high and low limits for this zone.
PHTR2 = 0 ignores any THERM assertions. The Remote 2
operating point register will reflect its programmed
value.
<3> PHTL = 1 copies the local current temperature to the
local temperature operating point register if THERM
gets asserted. The operating point will contain the temperature at which THERM is asserted. This allows the
system to run as quietly as possible without system performance being affected.
R1T = 0 disables dynamic TMIN control. The TMIN value
chosen will not be adjusted and the channel will behave
as described in the Automatic Fan Control section.
Rev. 1 | Page 22 of 27 | www.onsemi.com
–22–
REV. 0
AN-613
ENHANCING SYSTEM ACOUSTICS
Automatic fan speed control mode reacts instantaneously to changes in temperature, i.e., the PWM duty
cycle will respond immediately to temperature change.
Any impulses in temperature can cause an impulse in
fan noise. For psycho-acoustic reasons, the ADT7460/
ADT7463 can prevent the PWM output from reacting
instantaneously to temperature changes. Enhanced
acoustic mode will control the maximum change in
PWM duty cycle in a given time. The objective is to prevent the fan from cycling up and down and annoying the
system user.
THE APPROACH
There are two different approaches to implementing
system acoustic enhancement. The first method is
temperature-centric. It involves “smoothing” transient
temperatures as they are measured by a temperature
source, e.g., Remote 1 temperature.
The temperature values used to calculate the PWM duty
cycle values would be smoothed, reducing fan speed
variation. However, this approach would cause an inherent delay in updating fan speed and would cause the
thermal characteristics of the system to change. It would
also cause the system fans to stay on longer than necessary, since the fan’s reaction is merely delayed. The user
would also have no control over noise from different
fans driven by the same temperature source. Consider
controlling a CPU cooler fan (on PWM1) and a chassis
fan (on PWM2) using Remote 1 temperature. Because
the Remote 1 temperature is smoothed, both fans would
be updated at exactly the same rate. If the chassis fan is
much louder than the CPU fan, there is no way to
improve its acoustics without changing the thermal solution of the CPU cooling fan.
ACOUSTIC ENHANCEMENT MODE OVERVIEW
Figure 29 gives a top-level overview of the automatic fan
control circuitry on the ADT7460/ADT7463 and where
acoustic enhancement fits in. Acoustic enhancement is
intended as a post-design “tweak” made by a system or
mechanical engineer evaluating best settings for the
system. Having determined the optimal settings for the
thermal solution, the engineer can adjust the system
acoustics. The goal is to implement a system that is
acoustically pleasing without causing user annoyance
due to fan cycling. It is important to realize that although
a system may pass an acoustic noise requirement spec,
(e.g., 36 dB), if the fan is annoying, it will fail the consumer test.
The second approach is fan-centric. The idea is to control the PWM duty cycle driving the fan at a fixed rate,
e.g., 6%. Each time the PWM duty cycle is updated, it is
incremented by a fixed 6%. As a result, the fan ramps
ACOUSTIC
ENHANCEMENT
PWM
CONFIG
PWM
MIN
THERMAL CALIBRATION
100%
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
REMOTE 2 =
CPU TEMP
TMIN
TRANGE
TACHOMETER 1
MEASUREMENT
0%
THERMAL CALIBRATION
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
MUX
TMIN
TRANGE
0%
100%
TMIN
TRANGE
PWM
GENERATOR
TACHOMETER 3
AND 4
MEASUREMENT
0%
PWM2
TACH2
PWM
GENERATOR
PWM3
TACH3
Figure 29. Acoustic Enhancement Smooths Fan Speed Variations under Automatic Fan Speed Control
Rev. 1 | Page 23 of 27 | www.onsemi.com
REV. 0
–23–
FRONT
CHASSIS
PWM
CONFIG
PWM
MIN
RAMP CONTROL
(ACOUSTIC
ENHANCEMENT)
REMOTE 1 =
AMBIENT TEMP
CPU
FAN SINK
TACH1
TACHOMETER 2
MEASUREMENT
THERMAL CALIBRATION
PWM1
PWM
CONFIG
PWM
MIN
100%
LOCAL =
VRM TEMP
PWM
GENERATOR
REAR
CHASSIS
AN-613
AN-613
AN-613
AN-613
smoothly to its newly calculated speed. If the temperaAN-613
smoothly to its newly calculated speed. If the temperature
startstotoitsdrop,
PWM duty
cycle
immediately
smoothly
newlythe
calculated
speed.
If the
tempera-
ture
startstotoitsdrop,
the
PWM duty
cycle
immediately
smoothly
newly
calculated
speed.
If the
temperadecreases
6%
every
update.
the
fan
ramps
ture
starts by
to drop,
the PWM
dutySo
cycle
decreases
by
6% every
update.
So
theimmediately
fan ramps
ture
starts
to
drop,
the
PWM
duty
cycle
immediately
smoothly
up
or
down
without
inherent
system
delay.
smoothly
to
its
newly
calculated
speed.
If
the
temperadecreases
byor6%
every
update.
So the
fan ramps
smoothly up
down
without
inherent
system
delay.
by
6%
every
update.
So cooler
the
fanfan
ramps
Consider
controlling
the
same
CPU
(on
turedecreases
starts
to
drop,
the
PWM
duty
cycle
immediately
smoothly
or down the
without
systemfan
delay.
Consider up
controlling
sameinherent
CPU cooler
(on
smoothly
up
or
down
without
inherent
system
delay.
PWM1)
and
chassis
fan
(on
PWM2)
using
Remote
1
temdecreases
by
6%
every
update.
So
the
fan
ramps
Consider
controlling
same CPU
fan
(on
PWM1) and
chassis fanthe
(on PWM2)
usingcooler
Remote
1 temConsider
controlling
the
same
CPU
cooler
fan
(on
perature.
The
TMIN fan
and(on
TRANGE
settings
havedelay.
already
smoothly
up
orchassis
down
without
inherent
system
PWM1)
and
PWM2)
using
Remote
1
temperature.
The
TMIN fan
and(on
TRANGE
settings
have already
PWM1)
and
chassis
PWM2)
using
Remote
1
tembeen defined
fan speed
control
mode,
Consider
controlling
the same
CPU
cooler
fan
(oni.e.,
perature.
Thein
Tautomatic
settings
have
already
MIN and TRANGE
been defined
fan speed
control
mode,
i.e.,
perature.
TheinTautomatic
andPWM2)
T
settings
have
already
MIN
RANGE
thermal
characterization
of
the
control
loop
has
been
PWM1)
and
chassis
fan
(on
using
Remote
1
tembeen
defined
in automaticoffan
control
i.e.,
thermal
characterization
thespeed
control
loopmode,
has been
been
defined
in
automatic
fan
speed
control
mode,
i.e.,
optimized.
Now
fan
is
noisier
than
the been
CPU
perature.
The
TMIN the
andchassis
TRANGE
settings
have
already
thermal
characterization
of
the
control
loop
has
optimized.
Now the chassis
fan
is
noisierloop
thanhas
the been
CPU
thermal
characterization
of
the
control
cooling
fan.
So the
PWM2
can
beis placed
into
been
defined
in
automatic
fan
speed
control
i.e.,
optimized.
Now
chassis
noisier mode,
than acoustic
the
CPU
cooling fan.
So the
PWM2
canfan
beis placed
into
acoustic
optimized.
Now
chassis
fan
noisier
than
the
CPU
enhancement
mode
independently
of
PWM1.
The
thermal
characterization
of
the
control
loop
has
been
cooling
fan.
So
PWM2
can
be
placed
into
acoustic
enhancement
mode
independently
of into
PWM1.
The
cooling
fan.
So
PWM2
can
be
placed
acoustic
acoustics
of
the
chassis
fan
can
therefore
be
adjusted
optimized.
Now
the
chassis
fan
is
noisier
than
the
CPU
enhancement
independently
of PWM1.
The
acoustics of themode
chassis
fan can therefore
be adjusted
enhancement
mode
independently
of
PWM1.
The
without
affecting
the
acoustic
behavior
ofinto
the CPU
cooling
cooling
fan.
Sothe
PWM2
canfanbe
placed
acoustic
acoustics
of
chassis
can
therefore
be
adjusted
without affecting
the
acoustic
behavior
of the CPU
cooling
acoustics
of
the
chassis
fan
can
therefore
be
adjusted
fan,
even
though
fansbehavior
are being
controlled
enhancement
mode
independently
ofof PWM1.
The by
without
affecting
theboth
acoustic
the
CPU cooling
fan, even
though
fansbehavior
are being
controlled
by
without
affecting
theboth
acoustic
of the
CPU
cooling
Remote
1
temperature.
This
is
exactly
how
acoustic
acoustics
of
the
chassis
fan
can
therefore
be
adjusted
fan,
even1 though
both fans
being controlled
by
Remote
temperature.
This are
is exactly
how acoustic
fan,
even
though
both
fans
are
being
controlled
by
enhancement
works
on the
ADT7460/ADT7463.
without
affecting
the
acoustic
behavior
of the CPU
cooling
Remote
1
temperature.
This
is
exactly
how
acoustic
enhancement
works on the
ADT7460/ADT7463.
Remote
1
temperature.
This
is
exactly
how
acoustic
fan,enhancement
even thoughworks
bothon
fans
being controlled by
the are
ADT7460/ADT7463.
enhancement
works on
the ADT7460/ADT7463.
ENABLING
ACOUSTIC
ENHANCEMENT
PWM
Remote
1 temperature.
This
is exactly FOR
howEACH
acoustic
ENABLING ACOUSTIC ENHANCEMENT FOR EACH PWM
OUTPUT
enhancement
works
on
the
ADT7460/ADT7463.
ENABLING
ACOUSTIC ENHANCEMENT FOR EACH PWM
OUTPUT
ENABLING
ACOUSTIC ENHANCEMENT
FOR
EACH PWM
ENHANCE
ACOUSTICS
REGISTER 1 (Reg.
0x62)
OUTPUT
ENHANCE
ACOUSTICS REGISTER 1 (Reg. 0x62)
OUTPUT
<3>
= 1 Enables
acoustic
enhancement
onEACH
PWM1
output.
ENABLING
ACOUSTIC
ENHANCEMENT
FOR
PWM
ENHANCE
ACOUSTICS
1 (Reg.
<3>
= 1 Enables
acousticREGISTER
enhancement
on 0x62)
PWM1 output.
ENHANCE
ACOUSTICS
REGISTER
1 (Reg.
0x62)
OUTPUT
<3> = 1 Enables acoustic enhancement on PWM1 output.
<3>
= 1 ACOUSTICS
Enables
acoustic
enhancement
on 0x63)
PWM1 output.
ENHANCE
ACOUSTICS
REGISTER
2 (Reg.
ENHANCE
REGISTER
1 (Reg.
0x62)
ENHANCE ACOUSTICS REGISTER 2 (Reg. 0x63)
1 Enables
acoustic
enhancement
on
PWM2
output.
<3><7>
= 1 =Enables
acoustic
enhancement
PWM1
output.
ENHANCE
ACOUSTICS
2 on
(Reg.
<7>
= 1 Enables
acousticREGISTER
enhancement
on 0x63)
PWM2 output.
ENHANCE
ACOUSTICS
REGISTER
2 (Reg.
0x63)
<7> =
=1
1 Enables
Enables acoustic
acoustic enhancement
enhancement on
on PWM3
PWM2 output.
output.
<3>
<7>
Enables
enhancement
on
ENHANCE
<3> =
=1
1 ACOUSTICS
Enables acoustic
acoustic
REGISTER
enhancement
2 (Reg. 0x63)
on PWM2
PWM3 output.
output.
=Enables
1 Enables
acoustic
enhancement
on
PWM3
output.
<7><3>
=
1
acoustic
enhancement
on
PWM2
output.
<3> = 1 Enables
acoustic
enhancement
PWM3 output.
EFFECT
OF RAMP
RATE ON
ENHANCEDon
ACOUSTICS
EFFECT OF RAMP RATE ON ENHANCED ACOUSTICS
<3>MODE
= 1 Enables
acoustic
enhancement
on PWM3
output.
EFFECT
OF RAMP
RATE
ON ENHANCED
ACOUSTICS
MODE
EFFECT
OF signal
RAMP driving
RATE ONthe
ENHANCED
ACOUSTICS
The
PWM
fan will have
a period, T,
MODE
The
PWM signal driving the fan will have a period, T,
MODE
given
byRAMP
the
PWM
drive
frequency,
f,ACOUSTICS
since
=period,
1/f. ForT,
a
EFFECT
OF
RATE
ON ENHANCED
The
PWM
signal
the fan will
have T
given
by the
PWMdriving
drive frequency,
f, since
Ta
=period,
1/f. ForT,
a
The
PWM
signal
driving
the
fan
will
have
a
given
PWM
period,
T,
the
PWM
period
is
subdivided
into
MODE
given
by theperiod,
PWM drive
frequency,
f, since
T = 1/f. For
a
given
PWM
T,
the
PWM
period
is
subdivided
into
given
bysignal
the
PWM
drive
frequency,
f,corresponds
since
T = 1/f.to
For
a
equal
time
slots.
One
timewill
slothave
the
The255
PWM
driving
the
fan
a period,
T,into
given
PWM
period,
T,
the
PWM
period
is
subdivided
255
equal
time
slots.
OnePWM
timeperiod
slot corresponds
to into
the
given
PWM
period,
T,
the
is
subdivided
smallest
possible
increment
in
PWM
duty
cycle.
A
PWM
given
by
the PWM
frequency,
f, since
T = 1/f. For athe
255
equal
time drive
slots.
One time
slot
corresponds
smallest
possible
increment
in PWM
duty cycle. Ato
PWM
255PWM
equal
timeduty
slots.
One
time
slot
to
the
signal
of period,
33%
cycle
will
thus
be
highcycle.
for 1/3Ainto
�
255
given
T,increment
the
PWM
period
iscorresponds
subdivided
smallest
possible
in
PWM
duty
PWM
signal
of
33%
duty
cycle
will
thus
be
high
for
1/3
�
255
smallest
possible
increment
in
PWM
duty
cycle.
A
PWM
time
slots
and
low
for
2/3
�
255
time
slots.
Therefore,
255signal
equalof
time
slots. One
time
slot corresponds
to the
33%
will
be high
forTherefore,
1/3
� 255
time
slots
andduty
low cycle
for 2/3
� thus
255 time
slots.
signal
of 33%
duty
cycle
will
thus
beahigh
forthat
1/3
255
33%
PWM
duty
cycle
corresponds
to
signal
is�high
smallest
possible
increment
in�PWM
duty
cycle.
A
PWM
time
slots
and
low
for
2/3
255
time
slots.
Therefore,
33%
PWM
duty
cyclefor
corresponds
to a signal
that
is high
time
slots
and
low
2/3
�
255
time
slots.
Therefore,
for
85
time
slots
and
low
for
170
time
slots.
signal
ofPWM
33%duty
dutycycle
cyclecorresponds
will thus be to
high
for 1/3
� is
255
33%
a slots.
signal
that
high
for
85
timeduty
slotscycle
and corresponds
low for 170 time
33%
PWM
to slots.
a signal
that is high
time
andslots
low for
255
time
forslots
85 time
and2/3
low�for
170
time
slots.Therefore,
for
85 time
low for 170
slots.
33%
PWM
dutyslots
cycleand
corresponds
totime
a signal
that is high
PWM_OUT
33% DUTY
PWM_OUT
for 85
time
slots
and
low
for
170
time
slots.
CYCLE
33%
DUTY
PWM_OUT
PWM_OUT
33%CYCLE
DUTY
33%CYCLE
DUTY
CYCLE
PWM_OUT
33% DUTY
CYCLE
170
TIME170
SLOTS
TIME170
SLOTS
PWM OUTPUT170
TIME SLOTS
(ONE
PWM PERIOD)
OUTPUT
TIME SLOTS
= 255
TIME
SLOTS
(ONE
PERIOD)
PWM
OUTPUT
170
85
= 255
TIME
SLOTS
PWM
OUTPUT
(ONE
PERIOD)
TIME
SLOTS
TIME SLOTS
(ONE
PERIOD)
= 255
TIME
SLOTS
= 255
TIMECycle
SLOTS Represented
30. 33% PWM
Duty
PWM
OUTPUT
85
TIME 85
SLOTS
TIME 85
SLOTS
TIME 85
SLOTS
TIME SLOTS
READ
TEMPERATURE
READ
TEMPERATURE
READ
READ
TEMPERATURE
TEMPERATURE
CALCULATE
READ
NEW PWM
CALCULATE
TEMPERATURE
DUTY
NEWCYCLE
PWM
CALCULATE
DUTY
CALCULATE
NEWCYCLE
PWM
NEWCYCLE
PWM
DUTY
DUTY
CYCLE
CALCULATE
Figure
Figure 31.BYEnhanced
Acoustics Algorithm
RAMP
Figure 31.
Enhanced
Acoustics
Algorithm
RATE
The enhanced
acoustics
mode
algorithm
calculates a
Figure
31.
Enhanced
Acoustics
Algorithm
The enhanced acoustics mode
algorithm
calculates a
new
PWM
duty
cycle
based
on
the
temperature
meaThe
enhanced
acoustics
mode
algorithm
calculates
a
new
PWM
duty
cycle
based
on
the
temperature
meaFigure
31.
Enhanced
Acoustics
Algorithm
The enhanced
acoustics
mode
algorithm
calculates
a
sured.
If
the
new
PWM
duty
cycle
value
is
greater
than
new
PWM
duty
cycle
based
on
the
temperature
measured.
If theduty
newcycle
PWMbased
duty cycle
value
is greater meathan
new
PWM
on
the
temperature
the
previous
PWM
value,
the
previous
PWM
duty
cycle
Thesured.
enhanced
mode
algorithm
calculates
a
If the acoustics
new
duty
valuePWM
is greater
than
the
previous
PWMPWM
value,
thecycle
previous
duty cycle
sured.
the new
PWM
value
is greater
than
value
isIf incremented
byduty
either
1, 2,temperature
3, 5,PWM
8,
12,duty
24,
or
48
new
PWM
duty
cycle
based
oncycle
the
meathe
previous
PWM
value,
the
previous
cycle
value
is incremented
by either
1, 2, 3, 5,PWM
8, 12,duty
24, or
48
the
previous
PWM
value,
the
previous
cycle
time
slots,
depending
on
the
settings
of
the
enhance
sured.
If the
new PWM duty
cycle 1,
value
greater
than
value
is incremented
byon
either
2, 3, is
5,of
8, the
12, 24,
or 48
time
slots,
depending
the
settings
enhance
value
is incremented
either
1, 2, 3,
5, 8,cycle
12, 24,
or 48
If by
the
duty
value
is
theacoustics
previous
PWM
value,
the
previous
PWM
duty
cycle
time
slots,registers.
depending
onnew
the PWM
settings
of cycle
the enhance
acoustics
registers.
If the
new
PWM
duty
value is
time
slots,
depending
on
the
settings
of
the
enhance
less
than
the
previous
PWM
value,
the
previous
PWM
value
is incremented
byIf either
1, 2,
3, 5,duty
8, 12,
24, or
48 is
acoustics
the
new
PWM
cycle
value
less
than registers.
the previous
PWM
value,
the
previous
PWM
acoustics
registers.
Ifonthe
new
PWM
duty
cycle
value
is
duty
cycle
is decremented
by
1,
2, 3,the
8,
12,
24,
or 48
time
slots,
depending
the
settings
of5, the
enhance
less
than
the
previous
PWM
value,
previous
PWM
duty
cyclethe
is decremented
by value,
1, 2, 3,the
5, 8,
12, 24, PWM
or 48
less
than
previous
PWM
previous
time
slots.
Each
time
the
PWM
duty
cycle
is
incremented
acoustics
registers.
If the new by
PWM
value
is 48
duty
cycle
is decremented
1, 2,duty
3, 5,cycle
8,
12,
24, or
time
slots.
Each
time the PWM
cycle
is incremented
duty
cycle
is
decremented
byasduty
1,the
2,
3,
5, 8,
12,PWM
24,
or
48
decremented,
it isPWM
stored
previous
duty
lessor
than
the Each
previous
value,
the
previous
PWM
time
slots.
time
the
PWM
duty
cycle
is
incremented
or
decremented,
it isthe
stored
asduty
the cycle
previous
PWM duty
time
slots.
Each
time
PWM
is
incremented
cycle
for
the
next
comparison.
duty
cycle
is decremented
by 1,as2,the
3, 5,
8, 12, 24,
or 48
or
decremented,
is stored
previous
PWM
duty
cycle
for the next it
comparison.
orslots.
decremented,
is PWM
storedduty
as the
previous
PWM duty
time
Each
timeitcomparison.
the
cycle
is incremented
cycle
for
the
next
A
ramp
1 corresponds
to one time slot, which is
cycle
forrate
the of
next
comparison.
A ramp
rate
of
to previous
one time PWM
slot, which
or decremented,
it1iscorresponds
stored as the
duty is
1/255
of
the
PWM
period.
In
enhanced
acoustics
mode,
A
ramp
rate
of comparison.
1 corresponds
to one time
slot, which
is
1/255
the
PWM
period. In enhanced
acoustics
mode,
cycle
for of
the
next
A
ramp
rate
of
1
corresponds
to
one
time
slot,
which
is
incrementing
or
decrementing
by
1
changes
the
PWM
1/255
of
the
PWM
period.
In
enhanced
acoustics
mode,
incrementing
or decrementing
by 1 changes
themode,
PWM
1/255
of
the
PWM
period.
In
enhanced
acoustics
output
byof
1/255
�decrementing
100%. to one
A ramp
rate
1 or
corresponds
slot, which
is
incrementing
by time
1 changes
the PWM
output by 1/255
�decrementing
100%.
incrementing
orperiod.
by 1 acoustics
changes the
PWM
1/255
of
the
PWM
In
enhanced
mode,
output by 1/255 � 100%.
output
byDETERMINING
1/255
� 100%.THE RAMP
STEP 11:
RATE FOR
incrementing
or decrementing
by 1 changes
the PWM
STEP 11: DETERMINING THE RAMP RATE FOR
ACOUSTIC
ENHANCEMENT
output
by
1/255
�
100%.
STEP
11: DETERMINING
THE RAMP RATE FOR
ACOUSTIC
ENHANCEMENT
STEP
11: DETERMINING
THE
RAMP enhancement
RATE FOR
The
optimal
ramp rate for
acoustic
can be
ACOUSTIC
ENHANCEMENT
The
optimalENHANCEMENT
ramp rate for acoustic enhancement can be
ACOUSTIC
found
through
system
characterization
after
the
thermal
STEP
11:
DETERMINING
THE
RAMP
RATE
FOR
The
optimal
ramp
rate characterization
for acoustic enhancement
can be
found
through
system
after the thermal
The
optimal
ramp
rate finished.
for acoustic
can
be
optimization
has
been
Theenhancement
effect
ofthe
each
ramp
ACOUSTIC
ENHANCEMENT
found
through
system
characterization
after
thermal
optimization
has
been characterization
finished. The effect
ofthe
each
ramp
found
through
system
after
thermal
should
be
logged,
if
possible,
toeffect
determine
thebe
best
Therate
optimal
ramp
rate
for finished.
acoustic
enhancement
can
optimization
has
been
The
of each
rate
should be
logged,
if possible,
toeffect
determine
theramp
best
optimization
has
been
finished.
The
of thermal
each
ramp
setting
for
a
given
solution.
found
through
system
characterization
after
the
rate
should
logged,
if possible, to determine the best
setting
for abe
given
solution.
rate
should
be
logged,
if
possible,
to
determine
the
best
optimization
beensolution.
finished. The effect of each ramp
setting forhas
a given
setting
for
a
given
solution.
REGISTER
(Reg. 0x62)
rateENHANCE
should beACOUSTICS
logged, if possible,
to1determine
the best
ENHANCE ACOUSTICS REGISTER 1 (Reg. 0x62)
<2:0>
ACOU
Select
the
Ramp
Rate
for
PWM1.
setting
for
a
given
solution.
ENHANCE
ACOUSTICS
(Reg.
0x62)
<2:0>
ACOU
Select the REGISTER
Ramp Rate1
PWM1.
ENHANCE
ACOUSTICS
REGISTER
1 for
(Reg.
0x62)
000
=Select
1 Time
Slot
= 35Rate
seconds
<2:0> ACOU
the
Ramp
for
PWM1.
000 =Select
1 Time
Slot
= 35Rate
seconds
<2:0>
ACOU
the
Ramp
for
PWM1.
001
=2
Time
Slots
17.6
seconds
ENHANCE ACOUSTICS
REGISTER
1seconds
(Reg.
0x62)
000
1
Time
Slot
==
001 =
=
2
Time
Slots
=35
17.6
seconds
=
1
Time
Slot
=Rate
35
seconds
010
=
3
Time
Slots
=
11.8
seconds
<2:0> ACOU000
Select
the
Ramp
for
PWM1.
001
Time
Slots
seconds
010 =
=2
3
Time
Slots =
= 17.6
11.8
seconds
2
Time
17.6
seconds
011
=
5
Time
Slots
=
7
seconds
000001
= 1=
Time
SlotSlots
= 35=
seconds
010
=
3
Time
Slots
=
11.8
seconds
011
=
5
Time
Slots
=
7
seconds
010
=
3
Time
Slots
=
11.8
seconds
8
Time
Slots
=
4.4
seconds
001100
= 2=
Time
Slots
= 17.6
seconds
011
=
5
Time
Slots
=
7
seconds
100
=
8
Time
Slots
=
4.4
seconds
011
=
5
Time
Slots
=
7
seconds
12
Time
=4.4
3seconds
seconds
010101
= 3=Time
SlotsSlots
= 11.8
100
8
Time
seconds
101 =
=
12
TimeSlots
Slots=
=4.4
3 seconds
=
8
Time
Slots
=seconds
seconds
110
=
24
Time
Slots
=
1.6
seconds
011100
=
5
Time
Slots
=
7
101
=
12
Time
Slots
=
3
seconds
110
=
24
Time
Slots
=
1.6
seconds
101
=
12
Time
Slots
=
3
seconds
=
48
Time
Slots
=
0.8
seconds
100111
=
8
Time
Slots
=
4.4
seconds
110
=
24
Time
Slots
=
1.6
seconds
111
=
48
Time
Slots
=
0.8
seconds
110
=
24
Time
Slots
=
1.6
seconds
101111
= 12
Time
Slots
=
3
seconds
= 48 Time Slots = 0.8 seconds
111
=
48
Time
Slots
=
0.8
seconds
110 = 24 Time Slots = 1.6 seconds
111 = 48 Time Slots = 0.8 seconds
Figure
in
Figure
30. 33% PWM
Cycle Represented in
(ONEDuty
PERIOD)
Time Slots
Figure
30.
33%
PWM
Duty
Cycle
Represented
in
= 255 TIME SLOTS
Time Slots
Figure
30. 33% PWM Duty Cycle Represented in
Time
Slots
TheTime
ramp
rates in the enhanced acoustics mode are
Slots
The ramp
ratesPWM
in the
enhanced
acoustics mode
are
Figure
30. from
33%
Duty
Cycle
in 48. The
selectable
1,
2, 3, Represented
5, 8,
12, 24, and
The
ramp
ratesthe
in values
the enhanced
acoustics
mode
are
selectable
the
values
1, 2, 3, 5, 8,
12, 24, and
48. The
Time
Slotsfrom
The
ramp
rates
in
the
enhanced
acoustics
mode
are
ramp
ratesfrom
are actually
discrete
time
slots.
For
example,
selectable
the
values
1,
2,
3,
5,
8,
12,
24,
and
48.
The
ramp ratesfrom
are actually
discrete
time
slots.
For
example,
selectable
the
values
1,
2,
3,
5,
8,
12,
24,
and
48.
The
the
ramp
rate
= the
8, then
eight time
slots
willmode
beexample,
added
Theif
ramp
rates
enhanced
acoustics
are to
ramp
rates
arein
actually
time
slots.
if the ramp
rate
= 8, thendiscrete
eight time
slots
willFor
beexample,
added to
ramp
rates
are
actually
discrete
time
slots.
For
the
PWM
high
duty
cycle
each
time
the
PWM
duty
cycle
selectable
from
the
values
1,
2,
3,
5,
8,
12,
24,
and
48.
The
if
the
ramphigh
rateduty
= 8, then
will beduty
added
to
the
PWM
cycleeight
eachtime
timeslots
the PWM
cycle
if
the
ramp
rate
= 8, then
eight
time
slots
willexample,
be
added
to
needs
to
be
increased.
If
the
PWM
duty
cycle
value
ramp
rates
are
actually
discrete
time
slots.
For
the
PWM
high
duty
cycle
each
time
the
PWM
duty
cycle
needs
to high
be increased.
Ifeach
thetime
PWM
duty
cycle
value
the
PWM
duty
cycle
the
PWM
duty
cycle
needs
to
be
it will
be slots
decreased
eightvalue
time
if the
ramp
= increased.
8, then eight
will
beby
added
to
needs
torate
bedecreased,
If time
the
duty
cycle
needs to
decreased,
it will
be PWM
decreased
by
eightvalue
time
tobe
beduty
increased.
If
the
PWM
dutyduty
cycle
slots.
Figure
31
shows
how
the
enhanced
acoustics
theneeds
PWM
high
cycle
each
time
the
PWM
cycle
needs
be decreased,
will
decreased
by eight
time
slots. to
Figure
31 showsit
howbe
the
enhanced
acoustics
needs
to
be
decreased,
it
will
be
decreased
by
eight
time
mode
operates.
needs
to algorithm
be increased.
If the
PWM
duty cycle acoustics
value
slots.
Figure
31
shows
how
the
enhanced
mode algorithm
operates.
slots.
Figure
31
shows
how
the
enhanced
acoustics
needs
to be
decreased,
it will be decreased by eightRev.
time
mode
algorithm
operates.
1 | Page 24 of
27 | www.onsemi.com
–24–
mode
algorithm
operates.
–24–
slots.
Figure
31 shows
how the enhanced acoustics
–24–
mode algorithm operates.
–24–
–24–
DECREMENT
NEW
PWM PWM
IS NEW
NO
PREVIOUS
DECREMENT
DUTY
VALUE
>
ISCYCLE
NEW PWM
NO
PWM
VALUE
PREVIOUS
DECREMENT
VALUE
>
BY RAMP
PWM
VALUE
ISPREVIOUS
NEW PWM
NO
DECREMENT
PREVIOUS
VALUE?
PREVIOUS
RATE
IS VALUE
NEW PWM
NO
BY RAMP
>
PREVIOUS
PWM
VALUE
VALUE?>
VALUE
RATE
PREVIOUS
PWM
VALUE
BY RAMP
DECREMENT
PREVIOUS
YES
VALUE?
BY
RAMP
RATE
IS NEW PWM
NO
PREVIOUS
VALUE?
RATE
VALUE > YES
PWM VALUE
YES
PREVIOUS
BY RAMP
INCREMENT
YES
VALUE?
RATE
PREVIOUS
INCREMENT
PWM
VALUE
PREVIOUS
INCREMENT
BY
RAMP
PWM
VALUE
YES
INCREMENT
PREVIOUS
BYRATE
RAMP
PREVIOUS
PWM
VALUE
PWM
VALUE
BYRATE
RAMP
INCREMENT
BY
RAMP
RATE
PREVIOUS
RATE
31.
Enhanced
Acoustics Algorithm
PWM VALUE
REV. 0
REV. 0
REV. 0
REV. 0
REV. 0
AN-613
Figure 33 shows how changing the ramp rate from 48 to
8 affects the control loop. The overall response of the
fan is slower. Since the ramp rate is reduced, it takes
longer for the fan to achieve full running speed. In this
case, it took approximately 4.4 seconds for the fan to
reach full speed.
ENHANCE ACOUSTICS REGISTER 2 (Reg. 0x63)
<2:0> ACOU3 Select the ramp rate for PWM3.
000 = 1 Time Slot = 35 seconds
001 = 2 Time Slots = 17.6 seconds
010 = 3 Time Slots = 11.8 seconds
011 = 5 Time Slots = 7 seconds
100 = 8 Time Slots = 4.4 seconds
101 = 12 Time Slots = 3 seconds
110 = 24 Time Slots = 1.6 seconds
111 = 48 Time Slots = 0.8 seconds
120
140
RTEMP
120
100
<6:4> ACOU2 Select the ramp rate for PWM2.
000 = 1 Time Slot = 35 seconds
001 = 2 Time Slots = 17.6 seconds
010 = 3 Time Slots = 11.8 seconds
011 = 5 Time Slots = 7 seconds
100 = 8 Time Slots = 4.4 seconds
101 = 12 Time Slots = 3 seconds
110 = 24 Time Slots = 1.6 seconds
111 = 48 Time Slots = 0.8 seconds
100
80
PWM DUTY CYCLE (%)
60
40
40
20
0
Another way to view the ramp rates is the time it takes
for the PWM output to ramp from 0% to 100% duty cycle
for an instantaneous change in temperature. This can be
tested by putting the ADT7460/ADT7463 into manual
mode and changing the PWM output from 0% to 100%
PWM duty cycle. The PWM output takes 35 seconds to
reach 100% with a ramp rate of 1 time slot selected.
20
0
4.4
TIME – s
Figure 34 shows the PWM output response for a ramp
rate of 2. In this instance, the fan took about 17.6 seconds to reach full running speed.
120
120
RTEMP (�C)
120
RTEMP (�C)
100
100
100
100
80
80
80
PWM DUTY CYCLE (%)
80
60
60
40
40
60
PWM CYCLE (%)
40
20
0
0
TIME – s
0
0
0.76
Figure 32 shows remote temperature plotted against
PWM duty cycle for enhanced acoustics mode. The
ramp rate is set to 48, which would correspond to the
fastest ramp rate. Assume that a new temperature reading is available every 115 ms. With these settings, it took
approximately 0.76 seconds to go from 33% duty cycle
to 100% duty cycle (full speed). Even though the temperature increased very rapidly, the fan ramps up to full
speed gradually.
Rev. 1 | Page 25 of 27 | www.onsemi.com
REV. 0
TIME – s
17.6
Figure 34. Enhanced Acoustics Mode with
Ramp Rate = 2
Figure 32. Enhanced Acoustics Mode with
Ramp Rate = 48
–25–
60
40
20
20
20
0
0
Figure 33. Enhanced Acoustics Mode with
Ramp Rate = 8
140
140
120
80
60
0
AN-613
Finally, Figure 35 shows how the control loop reacts to
temperature with the slowest ramp rate. The ramp rate
is set to 1, while all other control parameters
remain the same. With the slowest ramp rate selected, it
takes 35 seconds for the fan to reach full speed.
SLOWER RAMP RATES
The ADT7460/ADT7463 can be programmed for much
longer ramp times by slowing the ramp rates. Each
ramp rate can be slowed by a factor of 4.
PWM1 CONFIGURATION REGISTER (Reg. 0x5C)
<3> SLOW = 1 slows the ramp rate for PWM1 by 4.
140
120
RTEMP (�C)
120
100
PWM2 CONFIGURATION REGISTER (Reg. 0x5D)
<3> SLOW = 1 slows the ramp rate for PWM2 by 4.
100
80
80
PWM3 CONFIGURATION REGISTER (Reg. 0x5E)
<3> SLOW = 1 slows the ramp rate for PWM3 by 4.
60
60
PWM DUTY CYCLE (%)
40
The following shows the ramp-up times when the SLOW
bit is set for each PWM output.
40
20
20
0
0
35
TIME – s
ENHANCE ACOUSTICS REGISTER 1 (Reg. 0x62)
<2:0> ACOU Select the ramp rate for PWM1.
000 = 140 seconds
001 = 70.4 seconds
010 = 47.2 seconds
011 = 28 seconds
100 = 17.6 seconds
101 = 12 seconds
110 = 6.4 seconds
111 = 3.2 seconds
0
Figure 35. Enhanced Acoustics Mode with
Ramp Rate = 1
As Figures 32 to 35 show, the rate at which the fan will
react to temperature change is dependent on the ramp
rate selected in the enhance acoustics registers. The
higher the ramp rate, the faster the fan will reach the
newly calculated fan speed.
Figure 36 shows the behavior of the PWM output as temperature varies. As the temperature is rising, the fan
speed ramps up. Small drops in temperature will not
affect the ramp-up function since the newly calculated
fan speed will still be higher than the previous PWM
value. The enhance acoustics mode allows the PWM
output to be made less sensitive to temperature variations. This will be dependent on the ramp rate selected
and programmed into the enhance acoustics registers.
ENHANCE ACOUSTICS REGISTER 2 (Reg. 0x63)
<2:0> ACOU3 Select the ramp rate for PWM3.
000 = 140 seconds
001 = 70.4 seconds
010 = 47.2 seconds
011 = 28 seconds
100 = 17.6 seconds
101 = 12 seconds
110 = 6.4 seconds
111 = 3.2 seconds
90
<6:4> ACOU2 Select the ramp rate for PWM2.
000 = 140 seconds
001 = 70.4 seconds
010 = 47.2 seconds
011 = 28 seconds
100 = 17.6 seconds
101 = 12 seconds
110 = 6.4 seconds
111 = 3.2 seconds
80
70
PWM DUTY CYCLE (%)
60
50
40
RTEMP
30
20
10
0
Figure 36. How Fan Reacts to Temperature Variation in
Enhanced Acoustics Mode
© 2003 Analog Devices, Inc. All rights reserved. Trademarks and registered tradeRev. 1 | Page 26 of 27 | www.onsemi.com
marks are the property of their respective companies.
–26–
REV. 0
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