MAX31740ATA/VY+ [MAXIM]
Ultra-Simple Fan-Speed Controller;
| 型号： | MAX31740ATA/VY+ |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Ultra-Simple Fan-Speed Controller |
| 文件： | 总11页 (文件大小：628K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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MAX31740
Ultra-Simple Fan-Speed Controller
General Description
Features
The MAX31740 is a sophisticated, yet easy-to-use fan-
speed controller. It monitors the temperature of an external
NTC thermistor and generates a PWM signal that can be
used to control the speed of a 2, 3, or 4-wire fan. The fan
control characteristics are set using external resistors,
thereby eliminating the need for an external microcon-
troller. Controllable characteristics include the starting
temperature for fan control, PWM frequency, fan speed
at low temperatures, and slope of the temperature-duty-
cycle transfer function.
●ꢀ Self-ContainedꢀPWMꢀFanꢀControl—NoꢀMicroꢀNeeded
●ꢀ ControlsꢀSpeedꢀofꢀ2-,ꢀ3-,ꢀorꢀ4-WireꢀFans
●ꢀ ResistorsꢀSetꢀFanꢀControlꢀCharacteristics
●ꢀ Smooth,ꢀLinearlyꢀVaryingꢀPWMꢀDutyꢀCycleꢀMinimizesꢀ
Audibility of Fan Noise
●ꢀ AccuratelyꢀMonitorsꢀExternalꢀThermistorꢀTemperature
●ꢀ 3.0Vꢀtoꢀ5.5VꢀOperatingꢀVoltageꢀRange
●ꢀ -40°Cꢀtoꢀ+125°CꢀOperatingꢀTemperatureꢀRange
●ꢀ AEC-Q100ꢀqualifiedꢀMAX31740ATA/VY+
Because the operating characteristics are selected by
hardwired passive components, a simple, low-cost fan-
speed controller can be implemented without the need
for firmware development. This can dramatically reduce
development time for the fan control function.
Applications
●ꢀ ConsumerꢀEquipment
●ꢀ CommunicationsꢀEquipment
●ꢀ ComputingꢀEquipment
●ꢀ IndustrialꢀEquipment
The MAX31740 is available in a 2mm x 3mm, 8-pin TDFN
package.
Ordering Information appears at end of data sheet.
Typical Application Circuits
2-WIRE FAN-SPEED CONTROLLER
4-WIRE FAN-SPEED CONTROLLER
V
V
V
V
DD
DD
R
ST
C
B
R
ST
C
B
B
B
DD
DD
R
R
VFAN
SENSE
D0
SENSE
D0
R
R
R
R
D1
D1
FREQ
FREQ
C
C
F
F
VFAN
MAX31740
MAX31740
DMIN
DMIN
TACH OR
LOCKED
ROTOR
PWM_OUT
N
PWM_OUT
33Hz
25kHz
D2
D2
GND SLOPE
R
GND SLOPE
R
SLOPE
SLOPE
19-6697; Rev 3; 12/20
MAX31740
Ultra-Simple Fan-Speed Controller
Absolute Maximum Ratings
(All voltages relative to ground.)
StorageꢀTemperatureꢀRange............................ -55°Cꢀtoꢀ+125°C
Junction Temperature Maximum .....................................+150°C
SolderingꢀTemperatureꢀ(reflow).......................................+260°C
VoltageꢀRangeꢀonꢀV
-0.3Vꢀtoꢀ+6.0V
DD..............................................
VoltageꢀRangeꢀonꢀAnyꢀNon-PowerꢀPin .... -0.3Vꢀtoꢀ(V ꢀ+ꢀ0.3V)
DD
OperatingꢀTemperatureꢀRange......................... -40°Cꢀtoꢀ+125°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Package Thermal Characteristics (Note 1)
TDFN
Junction-to-AmbientꢀThermalꢀResistanceꢀ(θ ) ..........60°C/W
JA
Junction-to-CaseꢀThermalꢀResistanceꢀ(θ )...............11°C/W
JC
Note 1:ꢀ PackageꢀthermalꢀresistancesꢀwereꢀobtainedꢀusingꢀtheꢀmethodꢀdescribedꢀinꢀJEDECꢀspecificationꢀJESD51-7,ꢀusingꢀaꢀfour-layerꢀ
board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
Recommended Operating Conditions
(T ꢀ=ꢀ-40°Cꢀtoꢀ+125°C,ꢀunlessꢀotherwiseꢀnoted.)ꢀ(Noteꢀ2)
A
PARAMETER
SupplyꢀVoltage
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
3.0
3.3
5.5
V
V
V
DD
Logicꢀ1ꢀ(D0)
Logicꢀ0ꢀ(D0)
V
V
x 0.7
V
ꢀ+ꢀ0.3
IH
DD
DD
V
-0.3
V
x 0.3
DD
IL
Electrical Characteristics
(V ꢀ=ꢀV
ꢀtoꢀV
, T ꢀ=ꢀ-40°Cꢀtoꢀ+125°C,ꢀunlessꢀotherwiseꢀnoted.)ꢀ(Notesꢀ2,ꢀ3)
DD
DDMIN
DDMAX A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
V
ꢀ=ꢀ3.3V
ꢀ=ꢀ5.5V
ꢀ=ꢀ3.3V
500
750
-40
19
800
1100
+10
DD
DD
DD
SupplyꢀCurrentꢀ(Noteꢀ4)
I
µA
DD
PWMꢀStartꢀVoltageꢀ(Noteꢀ5)
InputꢀBiasꢀCurrentꢀ(SENSE)
InternalꢀDOꢀPulldownꢀResistor
V
-80
20
mV
nA
kΩ
START
I
T =ꢀ+25°Cꢀtoꢀ+125°C
A
BIAS
DO
60
100
RLOAD
InternalꢀSLOPEꢀFeedbackꢀ
Resistanceꢀ(Noteꢀ6)
R
V
ꢀ=ꢀ3.3V,ꢀT =ꢀ+25°C
22 ± 2.4
kΩ
FBK
DD
A
SawtoothꢀPeakꢀVoltageꢀOffsetꢀ
(Note 7)
V
±12
mV
FSOFFSET
SawtoothꢀPeakꢀVoltage
V
0.4925
0.5
0.5075
10
xꢀV
DD
FS
R
ꢀCapacitiveꢀLoadꢀ
SLOPE
C
pF
SLOPE
(Note 8)
PWMꢀOutputꢀLow
PWMꢀOutputꢀHigh
V
I
I
ꢀ=ꢀ6mA
0.4
V
V
OL
SINK
V
ꢀ=ꢀ-6mA
V
- 0.4
OH
SOURCE
DD
10.5455-6/C
Hz
F
PWM Frequency
PWM
T
T
=ꢀ+25°Cꢀtoꢀ+125°C
=ꢀ-40°Cꢀtoꢀ+125°C
-10
-20
+10
+20
FREQ
A
A
%
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MAX31740
Ultra-Simple Fan-Speed Controller
Capacitance
(T ꢀ=ꢀ+25°C,ꢀunlessꢀotherwiseꢀnoted.)
A
PARAMETER
Input Capacitance
OutputꢀCapacitance
Note 2: All voltages referenced to ground.
SYMBOL
CONDITIONS
MIN
TYP
10
MAX
UNITS
pF
C
(Note 9)
(Note 9)
I
C
15
pF
O
Note 3:ꢀ LimitsꢀareꢀproductionꢀtestedꢀatꢀT ꢀ=ꢀ+25°C. Limitsꢀoverꢀtheꢀoperatingꢀtemperatureꢀrangeꢀandꢀrelevantꢀsupplyꢀvoltageꢀrangeꢀ
A
areꢀguaranteedꢀbyꢀdesignꢀandꢀcharacterization.ꢀTypicalꢀvaluesꢀareꢀnotꢀguaranteed.
Note 4:ꢀ SENSEꢀ=ꢀV /2.
DD
Note 5:ꢀ V
ꢀspecifiesꢀtheꢀvoltageꢀchangeꢀrelativeꢀtoꢀV /2ꢀthatꢀisꢀrequiredꢀtoꢀstartꢀPWM.ꢀNegativeꢀvalueꢀindicatesꢀlowerꢀthanꢀ
START
DD
V
/2.
DD
Note 6:ꢀ Theꢀtypicalꢀ(TYP)ꢀcolumnꢀindicatesꢀ±3ꢀsigmaꢀdistributionꢀofꢀaꢀtrimmedꢀresistance.
Note 7:ꢀ V ꢀisꢀspecifiedꢀrelativeꢀtoꢀV /2.ꢀTheꢀtotalꢀerrorꢀequalsꢀV ꢀ+ꢀV
FSOFFSET
.
FSOFFSET
DD
FS
Note 8:ꢀ ForꢀstableꢀPWMꢀoperation,ꢀtheꢀmaximumꢀexternalꢀcapacitanceꢀconnectedꢀtoꢀR
from all sources must be less than
SLOPE
10pF.
Note 9: Guaranteed by design; not 100% production tested.
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MAX31740
Ultra-Simple Fan-Speed Controller
Typical Operating Characteristics
(T ꢀ=ꢀ+25°C,ꢀunlessꢀotherwiseꢀnoted.)
A
PWM_OUT OUTPUT FREQUENCY
POWER-SUPPLY CURRENT
vs. POWER-SUPPLY VOLTAGE
vs. TEMPERATURE
650
600
550
500
450
50
C
= 330nF,
V
C
= 3.3V,
= 330nF,
F
DD
DUTY CYCLE = 50%
F
45
40
35
30
25
20
C = 10pF
L
+125°C
-40°C
3.0
3.5
4.0
4.5
5.0
5.5
6.0
-40
10
20
50
80
110
POWER-SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
THEROETICAL PWM OUTPUT FREQUENCY
vs. FREQ INPUT CAPACITANCE
MEASURED PWM OUTPUT FREQUENCY
vs. FREQ INPUT CAPACITANCE
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
T
A
= +25°C
T = +25°C
A
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
FREQ INPUT CAPACITANCE (F)
FREQ INPUT CAPACITANCE (F)
PWM DUTY CYCLE
PWM_OUT OUTPUT VOLTAGE LOW
vs. OUTPUT CURRENT
PWM_OUT OUTPUT VOLTAGE HIGH
vs. OUTPUT CURRENT
vs. D
INPUT BIAS
MIN
100
80
60
40
20
0
3.30
3.25
3.20
3.15
3.10
3.05
3.00
0.4
0.3
0.2
0.1
0
V
= 3.3V,
= +25°C
DD
V
= 3.3V,
= +25°C
V
= 3.3V,
DD
DD
T
A
T
T = +25°C
A
A
0%
15%
30%
45%
-10
-8
-6
-4
-2
0
0
5
10
15
20
D
BIAS (%V )
DD
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
MIN
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MAX31740
Ultra-Simple Fan-Speed Controller
Pin Configuration
TOP VIEW
DMIN
SLOPE
SENSE
GND
1
2
3
4
8
7
6
5
V
DD
PWM_OUT
D0
MAX31740
TDFN
EP
FREQ
Pin Description
PIN
NAME
FUNCTION
Connect to an external resistor-divider to set the minimum active PWM duty cycle. (Typically between
0.05V ꢀtoꢀ0.2V , depending on desired minimum duty cycle.)
1
DMIN
DD
DD
2
SLOPE
SENSE
Connect to an external resistor to set the slope of the temperature-PWM curve.
ThermistorꢀVoltageꢀInput.ꢀExternalꢀNTCꢀthermistorꢀsensesꢀtemperature.ꢀThermistorꢀandꢀexternalꢀresistorꢀ
formꢀaꢀvoltage-dividerꢀwithꢀaꢀnegativeꢀtemperatureꢀcoefficient.ꢀ
3
4
GND
Ground
5
FREQ
Connect to external capacitor C to set PWM frequency.
F
DutyꢀCycleꢀInput.ꢀSetsꢀtheꢀdutyꢀcycleꢀbelowꢀt
to either D
ꢀorꢀ0%.ꢀConnectꢀtoꢀGNDꢀforꢀ0%ꢀorꢀtoꢀV
MIN
MIN DD
6
D0
for D
.ꢀD0ꢀhasꢀanꢀinternalꢀ60kΩꢀ(typ)ꢀpulldownꢀresistor.
MIN
7
8
PWM_OUT PWMꢀCMOSꢀoutputꢀsignal.ꢀ
V
3.0Vꢀtoꢀ5.5VꢀSupplyꢀVoltageꢀInput.ꢀBypassꢀwithꢀatꢀleastꢀaꢀ0.01µFꢀcapacitor.
DD
ExposedꢀPad.ꢀConnectꢀtoꢀground,ꢀbutꢀdoꢀnotꢀuseꢀasꢀtheꢀsoleꢀgroundꢀconnectionꢀpointꢀorꢀleaveꢀ
unconnected.
—
EP
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MAX31740
Ultra-Simple Fan-Speed Controller
Block Diagram
V
DD
V
FS
V
DD
V
L
FREQ
OSCILLATOR
P
C
F
R
FBK
PWM_OUT
N
SLOPE
R
SLOPE
V
FS
V
DD
∑
R
ST
R
B
SENSE
MAX31740
C
B
60kΩ (TYP)
THERMISTOR
DMIN
D0
V
DD
V
DD
R
D1
R
D2
PWM_OUTꢀ isꢀ aꢀ CMOSꢀ outputꢀ thatꢀ canꢀ beꢀ connectedꢀ
directly to most fans’ speed control input as shown in the
4-WireꢀFan-SpeedꢀControllerꢀgraphꢀinꢀTypical Application
Circuits.
Detailed Description
The MAX31740 monitors the temperature of an external
NTC thermistor and generates a PWM signal that can be
used to control the speed of a 2-, 3-, or 4-wire fan. The fan
control characteristics are set using external resistors and
capacitors, thereby eliminating the need for an external
microcontroller. Controllable characteristics include the
starting temperature for fan control, PWM frequency, fan
speed at low temperatures, and slope of the temperature-
duty-cycle transfer function.
If the fan has no speed control input (this is the case for all
2-wire fans and most 3-wire fans), there are two options
for controlling the fan’s speed. The first option is to use a
low-frequencyꢀ (typicallyꢀ 33Hz)ꢀ PWMꢀ signalꢀ toꢀ modulateꢀ
theꢀfan’sꢀpowerꢀsupplyꢀasꢀshownꢀinꢀtheꢀ2-WireꢀFan-Speedꢀ
Controller graph in Typical Application Circuits.
The advantage of using PWM to modulate the fan’s power
supply is that it is inexpensive. Note, however, that some
fan manufacturers recommend against this approach for
their fans. Before using this approach, be sure to verify
that the fan is compatible with pulse-width modulation
of the power supply. Also, modulating the power-supply
voltage in this manner can cause an increase in the
Controlling Fan Speed
The device generates a PWM signal and varies the duty
cycle of that signal to control the speed of one or more
fans. If the fan has a PWM speed control input (typically
this is a “4-wire” fan), the recommended PWM frequency
isꢀusuallyꢀinꢀtheꢀ20kHzꢀtoꢀ30kHzꢀrange.
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MAX31740
Ultra-Simple Fan-Speed Controller
perceived noise level when the duty cycle is not equal to
100% or 0%.
•
D
is the PWM duty cycle at the lower left end of the
MIN
solid diagonal portion of the curve. It is selected using
a resistor-divider to set the voltage at the DMIN input.
Another option for fans with no speed control input is to
convert the PWM signal to a DC voltage. This can be
done using a simple two-transistor buffer circuit, a linear
low-dropout voltage regulator, or a switch-mode voltage
regulator.ꢀ Alwaysꢀ useꢀ aꢀ highꢀ PWMꢀ frequencyꢀ (20kHzꢀ
or higher recommended) in this case to ease filtering.
Figure 1 shows an example of a two-transistor buffer
circuit.
•
•
T
is the temperature at which the duty cycle begins
MIN
to increase from D
.
MIN
D0 is the value of the PWM duty cycle for tempera-
tures below T . This value is equal to either D
or 0% in curves (b) and (c), depending upon whether
MIN
MIN
D0ꢀisꢀconnectedꢀtoꢀV or GND.
DD
•
The slope of the diagonal portion of the curve is select-
edꢀbyꢀtheꢀvalueꢀofꢀtheꢀresistorꢀatꢀtheꢀSLOPEꢀinput.
Fan Control Profile
Figure 2 shows three general curves of PWM duty cycle
vs. temperature for the device. The important parameters
are listed as follows:
•
T
is the temperature that corresponds to the inter-
START
section of the diagonal portion of the curve, including
the dashed portion in (b) and (c), with 0% duty cycle. It
isꢀselectedꢀbyꢀsettingꢀresistorꢀR
equal to the resis-
ST
tance of the thermistor at temperature T
START.
V
FAN
3.3V
(5V OR 12V)
100kΩ
P
2N3904
MAX31740
100kΩ
33kΩ
PWM_OUT
2.2µF
10µF
9.1kΩ
Figure 1. Two-Transistor Buffer
a) D
= 0%, D0 = GND
b) D
> 0%, D0 = GND
c) D > 0%, D0 = V
MIN DD
MIN
MIN
100
100
100
D
MIN
D
MIN
D
MIN
T
TEMPERATURE (°C)
T
T
TEMPERATURE (°C)
T T
START MIN
TEMPERATURE (°C)
START
START MIN
Figure 2. PWM Duty Cycle vs. Temperature
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MAX31740
Ultra-Simple Fan-Speed Controller
D
MIN
and D0
Operation
As seen in the Block Diagram, C sets the frequency of
SelectꢀD
and D0 based on the system requirements
F
MIN
the internal saw-tooth oscillator that is used to generate
the PWM speed control signal. The oscillator’s output
and the type of fan to be used. For example, in some
systems, the optimum cooling strategy requires that
the fan stop spinning when the temperature is below a
voltageꢀswingsꢀfromꢀnear-zeroꢀtoꢀV ꢀ(V /2).
FS DD
specific value (T
with the fan profile shown in Figure 2(c).ꢀTheꢀvoltageꢀV
at the DMIN input selects the minimum duty cycle using
the following equation:
).ꢀSuchꢀaꢀschemeꢀcanꢀbeꢀachievedꢀ
MIN
Theꢀ externalꢀ NTCꢀ thermistorꢀ andꢀ resistorꢀ (R ) form a
voltage-divider whose output voltage is approximately
linear and has a negative temperature coefficient. This
ST
MIN
voltageꢀisꢀsubtractedꢀfromꢀV
to create a voltage with
FS
a positive temperature coefficient at the input to the
amplifier. The amplifier’s closed-loop gain is set by an
V
/V ꢀ=ꢀR2/(R1+R2)ꢀ=ꢀD
(%)/200
MIN DD
MIN
where D
is the minimum duty cycle (in percent).
MIN
externalꢀresistorꢀ(R
)ꢀandꢀanꢀinternalꢀ25kΩꢀresistorꢀ
SLOPE
(R
).ꢀTheꢀ valueꢀ ofꢀ R
therefore determines the
For example, if a minimum duty cycle of 30% is desired,
theꢀvoltageꢀatꢀtheꢀDMINꢀinputꢀshouldꢀbeꢀ15%ꢀofꢀV
FBK
SLOPE
slope of the duty cycle as a function of temperature. The
temperature at which the thermistor’s resistance is equal
toꢀR is the nominal value of T
.
DD
When the temperature drops below T
in the profile
MIN
.
ST
START
shown in Figure 2(b),ꢀtheꢀdutyꢀcycleꢀshouldꢀdropꢀtoꢀzero.ꢀ
The voltage at D
, derived by the voltage-divider
MIN
This is accomplished by connecting the D0 input to GND.
betweenꢀ V
and GND, determines the minimum duty
DD
If the system requires a profile like the one in Figure
cycle. The logic level at D0 determines whether the low-
temperature duty cycle will be 0% or equal to D
2(c), where the duty cycle remains at D
when the
MIN
.
MIN
temperature drops below T
,ꢀsimplyꢀconnectꢀD0ꢀtoꢀV
.
MIN
DD
Someꢀfansꢀwithꢀspeedꢀcontrolꢀinputsꢀ(theseꢀareꢀtypicallyꢀ
4-wire fans) are designed to keep spinning at a reduced
speedꢀ evenꢀ whenꢀ theꢀ dutyꢀ cycleꢀ isꢀ equalꢀ toꢀ zero.ꢀ Forꢀ
such fans, a profile like that of Figure 2(a) is usually
appropriate. With this profile, the duty cycle decreases
linearlyꢀtoꢀzeroꢀasꢀtemperatureꢀdecreases.ꢀToꢀachieveꢀthisꢀ
profile, connect D0 to GND.
Component Selection
Before picking component values, be sure that you have
determined target values for the important parameters
such as PWM frequency, T
, D
, D0, and the
MIN
START
slope of the duty cycle vs. temperature curve. Most of
these parameters are defined in the Fan Control Profile
section.
Thermistor
PWM Frequency
Useꢀ aꢀ standardꢀ NTCꢀ thermistor.ꢀAꢀ +25°Cꢀ resistanceꢀ inꢀ
theꢀ10kΩꢀtoꢀ50kΩꢀrangeꢀworksꢀwell.ꢀAnꢀNTC’sꢀresistance-
temperature curve is generally very nonlinear, but when
If the fan has a speed control input, the most common
recommendedꢀPWMꢀfrequencyꢀisꢀ25kHz,ꢀalthoughꢀsomeꢀ
fans require different frequencies. If the fan has no PWM
input and will be controlled by applying the PWM signal
directly to a power-supply modulation transistor (as in
the typical 2-wire fan-speed controller circuit), the PWM
frequencyꢀshouldꢀnormallyꢀbeꢀinꢀtheꢀ25Hzꢀtoꢀ35Hzꢀrange.ꢀ
Aꢀgoodꢀstartingꢀpointꢀisꢀ33Hz.
combinedꢀ withꢀ R
in a voltage-divider, the resulting
ST
curve is reasonably linear over the temperature range of
interest.
R
ST
First determine T
. In Figure 2(a), T
is the
START
START
C sets the PWM frequency according to the equation:
F
temperature at which the duty-cycle curve intersects the
C ꢀ=ꢀ10.5455E-6/FREQꢀ(Hz)
horizontalꢀ axis.ꢀ Inꢀ Figure 2(b) and Figure 2(c), T
can be determined by continuing the diagonal line until
itꢀ crossesꢀ theꢀ horizontalꢀ axis,ꢀ andꢀ theꢀ pointꢀ atꢀ whichꢀ itꢀ
START
F
The most common values of C are 330nF for f
=
PWM
F
33Hzꢀandꢀ430pFꢀforꢀf ꢀ=ꢀ25kHz.
PWM
intersectsꢀtheꢀhorizontalꢀaxisꢀisꢀT
.ꢀNowꢀchooseꢀR
START
ST
equal to the resistance of the thermistor at T
.
START
T
START
SelectꢀR equal to the resistance of the thermistor at the
ST
desired value of T
.
START
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MAX31740
Ultra-Simple Fan-Speed Controller
Slope
R
ST
and R
Example Values
SLOPE
R
sets the slope of the duty cycle vs. temperature
Table 1ꢀ givesꢀ exampleꢀ valuesꢀ ofꢀ R ꢀ andꢀ R
for
SLOPE
SLOPE
ST
curve.Pickthevaluebasedonthethermistorcharacteristics
three values of T
and three fan control temperature
START
and the desired range of temperatures between T
the point where the duty cycle reaches 100%.
and
spans.ꢀ Valuesꢀ areꢀ givenꢀ forꢀ twoꢀ standardꢀ thermistorꢀ
products,ꢀoneꢀratedꢀatꢀ10kΩꢀandꢀtheꢀotherꢀratedꢀatꢀ15kΩꢀ
atꢀ+25°C.
MIN
Asꢀanꢀexample,ꢀassumeꢀthatꢀaꢀtypicalꢀNTCꢀthermistorꢀ+ꢀ
ꢀcombinationꢀwillꢀprovideꢀaꢀslopeꢀofꢀaboutꢀ1%ꢀofꢀV
R
ST
DD
FS
C and R
B
B
perꢀ°C.ꢀSinceꢀV ꢀ=ꢀV /2,ꢀthisꢀisꢀequivalentꢀtoꢀ2%ꢀofꢀV
FS
DD
Oneꢀ ofꢀ theꢀ mostꢀ commonꢀ reasonsꢀ forꢀ controllingꢀ fanꢀ
speed is to reduce the audible noise perceived by users
in the vicinity of the equipment. The audibility of fan noise
increases significantly when the fan speed undergoes
rapid changes. When the thermistor is in contact with a
significant mass, such as a heat sink or a printed circuit
board, the thermal mass of the object being measured will
oftenꢀlimitꢀtheꢀrateꢀofꢀchangeꢀofꢀtheꢀvoltageꢀatꢀtheꢀSENSEꢀ
input so that any fan speed changes are slow and no
additionalꢀfilteringꢀisꢀneeded.ꢀInꢀsuchꢀcases,ꢀRBꢀandꢀCBꢀ
are not necessary.
perꢀ°Cꢀatꢀtheꢀinputꢀtoꢀtheꢀinternalꢀamplifier.ꢀTherefore,ꢀtheꢀ
range of duty cycles from 0% to 100% would correspond
toꢀaboutꢀaꢀ50°Cꢀrangeꢀofꢀtemperaturesꢀwhenꢀtheꢀamplifierꢀ
gain is equal to one. In most implementations, you would
wantꢀaꢀsmallerꢀtemperatureꢀrangeꢀ(forꢀexample,ꢀ15°C)ꢀtoꢀ
cause the duty cycle to cover the full 0% to 100% range.
Doing so requires an amplifier gain of:
A
Vꢀ
=ꢀ50°C/15°Cꢀ=ꢀ3.33
The closed-loop gain of the internal amplifier is:
A ꢀ=ꢀ(1ꢀ+ꢀR /R ).
V
FBK SLOPE
In some cases, the thermistor could be in contact with
an object whose temperature changes relatively rapidly,
or a low-mass thermistor can be suspended in an area
where air flow could cause its temperature to undergo
Therefore:
ꢀ=ꢀR
R
/(A ꢀ–ꢀ1)ꢀ=ꢀ25kΩ/(3.33ꢀ–ꢀ1)ꢀ=ꢀ10.7kΩ
FBK V
SLOPE
Table 1. R and R
Resistor Options
ST
SLOPE
R
(kΩ)
CONTROL RANGE
(T to T ) (°C)
R
SLOPE
(kΩ)
ST
THERMISTOR
T
START
START
100%
+10
+15
+20
+10
+15
+20
+10
+15
+20
+10
+15
+20
+10
+15
+20
+10
+15
+20
6.65
11
25
10
16.2
6.49
10.5
15.4
6.04
10
BetaTHERMꢀ10K3A1
30
35
25
30
35
8.06
6.49
15
14.7
5.49
8.87
13
5.23
8.45
12.4
5.36
8.45
12.4
MurataꢀNCP15XW153J03RC
12.4
10.5
Maxim Integrated
│ 9
www.maximintegrated.com
MAX31740
Ultra-Simple Fan-Speed Controller
fast changes. In these cases, the temperature changes
can be fast enough to cause audible fan speed variations.
Toꢀminimizeꢀthisꢀeffect,ꢀtheꢀrateꢀatꢀwhichꢀtheꢀdutyꢀcycleꢀ
canꢀchangeꢀcanꢀbeꢀslowedꢀdownꢀusingꢀanꢀexternalꢀRCꢀ
Applications Information
Power-Supply Decoupling
To achieve the best results when using the device,
networkꢀconsistingꢀofꢀR and C and connected to the
decoupleꢀtheꢀV
power supply with a (minimum) 0.01µF
B
B
DD
SENSEꢀ input.ꢀTypicalꢀ valuesꢀ forꢀ theseꢀ componentsꢀ areꢀ
5MΩꢀ andꢀ 1µF,ꢀ althoughꢀ theyꢀ canꢀ beꢀ easilyꢀ adjustedꢀ toꢀ
conform to the requirements of the system.
capacitor.ꢀ Useꢀ aꢀ high-quality,ꢀ ceramic,ꢀ surface-mountꢀ
capacitorꢀ ifꢀ possible.ꢀ Surface-mountꢀ componentsꢀ mini-
mizeꢀleadꢀinductance,ꢀwhichꢀimprovesꢀperformance,ꢀandꢀ
ceramic capacitors tend to have adequate high-frequency
response for decoupling applications.
C ꢀcanꢀbeꢀconnectedꢀtoꢀGND,ꢀV , or an intermediate
B
DD
voltage depending on the desired startup characteristics.
Whenꢀ connectedꢀ toꢀ V , C ꢀ initiallyꢀ holdsꢀ theꢀ SENSEꢀ
DD
B
Handling, PCB Layout, and Assembly
inputꢀ highꢀ uponꢀ applicationꢀ ofꢀ V , which delays the
DD
Theꢀ lead-free/RoHSꢀ packageꢀ canꢀ beꢀ solderedꢀ usingꢀ aꢀ
reflowꢀprofileꢀthatꢀcompliesꢀwithꢀJEDECꢀJ-STD-020.
onset of the PWM signal when D0 is grounded and
theꢀ temperatureꢀ onꢀ applicationꢀ ofꢀ V
is greater than
DD
T
. The delay time is related to the time constant
Moisture-sensitive packages are shipped from the factory
dry-packed.ꢀHandlingꢀinstructionsꢀlistedꢀonꢀtheꢀpackageꢀ
label must be followed to prevent damage during reflow.
Referꢀ toꢀ theꢀ IPC/JEDECꢀ J-STD-020ꢀ standardꢀ forꢀ mois-
ture-sensitiveꢀdeviceꢀ(MSD)ꢀclassifications.
START
C R . When connected to GND, C briefly keeps the
SENSEꢀ inputꢀ lowꢀ uponꢀ applicationꢀ ofꢀ V , providing a
“spin-up” function on power-up that can be useful in some
cases (but is generally not necessary). Connecting C to
B
B
B
DD
B
aꢀvoltage-dividerꢀthatꢀproducesꢀanꢀoutputꢀofꢀV /2ꢀcanꢀbeꢀ
DD
usedꢀtoꢀminimizeꢀanyꢀspin-upꢀorꢀdelayꢀtime.
Ordering Information
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
thatꢀaꢀ“+”,ꢀ“#”,ꢀorꢀ“-”ꢀinꢀtheꢀpackageꢀcodeꢀindicatesꢀRoHSꢀstatusꢀ
only. Package drawings may show a different suffix character, but
theꢀdrawingꢀpertainsꢀtoꢀtheꢀpackageꢀregardlessꢀofꢀRoHSꢀstatus.
PART NUMBER
MAX31740ATA+
TEMP RANGE
PIN-PACKAGE
-40°Cꢀtoꢀ+125°C
8ꢀTDFN-EP*
MAX31740ATA/VY+
-40°Cꢀtoꢀ+125°C 8ꢀTDFNꢀ(SWꢀEP*)
+ꢀDenotes a lead(Pb)-free/RoHS-compliant package.
/V = Denotes automotive grade.
Y = Denotes side-wettable.
SW = Denotes side-wettable package.
* EP = Exposed pad.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
8ꢀTDFN-EP
T823+1
21-0174
90-0091
90-0091
8ꢀTDFNꢀ(SWꢀEP)
T823Y+3
21-100417
Chip Information
SUBSTRATEꢀCONNECTEDꢀTOꢀGROUND
PROCESS:ꢀCMOS
Maxim Integrated
│ 10
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MAX31740
Ultra-Simple Fan-Speed Controller
Revision History
REVISION REVISION
PAGES
CHANGED
DESCRIPTION
NUMBER
DATE
0
1
2
3
5/13
Initial release
—
4
7/19
UpdatedꢀTOC06
3/20
UpdatedꢀOrderingꢀInformationꢀtableꢀandꢀPackageꢀInformationꢀtable
UpdatedꢀFeatures section
10
1
12/20
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
©
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
2020 Maxim Integrated Products, Inc.
│ 11
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