19-2056; Rev 0; 5/01
Fan Controller/Driver with Factory-
Programmed Temperature Thresholds
General Description
The MAX6665 is a fully integrated thermal switch with
an internal power transistor for driving a cooling fan
rated up to 24V and 250mA. When the MAX6665’s tem-
perature rises above a factory-programmed threshold,
the
FANOUT
pin becomes active and powers the fan.
The MAX6665 is available with factory-programmed fan
activation threshold temperatures from +40°C to +70°C
in 5°C increments. Accuracy of the fan activation trip
point is ±1°C (typ) and ±3°C (max). The trip point’s hys-
teresis is pin selectable to 1°C, 4°C, or 8°C. Two open-
drain logic outputs indicate overtemperature con-
ditions:
WARN
is activated when the temperature is
15°C above the fan activation threshold, and
OT
is acti-
vated when the temperature is 30°C above the thresh-
old. These features can be used to safely power down
systems that are overheated.
The MAX6665 operates from a +2.7V to +5.5V power
supply, and the associated fan can be powered from
4.5V to 24V. It is available in an 8-pin SO package and
operates from -40°C to +125°C.
o
On-Chip 250mA Fan Switch
o
No External Components Required
o
Factory-Programmed Thresholds
o
Two Overtemperature Warning Signals
o
Pin-Selectable 1°C, 4°C, and 8°C Hysteresis
o
Low 65µA Supply Current
Features
MAX6665
Ordering Information
PART
MAX6665ASA40
MAX6665ASA45
MAX6665ASA50
MAX6665ASA55
MAX6665ASA60
MAX6665ASA65
MAX6665ASA70
TEMP.
RANGE
-40°C to
+125°C
-40°C to
+125°C
-40°C to
+125°C
-40°C to
+125°C
-40°C to
+125°C
-40°C to
+125°C
-40°C to
+125°C
PIN-
PACKAGE
8 SO-EP*
8 SO-EP*
8 SO-EP*
8 SO-EP*
8 SO-EP*
8 SO-EP*
8 SO-EP*
THRESHOLD
40°C
45°C
50°C
55°C
60°C
65°C
70°C
Applications
Notebook and Desktop Computers
Servers
PC Power Supplies
Laboratory Instruments
Card Racks
Typical Operating Circuit
+4.5V TO +24V
100mA TO 250mA
COOLING FAN
*Exposed paddle
Pin Configuration
TOP VIEW
+3.3V
1µF
V
DD
FANOUT
V
DD
100kΩ
MAX6665
HYST
WARN
GND
V
DD
100kΩ
1
8
7
FANOUT
V
DD
WARN
OT
FORCEON
2
MAX6665
HYST
3
6
5
FORCEON
GND
OT
FANON
FANON
4
SO
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Fan Controller/Driver with Factory-
Programmed Temperature Thresholds
MAX6665
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND ..............................................................-0.3V to +6V
FANOUT
to GND ....................................................-0.3V to +28V
FORCEON,
HYST, FANON to GND............-0.3V to (V
DD
+ 0.3V)
WARN, OT
to GND ...................................................-0.3V to +6V
FANOUT
Continuous Current............................................400mA
All Other Pins ....................................................................±20mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin SO (derate 19.6mW/°C above +70°C).............1568mW
Operating Temperature Range .........................-40°C to +125°C
Junction (storage) Temperature Range ............-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°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.
ELECTRICAL CHARACTERISTICS
(V
DD
= +2.7V to +5.5V, T
A
= -40°C to +125°C. Typical values are at V
DD
= +3.3V and T
A
= +25°C, unless otherwise noted.) (Note 1)
PARAMETER
Supply Voltage
Supply Current
FANOUT
Drive Voltage
FANOUT
Output Current Capability
FANOUT
Leakage Current
V
DD
pin
No load
FANOUT
pin
V
FANOUT
< 0.8V
V
FANOUT
< 0.6V, T
A
≤
T
TH
+10°C, V
CC
≥
+3.3V
V
FANOUT
= 26V, T
A
= +60°C
MAX6665ASA40
MAX6665ASA45
MAX6665ASA50
FANOUT
Threshold, T
TH
MAX6665ASA55
MAX6665ASA60
MAX6665ASA65
MAX6665ASA70
FANOUT
Threshold Error
HYST is unconnected
FANOUT
Hysteresis
WARN
Threshold
OT
Threshold
WARN
and
OT
Hysteresis
FANON Output High Voltage
FANON Output Low Voltage
WARN
and
OT
Output Voltage Low
Open-Drain Leakage Current
Input Low Voltage
Input High Voltage
Input Current
I
FANON
= 0.5mA source
I
FANON
= 0.5mA sink
I
WARN
= 1.2mA or I
OT
= 1.2mA sink
I
WARN
= 20mA or I
OT
= 20mA sink
V
WARN
= 5.5V or V
OT
= 5.5V
FORCEON
and HYST pins
FORCEON
and HYST pins
FORCEON
connected to V
DD
or GND
HYST connected to V
DD
or GND
0.7V
DD
-1
-15
+1
+15
0.5
0.1
0.3V
DD
2.0
0.7
0.3
HYST
≤
0.3V
DD
HYST
≥
0.7V
DD
Relative to
FANOUT
temperature threshold
Relative to
FANOUT
temperature threshold
-3
250
250
3
40
45
50
55
60
65
70
±1
1
4
8
+15
+30
2
°C
°C
°C
V
V
V
µA
V
V
µA
°C
+3
°C
°C
CONDITIONS
MIN
2.7
65
TYP
MAX
5.5
200
26
UNITS
V
µA
V
mA
µA
Note 1:
Specifications over temperature are guaranteed by design. Parts are 100% production tested at 10°C below the tempera-
ture threshold.
2
_______________________________________________________________________________________
Fan Controller/Driver with Factory-
Programmed Temperature Thresholds
MAX6665
Typical Operating Characteristics
(V
DD
= +3.3V, unless otherwise noted.)
FANOUT VOLTAGE vs. CURRENT
MAX6665 toc01
FANOUT VOLTAGE vs. SUPPLY VOLTAGE
FANOUT CURRENT = 250mA
MAX6665 toc02
900
800
700
FANOUT VOLTAGE (mV)
600
500
400
300
200
100
0
10
T
A
= +75°C
V
DD
= +2.7V
550
500
FANOUT VOLTAGE (mV)
450
400
350
300
250
V
DD
= +3.3V
T
A
= +75°C
T
A
= +50°C
V
DD
= +5.0V
100
FANOUT CURRENT (mA)
1000
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
SUPPLY VOLTAGE (V)
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
MAX6665 toc03
TEMPERATURE THRESHOLD
DISTRIBUTION
MAX6665ASA55
100 SAMPLES
45
PERCENTAGE OF SAMPLES (%)
40
35
30
25
20
15
10
5
MAX6665 toc04
90
80
SUPPLY CURRENT (µA)
70
60
FORCEON = V
DD
50
V
DD
= +5V
V
DD
= +3.3V
V
DD
= +2.7V
50
40
30
-40 -20
0
20
40
60
80 100 120
TEMPERATURE (°C)
0
0
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.5 1.0 1.5 2.0 2.5 3.0
TEMPERATURE ERROR (°C)
_______________________________________________________________________________________
3
Fan Controller/Driver with Factory-
Programmed Temperature Thresholds
MAX6665
Pin Description
PIN
1
2
3
4
5
6
7
8
Exposed
Paddle
NAME
GND
FORCEON
HYST
FANON
OT
WARN
V
DD
FANOUT
GND
Ground
Force Fan On Input. Set
FORCEON
low to force the fan switch on. Set
FORCEON
high for normal
operation.
Three-State Hysteresis Input. Connect HYST to V
DD
for 8°C, GND for 4°C, and leave HYST
unconnected for 1°C hysteresis.
Fan-On Indicator Output. Push-pull output. FANON is high when the fan switch is on. FANON is low
when the fan switch is off.
Overtemperature Output. Active-low when the temperature is 30°C above the fan threshold. Open-
drain output, requires resistive pullup.
Overtemperature Warning Output. Active-low when the temperature is 15°C above the fan
threshold. Open-drain output, requires resistive pullup.
Supply Voltage. Bypass with a 1µF capacitor to GND as close to V
DD
pin as possible.
Fan-Switch (Driver) Output. Connect to the low side of a fan.
Ground
FUNCTION
Detailed Description
The MAX6665 is a simple fan controller/driver that turns
on the internal power transistor when its die tempera-
ture exceeds a factory-set threshold. By connecting a
small (typically 5V to 12V, 100mA to 250mA) cooling
fan to
FANOUT,
a simple on/off fan-control system is
created.
FANOUT
drives the fan’s low side. The fan’s
positive supply pin should be connected to its normal
power-supply voltage (up to 24V nominal).
To turn the fan on when the MAX6665’s die temperature
is less than the threshold voltage, drive
FORCEON
low.
This overrides the internal control circuitry and allows
an external device to activate the fan. FANON is an
active-high push-pull logic output that goes high when
the fan is turned on, either when temperature exceeds
the threshold or the fan is forced on.
WARN
is an active-low, open-drain digital output that
indicates the MAX6665’s die temperature exceeds
15°C above the fan trip threshold.
WARN
output serves
as a warning that the system temperature has contin-
ued to rise well above the fan activation temperature.
OT
is an active-low open-drain digital output that indi-
cates the MAX6665’s die temperature exceeds 30°C
above the fan trip threshold. It serves as a thermal shut-
down output to the system in case of excessive temper-
ature rise. Figure 1 shows a typical application circuit
for a high-reliability, fail-safe temperature monitor.
4
Applications Information
Thermal Considerations and Hysteresis
The temperature comparator has hysteresis to prevent
small temperature changes near the threshold temper-
ature from causing the fan to turn on and off repeatedly
over short periods of time. The
FANOUT
pin goes
active and powers the fan when the MAX6665’s die
temperature exceeds the factory-programmed trip tem-
perature. As the cooling fan operates, the circuit board
temperature should decrease, which in turn causes the
MAX6665’s die temperature to decrease. When the die
temperature is equal to the trip threshold minus the
hysteresis, the
FANOUT
pin turns the fan off, removing
power from the fan. The HYST pin sets the amount of
hysteresis to 1°C, 4°C, or 8°C by letting the pin float or
connecting to GND or V
DD
, respectively. This allows
the amount of hysteresis to be matched to the cooling
and noise requirements of the system.
Hysteresis is also affected by self-heating of the
MAX6665’s die. The fan current flowing through the on-
chip power transistor causes the die temperature to
increase. For example, assume the MAX6665 controls
a 125mA fan. When the fan is operating, the voltage
drop across the output transistor is typically under
250mV. At 250mV, the power dissipation is 31.25mW.
The thermal resistance of the MAX6665 package (with
EP soldered) is 51°C/W, so the die temperature
_______________________________________________________________________________________
Fan Controller/Driver with Factory-
Programmed Temperature Thresholds
MAX6665
+4.5V TO +24V
100mA TO 250mA
COOLING FAN
+3.3V
1µF
V
DD
FANOUT
V
DD
100kΩ
MAX6665
HYST
WARN
I/O
µP
FORCEON
FANON
V
DD
100kΩ
OT
GND
SYSTEM POWER
SHUTDOWN
I/O
Figure 1. High-Reliability, Fail-Safe Fan Controller and Temperature Monitor
increases by a maximum of:
51°C/W x 0.03125W = 1.59°C
Therefore, the effective hysteresis is about 1.59°C high-
er than the hysteresis selected by the HYST pin. For
example, setting the HYST pin for 8°C of hysteresis
results in an effective hysteresis of about 9.6°C.
A larger fan with a power-supply current of 250mA
causes a maximum voltage drop of 0.6V at the output
pin. This results in 150mW power dissipation and the
die temperature increases by:
51°C/W x 0.150W = 7.65°C
If the HYST pin has been set for 8°C of hysteresis, the
total effective hysteresis will be about 15.7°C.
Using fans with somewhat higher operating current
than 250mA results in higher voltage across the output
transistor. The increased power dissipation caused by
the higher current and voltage levels will increase self-
heating, thereby increasing the effective hysteresis.
When using higher-power fans, be sure that the
MAX6665’s power dissipation does not cause so much
self-heating that the MAX6665 stays on constantly.
Locating the MAX6665
The location of the MAX6665 in the system affects its
operation. Because the fan is turned on and off based
on the MAX6665’s die temperature, place the MAX6665
close to major heat-generating components in the sys-
tem—a high-speed CPU or a power device, for exam-
ple. A higher supply voltage reduces the
FANOUT
voltage, which reduces the self-heating effects.
The die temperature of the MAX6665 tracks the tempera-
ture of its leads and the EP. If it is soldered to a PC board,
it quickly reaches the temperature of the traces in that
section of the circuit board. Air temperature affects the die
temperature. Since the plastic package does not conduct
heat as well as the leads, the effect of air temperature is
much less than that of lead temperature.
Layout Issues
The MAX6665’s GND pin is ground return for the fan dri-
ver and the device. Large fan current induces noise
(ground bounce) to the MAX6665. Bypass V
DD
to GND
with a 1µF tantalum capacitor located as close to the
MAX6665 as possible. For long V
DD
and GND lines, an
additional bypass capacitor may be needed. The bypass
capacitor reduces GND noise. The EP is internally con-
nected to the GND pin. Solder the EP to the ground plane
for better electrical and thermal performance.
5
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