19-2133; Rev 2; 11/02
Remote Temperature Switches with Integrated
Fan Controller/Driver
General Description
The MAX6668/MAX6670 remote-junction thermal
switches with an internal power transistor drive a cool-
ing fan rated for supply voltages up to +12V and
250mA. These devices measure the temperature of an
external P-N junction (typically a diode-connected tran-
sistor) and turn on the fan power switch when the
remote temperature rises above a factory-programmed
threshold. Self-contained and requiring no software
development, the MAX6668/MAX6670 are simple
“drop-in” fan-control solutions for a variety of systems.
The MAX6670 features an open-drain
WARN
output
that goes active when the remote temperature exceeds
the factory-programmed fan activation threshold by
+15°C. The MAX6670 features an open-drain
OT
output
that goes active when the remote temperature exceeds
the factory-programmed threshold by +30°C. The
MAX6668/MAX6670 provide a fan-control input,
FORCEON,
that allows the fan to be driven externally,
regardless of temperature.
Available temperature thresholds range from +40°C to
+75°C in 5°C increments. Hysteresis is preset to 8°C on
the MAX6668 or pin selectable to 4°C, 8°C, or 12°C
using a three-level logic input on the MAX6670.
Temperature threshold accuracy is ±1°C (typ) and
±2.2°C (max) for remote-junction temperatures from
+40°C to +75°C.
The MAX6668/MAX6670 operate from a +3V to +3.6V
power supply, and are specified over the automotive
temperature range (-40°C to +125°C). The MAX6668 is
offered in an 8-pin µMAX package and the MAX6670 is
available in a space-saving 10-pin µMAX package.
o
+12V, 250mA Integrated Fan Driver
o
No Calibration Required
o
Pin-Selectable 4°C, 8°C, or 12°C Hysteresis
(MAX6670)
o
Factory-Programmed Temperature Thresholds
from +40°C to +75°C
o
Overtemperature Warning Signals
o
110µA (typ) Supply Current
o
Space-Saving 8-Pin and 10-Pin µMAX Packages
Features
MAX6668/MAX6670
Ordering Information
PART
TEMP
RANGE
PI N-
PA CK AG E
8 µMAX
8 µMAX
8 µMAX
8 µMAX
8 µMAX
8 µMAX
THRESH-
OLD
(
°
C)
40
45
50
60
70
75
MAX6668AUA40
-40°C to +125°C
MAX6668AUA45 -40°C to +125°C
MAX6668AUA50 -40°C to +125°C
MAX6668AUA60 -40°C to +125°C
MAX6668AUA70 -40°C to +125°C
MAX6668AUA75 -40°C to +125°C
Ordering Information continued at end of data sheet.
Typical Application Circuit
+12V
250mA
FAN
FANOUT
V
DD
10kΩ
Applications
Notebook and Desktop Computers
Network Switches
PC Power Supplies
Laboratory Instruments
Card Racks
Temperature Alarms
Fan Controls
2N3904
C
S
2200pF
DXN
DXP
+3.3V
V
DD
MAX6670
WARN
V
DD
10kΩ
HYST
GND
OT
PGND
FORCEON
V
DD
Pin Configuration appears at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
________________________________________________________________
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.
Remote Temperature Switches with Integrated
Fan Controller/Driver
MAX6668/MAX6670
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND ..............................................................-0.3V to +6V
PGND to GND .......................................................-0.3V to +0.3V
FANOUT
to GND ....................................................-0.3V to +15V
DXN to GND ..........................................................-0.3V to +0.8V
DXP,
WARN,
HYST,
FORCEON, OT...........-0.3V
to (V
DD
+ 0.3V)
Current into V
DD
, GND, DXP, DXN,
WARN,
HYST,
FORCEON, OT..............................................................±20mA
Current into
FANOUT,
PGND ........................................ ±300mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin µMAX (derate 4.1mW/°C above +70°C) .............333mW
10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range .............................-60°C to +150°C
Junction Temperature ......................................................+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
= +3V to +3.6V, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at V
DD
= +3.3V and T
A
= +25°C.)
PARAMETER
POWER SUPPLY
Power-Supply Range
Average Supply Current
Operating Current
Power-On Reset (POR) Threshold
POR Threshold Hysteresis
TEMPERATURE SENSOR
FANOUT
Temperature
Threshold Accuracy
T
RJ
= +40°C to +75°C (Note 1),
T
A
= 0°C to +85°C, V
DD
= +3.3V
T
RJ
= +40°C to +75°C (Note 1),
T
A
= -40°C to +125°C, V
DD
= +3.3V
HYST = GND
FANOUT
Temperature
Threshold Hysteresis
WARN
Temperature Threshold
(MAX6670 Only)
OT
Temperature Threshold
(MAX6670 Only)
Supply Sensitivity of Temperature
Threshold
Temperature Sample Frequency
FAN DRIVE OUTPUT
FANOUT
Output Voltage Low
Thermal Shutdown
Thermal Shutdown Hysteresis
LOGIC INPUT/OUTPUT
FORCEON
Input High Voltage
V
IH
0.8 x
V
DD
V
V
OL
I
SINK
= 250mA
0.5
170
20
1
V
°C
°C
3.3
T
HYST
MAX6670
MAX6668
Relative to
FANOUT
temperature threshold
Relative to
FANOUT
temperature threshold
HYST = float
HYST = V
DD
±1
±1
4
8
12
8
+15
+30
1
4
1.6
°C
°C
°C/V
Hz
°C
±2.2
°C
±4
POR
V
DD
I
DD
During sampling
V
DD
falling edge
1
3
110
400
1.5
50
3.6
200
650
2.0
V
µA
µA
V
mV
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
∆T
TH
2
_______________________________________________________________________________________
Remote Temperature Switches with Integrated
Fan Controller/Driver
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +3V to +3.6V, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at V
DD
= +3.3V and T
A
= +25°C.)
PARAMETER
FORCEON
Input Low Voltage
FORCEON
Input Bias Current
WARN, OT
Output Voltage Low
WARN, OT
Output High Leakage
Current
V
OL
I
OH
SYMBOL
V
IL
V
FORCEON
= V
DD
or GND
I
SINK
= 6mA
V
WARN
or V
OT
= +5.5V
CONDITIONS
MIN
TYP
MAX
0.2 x
V
DD
1
0.5
1
UNITS
V
µA
V
µA
MAX6668/MAX6670
Note 1:
T
RJ
is the temperature of the remote P-N junction.
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
FANOUT CURRENT
vs. FANOUT VOLTAGE
MAX6668/70 toc01
FANOUT VOLTAGE
vs. SUPPLY VOLTAGE
MAX6668/70 toc02
SUPPLY CURRENT
vs. TEMPERATURE
V
DD
= +3.3V, I
FANOUT
= 250mA
120
100
MAX6668/70 toc03
0.7
T
A
= +25°C
0.6
0.5
V
FANOUT
(V)
0.4
0.3
0.2
0.1
0
0
50
100
150
200
250
V
DD
= +3.3V
2.0
1.8
1.6
1.4
V
FANOUT
(V)
T
A
= +105°C
T
A
= +65°C
I
FANOUT
= 250mA
140
I
DD
(µA)
1.2
1.0
0.8
0.6
0.4
0.2
0
80
60
40
T
A
= +25°C
2.0
2.5
3.0
V
DD
(V)
3.5
20
0
0
25
50
75
TEMPERATURE (°C)
100
300
I
FANOUT
(mA)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6668/70 toc04
TEMPERATURE THRESHOLD ERROR
MAX6670AUB040
119 SAMPLES
MAX6668/70 toc05
140
120
100
I
DD
(µA)
80
60
40
20
FORCEON = V
DD
0
3.0
3.3
V
DD
(V)
30
PERCENTAGE OF SAMPLES (%)
25
20
15
10
5
3.6
0
-1.00 -0.75 -0.50 -0.25
0
0.25 0.50 0.75
1.00
THRESHOLD ERROR (°C)
_______________________________________________________________________________________
3
Remote Temperature Switches with Integrated
Fan Controller/Driver
MAX6668/MAX6670
Pin Description
PIN
MAX6668
1
2
MAX6670
1
5
PGND
FORCEON
Power Ground. PGND is the power ground for the
FANOUT
power MOSFET switch.
Fan-Control Input. Drive
FORCEON
high for normal operation. Drive
FORCEON
low
to force fan on.
Current Source Positive Input. Connect to the anode of the external diode-
connected transistor. Do not leave DXP floating. Connect a 2200pF capacitor
between DXP and DXN for noise filtering.
Current Sink Negative Input. Connect to the cathode of the external diode-
connected transistor. DXN is internally biased to a diode voltage drop.
Ground
Positive Power Supply
Fan-Drive Output.
FANOUT
is an open-drain power MOSFET that sinks up to 250mA
current to turn on the fan when the sensed temperature exceeds the fan trip
threshold or the fan is forced on by driving
FORCEON
low.
Temperature Warning Output.
WARN
is an open-drain output that goes low when
the sensed junction temperature is 15°C higher than the fan trip threshold.
Overtemperature Output.
OT
is an open-drain output that goes low when the sensed
junction temperature is 30°C higher than the fan trip threshold.
Hysteresis Control Input. HYST is a three-level logic input for controlling the fan-
drive comparator’s hysteresis. Connect HYST to GND for 4°C hysteresis, to V
DD
for
12°C hysteresis, or leave floating for 8°C hysteresis.
NAME
FUNCTION
3
3
DXP
4
5, 7
6
8
4
7
8
10
DXN
GND
V
DD
FANOUT
—
—
2
6
WARN
OT
—
9
HYST
Detailed Description
The MAX6668/MAX6670 are simple fan controllers/dri-
vers that turn on an internal power transistor when the
sensed temperature of an external P-N junction
exceeds a factory-set threshold. By connecting a small
(up to +12V/250mA nominal) cooling fan to
FANOUT,
a
simple on/off fan-control system is created. Do not con-
nect the fan to a power supply of higher than 12V nomi-
nal, 15V maximum.
Overtemperature Alarm Outputs
WARN Output (MAX6670 Only)
WARN
is an active-low, open-drain digital output that
indicates when the external P-N junction’s temperature
exceeds 15°C above the fan trip threshold. The
WARN
output serves as a warning that the system temperature
has continued to rise well above the fan activation tem-
perature.
OT Output (MAX6670 Only)
OT
is an active-low, open-drain digital output that indi-
cates when the external P-N junction’s temperature
exceeds 30°C above the fan trip threshold.
OT
serves
as a thermal shutdown output to the system in case of
excessive temperature rise.
FANOUT
Driver and
FORCEON
Controller
FANOUT Fan-Driver Output
FANOUT
is an open-drain output that sinks greater than
250mA of current to turn on the fan, either when the fan
trip threshold is exceeded or the fan is forced on by dri-
ving
FORCEON
low.
FORCEON Fan-Control Input
Drive
FORCEON
low to turn on the fan when the
MAX6670’s remote-sensing junction temperature is less
than the fan trip threshold temperature. This overrides
the internal control circuitry and allows for an external
device to activate the fan.
4
Hysteresis Input
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 external P-N junc-
tion’s temperature exceeds the factory-programmed
_______________________________________________________________________________________
Remote Temperature Switches with Integrated
Fan Controller/Driver
trip temperature. As the cooling fan operates, the cir-
cuit board temperature should decrease, which causes
the external P-N junction’s temperature to decrease.
When the P-N junction’s temperature is equal to the trip
threshold minus the hysteresis, the
FANOUT
pin turns
the fan off, removing power from the fan. For the
MAX6670, HYST is a three-level logic input for control-
ling the fan-drive comparator’s hysteresis. Connect
HYST to GND to select 4°C hysteresis, to V
DD
to select
12°C hysteresis, or leave floating to select 8°C hystere-
sis. The MAX6668 has a built-in hysteresis of 8°C. This
allows the amount of hysteresis to be matched to the
cooling and noise requirements of the system. Figure 1
shows the temperature trip threshold hysteresis.
MAX6668/MAX6670
Table 1. Remote-Sensor Transistor
Manufacturers
MANUFACTURER
Central Semiconductor (USA)
ON Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
Siemens (Germany)
Zetex (England)
MODEL NO.
CMPT3904
2N3904, 2N3906
SST3904
KST3904-TF
SMBT3904
FMMT3904CT-ND
Applications Information
Remote-Diode Selection
The MAX6668/MAX6670 directly measure the die tem-
perature of CPUs and other ICs that have on-board tem-
perature-sensing diodes (see
Typical Operating Circuit)
or they can measure the temperature of a discrete
diode-connected transistor. For best accuracy, the dis-
crete transistor should be a small-signal device with its
collector and base connected together. Several satisfac-
tory discrete sensing transistors are shown in Table 1.
The sensing transistor must be a small-signal type with
a relatively high forward voltage. Otherwise, the DXP
input voltage range may be violated. The forward volt-
age at the highest expected temperature must be
greater than 0.25V at 10µA, and at the lowest expected
temperature, forward voltage must be less than 0.95V
at 100µA. Do not use large power transistors. Also,
ensure that the base resistance is less than 100Ω. Tight
specifications for forward current gain (50 < B
F
< 150,
for example) indicate that the manufacturer has good
process controls and that the transistors have consis-
tent V
BE
characteristics.
Noise-Filtering Capacitor
In noisy environments, high-frequency noise can be
attenuated using an external 2200pF capacitor located
at the DXP and DXN pins. Larger capacitor values may
be used for additional filtering, but do not exceed
3300pF; excessive capacitance increases error. Figure
2 shows the recommended DXP/DXN PC traces.
Bypassing and Layout
The location of the remote-sensing junction in the sys-
tem affects the MAX6668/MAX6670s’ operation. When
using a discrete temperature-sensing transistor, place
the sensing junction close to major heat-generating
components, such as a high-speed CPU or a power
device.
To minimize noise and other errors, follow the guide-
lines below:
1) Place the MAX6668/MAX6670 as close as possible to
the remote diode. In a noisy environment, such as a
computer motherboard, this distance can be 10cm to
20cm (typ) or more as long as the worst noise
sources (such as CRTs, clock generators, memory
buses, and ISA/PCI buses) are avoided. In general,
minimize the distance to the remote-sensing junction.
2) Do not route the DXP/DXN traces next to the deflec-
tion coils of a CRT. Also, do not route the traces
across a fast memory bus, which can introduce
+30°C error or more, even with good filtering.
3) Route the DXP and DXN traces in parallel and in
close proximity to each other, away from any high-
voltage traces, such as +12VDC. Avoid leakage cur-
rents from PC board contamination, since a 20MΩ
leakage path from DXP to GND causes about +1°C
error.
4) Connect guard traces to GND on either side of the
DXP/DXN traces (Figure 2). With guard traces in
place, routing near high-voltage traces is no longer
an issue.
5) Route through as few vias and crossunders as possi-
ble to minimize copper/solder thermocouple effects.
6) Use wide traces where possible. Narrow traces are
more inductive and tend to pick up radiated noise.
7) Do not use copper as an EMI shield. Only ferrous
materials such as steel work well. Placing a copper
ground plane between the DXP/DXN traces and
other traces carrying high-frequency noise signals
does not help reduce EMI.
The MAX6668/MAX6670s’ PGND is the ground return
for the fan driver. Bypass V
DD
to GND with a 1µF
capacitor located as close to V
DD
as possible. Add
additional bypass capacitors for long V
DD
and GND
lines.
_______________________________________________________________________________________
5
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