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19-2459; Rev 2; 4/03
Dual-Output Remote-Junction
Temperature Switches
General Description
MAX6685/MAX6686 are dual-output temperature switches
that use an external diode-connected transistor as a sens-
ing element. These devices have two logic outputs (T
HIGH
and T
LOW
). T
HIGH
asserts a logic signal when the remote
temperature crosses the factory-programmed, +120°C, or
+125°C upper trip threshold. T
LOW
is asserted when the
remote temperature exceeds the lower threshold, which is
controlled by pins S1 and S2. The lower thresholds are
available in two ranges in 5°C increments. The two ranges
are +40°C to +80°C and +75°C to +115°C. Hysteresis for
both outputs to be deasserted is typically 5°C.
T
HIGH
is an open-drain, active-low output for both the
MAX6685 and the MAX6686. T
LOW
is a CMOS push-pull,
active-high output for the MAX6685 and is an open-drain,
active-low output for the MAX6686. They are available in
a space-saving 8-pin µMAX package.
Features
o
Pin-Programmed Lower Temperature Threshold
from +40°C to +80°C or +75°C to +115°C
(5°C Increments)
o
Preset Upper Threshold: +120°C or +125°C
o
Open-Drain, Active-Low Output for Upper
Temperature Alarm
o
CMOS Push-Pull, Active-High or Open-Drain,
Active-Low Output for Lower Temperature Alarm
o
1.5°C Accuracy
o
3.0V to 5.5V, 200µA Supply
o
8-Pin µMAX Package
MAX6685/MAX6686
Applications
CPU Temperature
Protection
Fan Control
Multichip Modules
FPGA Temperature
Protection
Pin Configurations appear at end of data sheet.
Ordering Information
PART
MAX6685AU40L
MAX6685AU40H
MAX6685AU75L
MAX6685AU75H
MAX6686AU40L
MAX6686AU40H
MAX6686AU75L
MAX6686AU75H
T
LOW
OUTPUT
Push-pull, active high
Push-pull, active high
Push-pull, active high
Push-pull, active high
Open drain, active low
Open drain, active low
Open drain, active low
Open drain, active low
T
LOW
TRIP
RANGE (0°C)
+40°C to +80°C
+40°C to +80°C
+75°C to +115°C
+75°C to +115°C
+40°C to +80°C
+40°C to +80°C
+75°C to +115°C
+75°C to +115°C
T
HIGH
TRIP
THRESHOLD (0°C)
+120°C
+125°C
+120°C
+125°C
+120°C
+125°C
+120°C
+125°C
PIN-PACKAGE
8 µMAX
8 µMAX
8 µMAX
8 µMAX
8 µMAX
8 µMAX
8 µMAX
8 µMAX
Typical Operating Circuits
3.3V
V
DD
TO SYSTEM
SHUTDOWN
T
HIGH
12V
CPU
C
S
DXN
S1
T
LOW
GND
N
S2
GND
T
LOW
DXP
3.3V
V
DD
CPU
C
S
DXP
T
HIGH
TO SYSTEM
SHUTDOWN
MAX6685
DXN
S1
S2
MAX6686
TO CLOCK
THROTTLE
CONTROL
________________________________________________________________
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.
Dual-Output Remote-Junction
Temperature Switches
MAX6685/MAX6686
ABSOLUTE MAXIMUM RATINGS
Voltages Referenced to GND
V
DD,
T
LOW
, T
HIGH
.....................................................-0.3V to +6V
DXN .......................................................................-0.3V to +0.8V
All Other Pins..............................................-0.3V to (V
DD
+ 0.3V)
Input Current .........................................................................5mA
Output Current ....................................................................20mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +165°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
= 3.0V to 5.5V, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at V
DD
= 3.3V and T
A
= +25°C.) (Note 1)
PARAMETER
Power-Supply Range
Average Supply Current
Supply Current During
Conversion
Power-On Reset Threshold
POR Threshold Hysteresis
Temperature Threshold
Accuracy
Temperature Threshold
Hysteresis
Supply Sensitivity of Temperature
Threshold
Output Voltage High
Output Voltage Low
Logic-Low Input Voltage
Logic-High Input Voltage
Input Current
Open-Drain Output Leakage
Current
Conversion Time
Sample Period
Current Sourcing for External
Diode
High level
Low level
V
OH
V
OL
V
IL
V
IH
∆T
TH
V
DD
= 3.3V, T
A
= +25°C, T
RJ
= 0°C to +125°C
(Note 2)
T
A
= 0°C to +100°C, T
RJ
= 0°C to +125°C
T
HYST
T
A
= +25°C, T
RJ
= 0°C to +125°C,
V
DD
= 3.0V to 5.5V
I
SOURCE
= 1mA, MAX6685 T
LOW
only
I
SINK
= 1mA
S1, S2
S1, S2
S1, S2
V
OUT
= 5.5V, T
LOW
and T
HIGH
0.09
0.35
80
8
0.11
0.45
100
10
1.8
10
1
0.13
0.55
120
12
V
DD
-
0.2
0.2
0.4
-1.5
2.0
5.0
0.6
°C
°C/V
V
V
V
V
µA
µA
s
s
µA
POR
V
DD
falling edge
1.0
SYMBOL
V
DD
I
DD
CONDITION
MIN
3.0
200
400
1.5
50
+1.5
TYP
MAX
5.5
500
800
2.0
UNITS
V
µA
µA
V
mV
°C
Note 1:
All parameters are tested at +25°C. Temperature specifications over a range of -40°C to +125°C are guaranteed by design.
Note 2:
T
RJ
is the temperature of the remote-sensing diode junction.
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Dual-Output Remote-Junction
Temperature Switches
Typical Operating Characteristics
(V
DD
= 3.3V, C
S
= 2200pF, T
A
= +25°C, unless otherwise noted. See
Typical Operating Circuits.)
AVERAGE SUPPLY CURRENT
vs. AMBIENT TEMPERATURE
MAX6685 toc01
MAX6685/MAX6686
AVERAGE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6685 toc02
TEMPERATURE TRIP THRESHOLD ERROR
vs. C
S
CAPACITANCE
TEMPERATURE TRIP THRESHOLD ERROR (°C)
MAX6685U40H
S1 = S2 = GND
8
MAX6685 toc03
200
AVERAGE SUPPLY CURRENT (µA)
250
AVERAGE SUPPLY CURRENT (µA)
10
180
200
160
150
6
140
100
4
120
50
2
100
-50
-25
0
25
50
75
100
125
AMBIENT TEMPERATURE (°C)
0
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
0
0
10
20
30
40
50
60
C
S
CAPACITANCE (nF)
UPPER TEMPERATURE TRIP THRESHOLD
ERROR vs. AMBIENT TEMPERATURE
MAX6685 toc04
LOWER TEMPERATURE TRIP THRESHOLD
ERROR vs. AMBIENT TEMPERATURE
LOWER TRIP THRESHOLD ERROR (°C)
1.6
1.2
0.8
0.4
0
-0.4
-0.8
-1.2
-1.6
-2.0
MAX6685U40H
S1 = S2 = V
DD
MAX6685 toc05
2.0
UPPER TRIP THRESHOLD ERROR (°C)
1.6
1.2
0.8
0.4
0
-0.4
-0.8
-1.2
-1.6
-2.0
-50
-25
0
25
50
75
100
MAX6685U40H
T
HIGH
TRIP = +125°C
2.0
125
-50
-25
0
25
50
75
100
125
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
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3
Dual-Output Remote-Junction
Temperature Switches
MAX6685/MAX6686
Pin Description
PIN
MAX6685 MAX6686
1
2
3
1
2
3
NAME
V
DD
GND
DXP
FUNCTION
Power-Supply Input. Bypass to GND with a 0.1µF capacitor.
Ground
This pin connects to the positive (anode) terminal of the external P-N sense junction. It sources
current into the external junction. A 2200pF capacitor should be connected across DXP and DXN.
This pin connects to the negative (cathode) terminal of the external P-N sense junction. It sinks
current from the external junction. A 2200pF capacitor should be connected across DXP and
DXN. DXN must be connected to the GND pin with the shortest possible connection.
Open-Drain, Active-Low Output. T
HIGH
goes low when the temperature exceeds the factory-
programmed upper temperature threshold, either +120°C or +125°C. Connect a pullup resistor
(typically 10kΩ) between T
HIGH
and a positive supply up to 5.5V.
CMOS Push-Pull, Active-High Output. T
LOW
goes HIGH when the temperature exceeds the pin-
programmed lower temperature threshold.
Open-Drain, Active-Low Output. T
LOW
goes LOW when the temperature exceeds the pin-
programmed lower temperature threshold. Connect a pullup resistor (typically 10kΩ) between
T
LOW
and a positive supply up to 5.5V.
Threshold Select Input. Used in conjunction with S2 to set the lower threshold for T
LOW
(Table 1).
It can be connected to V
DD
, GND, or left floating.
Threshold Select Input. Used in conjunction with S1 to set the lower threshold for T
LOW
(Table 1).
It can be connected to V
DD
, GND, or left floating.
4
4
DXN
5
5
T
HIGH
6
—
T
LOW
—
6
T
LOW
7
8
7
8
S1
S2
Detailed Description
The MAX6685/MAX6686 dual-output remote-sensing
junction temperature switches incorporate a precision
remote-junction temperature sensor and two compara-
tors. These devices use an external P-N junction as the
temperature-sensing element (see
Typical Operating
Circuits).
The MAX6685/MAX6686 provide noise immunity by
integration and oversampling of the diode voltage, but
good design practice includes routing the DXP and
DXN lines away from noise sources, such as high-
speed digital lines, switching regulators, inductors, and
transformers. The DXP and DXN traces should be
paired together and surrounded by a ground plane
whenever possible.
The 5°C hysteresis keeps the outputs from “chattering”
when the measured temperature is close to the threshold
temperature. The MAX6685/MAX6686 are available with
preset upper temperature thresholds of +120°C or
+125°C. The lower temperature thresholds are pin pro-
grammable in 5°C increments (Table 1). Two tempera-
ture ranges are available for the lower trip threshold:
+40°C to +80°C and +75°C to +115°C. S1 and S2 pins
must be set to the desired trip temperature before power
is applied to the V
DD
pin. If this is done after the power is
turned on, the lower trip threshold remains set to the
point where S1 and S2 were when power was applied.
Applications Information
Remote-Diode Selection
The MAX6685/MAX6686 are optimized to measure the
die temperature of CPUs and other ICs that have on-chip
temperature-sensing diodes. These on-chip diodes are
substrate PNPs with their collectors grounded. Connect
the base of the PNP to DXN and the emitter to DXP. When
using a discrete, diode-connected NPN or PNP as a
sensing diode, use a good-quality small-signal device.
Examples are listed in Table 2. Tight specifications for for-
ward current gain indicate the manufacturer has good
process controls and that the devices have consistent
V
be
characteristics. Always use a transistor for the sens-
ing junction; diodes do not work.
4
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Dual-Output Remote-Junction
Temperature Switches
MAX6685/MAX6686
Table 1. Lower Temperature Trip Threshold Selection
MAX6685AUA40L
MAX6685AUA40H
MAX6686AUA40L
MAX6686AUA40H
LOWER TEMPERATURE
TRIP THRESHOLD (°C)
GND
GND
GND
FLOAT
FLOAT
FLOAT
V
DD
V
DD
V
DD
GND
FLOAT
V
DD
GND
FLOAT
V
DD
GND
FLOAT
V
DD
+40
+45
+50
+55
+60
+65
+70
+75
+80
MAX6685AUA75L
MAX6685AUA75H
MAX6686AUA75L
MAX6686AUA75H
LOWER TEMPERATURE
TRIP THRESHOLD (°C)
+75
+80
+85
+90
+95
+100
+105
+110
+115
S1
S2
Noise-Filtering Capacitors
A quality ceramic capacitor must be connected across
the DXP/DXN inputs to maintain temperature threshold
accuracy by filtering out noise. The capacitor should be
located physically close to the DXP/DXN pins and
should typically have a value of 2200pF. Larger capaci-
tor values can cause temperature measurement errors.
A 50% variation from the recommended capacitor
value can cause up to ±1°C error.
Table 2. Sensor Transistor Manufacturers
MANUFACTURER
Central Semiconductor (USA)
ON Semiconductor (USA)
Rohm Semiconductor (Japan)
Samsung (Korea)
Siemens (Germany)
MODEL NO.
CMPT3904
2N3904, 2N3906
SST3904
KST3904-TF
SMBT3904
Note:
Discrete transistors must be diode connected (base
shorted to collector).
V
DD
V
DD
T
HIGH
+120°C OR +125°C
N
DXP
DXN
REMOTE
TEMPERATURE
CONVERTER
DIGITAL
DRIVER
T
HIGH
T
HIGH
+120°C OR +125°C
N
DXP
DXN
REMOTE
TEMPERATURE
CONVERTER
N
T
LOW
+40°C TO +115°C
T
HIGH
T
LOW
S1
S2
T
LOW
T
LOW
+40°C TO +115°C
S1
S2
GND
MAX6685
GND
MAX6686
Figure 1. MAX6685 Functional Diagram
Figure 2. MAX6686 Functional Diagram
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