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 (THIGH
and TLOW). THIGH asserts a logic signal when the remote
temperature crosses the factory-programmed, +120°C, or
+125°C upper trip threshold. TLOW 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.
THIGH is an open-drain, active-low output for both the
MAX6685 and the MAX6686. TLOW 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.
Applications
Features
♦Pin-Programmed Lower Temperature Threshold
from +40°C to +80°C or +75°C to +115°C
(5°C Increments)
♦Preset Upper Threshold: +120°C or +125°C
♦Open-Drain, Active-Low Output for Upper
Temperature Alarm
♦CMOS Push-Pull, Active-High or Open-Drain,
Active-Low Output for Lower Temperature Alarm
♦1.5°C Accuracy
♦3.0V to 5.5V, 200µA Supply
♦8-Pin µMAX Package
MAX6685/MAX6686
Dual-Output Remote-Junction
Temperature Switches
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
MAX6685
CS
12V
GND
CPU
S1
DXN
S2
3.3V TO SYSTEM
SHUTDOWN
N
TLOW
DXP
VDD THIGH
MAX6686
CS
GND
CPU
S1
DXN
S2
3.3V
TO SYSTEM
SHUTDOWN
TO CLOCK
THROTTLE
CONTROL
TLOW
DXP
VDD THIGH
Typical Operating Circuits
19-2459; Rev 2; 4/03
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.
PART TLOW
OUTPUT
TLOW TRIP
RANGE (0°C)
THIGH TRIP
THRESHOLD (0°C) PIN-PACKAGE
MAX6685AU40L Push-pull, active high +40°C to +80°C +120°C 8 µMAX
MAX6685AU40H Push-pull, active high +40°C to +80°C +125°C 8 µMAX
MAX6685AU75L Push-pull, active high +75°C to +115°C +120°C 8 µMAX
MAX6685AU75H Push-pull, active high +75°C to +115°C +125°C 8 µMAX
MAX6686AU40L Open drain, active low +40°C to +80°C +120°C 8 µMAX
MAX6686AU40H Open drain, active low +40°C to +80°C +125°C 8 µMAX
MAX6686AU75L Open drain, active low +75°C to +115°C +120°C 8 µMAX
MAX6686AU75H Open drain, active low +75°C to +115°C +125°C 8 µMAX
Pin Configurations appear at end of data sheet.
CPU Temperature
Protection
Fan Control
Multichip Modules
FPGA Temperature
Protection
MAX6685/MAX6686
Dual-Output Remote-Junction
Temperature Switches
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD = 3.0V to 5.5V, TA= -40°C to +125°C, unless otherwise noted. Typical values are at VDD = 3.3V and TA= +25°C.) (Note 1)
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.
Voltages Referenced to GND
VDD, TLOW, THIGH.....................................................-0.3V to +6V
DXN .......................................................................-0.3V to +0.8V
All Other Pins..............................................-0.3V to (VDD + 0.3V)
Input Current .........................................................................5mA
Output Current ....................................................................20mA
Continuous Power Dissipation (TA = +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
PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS
Power-Supply Range VDD 3.0 5.5 V
Average Supply Current IDD 200 500 µA
Supply Current During
Conversion 400 800 µA
Power-On Reset Threshold POR VDD falling edge 1.0 1.5 2.0 V
POR Threshold Hysteresis 50 mV
VDD = 3.3V, TA = +25°C, TRJ = 0°C to +125°C
(Note 2) -1.5 +1.5
Temperature Threshold
Accuracy ∆TTH
TA = 0°C to +100°C, TRJ = 0°C to +125°C 2.0
°C
Temperature Threshold
Hysteresis THYST 5.0 °C
Supply Sensitivity of Temperature
Threshold
TA = +25°C, TRJ = 0°C to +125°C,
VDD = 3.0V to 5.5V 0.6 °C/V
Output Voltage High VOH ISOURCE = 1mA, MAX6685 TLOW only VDD -
0.2 V
Output Voltage Low VOL ISINK = 1mA 0.2 V
Logic-Low Input Voltage VIL S1, S2 0.4 V
Logic-High Input Voltage VIH S1, S2 1.8 V
Input Current S1, S2 10 µA
Open-Drain Output Leakage
Current VOUT = 5.5V, TLOW and THIGH 1µA
Conversion Time 0.09 0.11 0.13 s
Sample Period 0.35 0.45 0.55 s
High level 80 100 120
Current Sourcing for External
Diode Low level 8 10 12 µA
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: TRJ is the temperature of the remote-sensing diode junction.
MAX6685/MAX6686
Dual-Output Remote-Junction
Temperature Switches
_______________________________________________________________________________________ 3
AVERAGE SUPPLY CURRENT
vs. AMBIENT TEMPERATURE
MAX6685 toc01
AMBIENT TEMPERATURE (°C)
AVERAGE SUPPLY CURRENT (µA)
1007550250-25
120
140
160
180
200
100
-50 125
AVERAGE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6685 toc02
SUPPLY VOLTAGE (V)
AVERAGE SUPPLY CURRENT (µA)
5.04.54.03.5
50
100
150
200
250
0
3.0 5.5
TEMPERATURE TRIP THRESHOLD ERROR
vs. CS CAPACITANCE
MAX6685 toc03
CS CAPACITANCE (nF)
TEMPERATURE TRIP THRESHOLD ERROR (°C)
5040302010
2
4
6
8
10
0
060
MAX6685U40H
S1 = S2 = GND
UPPER TEMPERATURE TRIP THRESHOLD
ERROR vs. AMBIENT TEMPERATURE
MAX6685 toc04
AMBIENT TEMPERATURE (°C)
UPPER TRIP THRESHOLD ERROR (°C)
1007525 500-25
-1.6
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1.6
2.0
-2.0
-50 125
MAX6685U40H
THIGH TRIP = +125°C
LOWER TEMPERATURE TRIP THRESHOLD
ERROR vs. AMBIENT TEMPERATURE
MAX6685 toc05
AMBIENT TEMPERATURE (°C)
LOWER TRIP THRESHOLD ERROR (°C)
1007525 500-25
-1.6
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1.6
2.0
-2.0
-50 125
MAX6685U40H
S1 = S2 = VDD
Typical Operating Characteristics
(VDD = 3.3V, CS= 2200pF, TA= +25°C, unless otherwise noted. See Typical Operating Circuits.)
MAX6685/MAX6686
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 VDD 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
Vbe characteristics. Always use a transistor for the sens-
ing junction; diodes do not work.
Dual-Output Remote-Junction
Temperature Switches
4 _______________________________________________________________________________________
Pin Description
PIN
MAX6685 MAX6686 NAME FUNCTION
11V
DD Power-Supply Input. Bypass to GND with a 0.1µF capacitor.
2 2 GND Ground
3 3 DXP 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.
4 4 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.
55T
HIGH
Open-Drain, Active-Low Output. THIGH 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 THIGH and a positive supply up to 5.5V.
6—T
LOW CMOS Push-Pull, Active-High Output. TLOW goes HIGH when the temperature exceeds the pin-
programmed lower temperature threshold.
—6T
LOW
Open-Drain, Active-Low Output. TLOW goes LOW when the temperature exceeds the pin-
programmed lower temperature threshold. Connect a pullup resistor (typically 10kΩ) between
TLOW and a positive supply up to 5.5V.
77S1
Threshold Select Input. Used in conjunction with S2 to set the lower threshold for TLOW (Table 1).
It can be connected to VDD, GND, or left floating.
88S2
Threshold Select Input. Used in conjunction with S1 to set the lower threshold for TLOW (Table 1).
It can be connected to VDD, GND, or left floating.
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.
MAX6685/MAX6686
Dual-Output Remote-Junction
Temperature Switches
_______________________________________________________________________________________ 5
N
TLOW
THIGH
DXN
S2
S1
GND
THIGH
+120°C OR +125°C
REMOTE
TEMPERATURE
CONVERTER
TLOW
+40°C TO +115°C
DXP
VDD
MAX6685
DIGITAL
DRIVER
Figure 1. MAX6685 Functional Diagram
N
N
TLOW
THIGH
DXN
S2
S1
GND
THIGH
+120°C OR +125°C
REMOTE
TEMPERATURE
CONVERTER
TLOW
+40°C TO +115°C
DXP
VDD
MAX6686
Figure 2. MAX6686 Functional Diagram
MAX6685AUA40L
MAX6685AUA40H
MAX6686AUA40L
MAX6686AUA40H
MAX6685AUA75L
MAX6685AUA75H
MAX6686AUA75L
MAX6686AUA75H
S1 S2
LOWER TEMPERATURE
TRIP THRESHOLD (°C)
LOWER TEMPERATURE
TRIP THRESHOLD (°C)
GND GND +40 +75
GND FLOAT +45 +80
GND VDD +50 +85
FLOAT GND +55 +90
FLOAT FLOAT +60 +95
FLOAT VDD +65 +100
VDD GND +70 +105
VDD FLOAT +75 +110
VDD VDD +80 +115
Table 1. Lower Temperature Trip Threshold Selection
MANUFACTURER MODEL NO.
Central Semiconductor (USA) CMPT3904
ON Semiconductor (USA) 2N3904, 2N3906
Rohm Semiconductor (Japan) SST3904
Samsung (Korea) KST3904-TF
Siemens (Germany) SMBT3904
Table 2. Sensor Transistor Manufacturers
Note: Discrete transistors must be diode connected (base
shorted to collector).
MAX6685/MAX6686
Dual-Output Remote-Junction
Temperature Switches
6 _______________________________________________________________________________________
TOP VIEW
TLOW
THIGH
DXN
1
2
8
7
S2
S1GND
DXP
VDD
µMAX
3
4
6
5
MAX6685
TLOW
THIGH
DXN
1
2
8
7
S2
S1GND
DXP
VDD
µMAX
3
4
6
5
MAX6686
Pin Configurations Chip Information
TRANSISTOR COUNT: 7765
PROCESS: BiCMOS
MAX6685/MAX6686
Dual-Output Remote-Junction
Temperature Switches
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 7
© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
8LUMAXD.EPS
PACKAGE OUTLINE, 8L uMAX/uSOP
1
1
21-0036 J
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
MAX
0.043
0.006
0.014
0.120
0.120
0.198
0.026
0.007
0.037
0.0207 BSC
0.0256 BSC
A2 A1
c
eb
A
L
FRONT VIEW SIDE VIEW
E H
0.6±0.1
0.6±0.1
ÿ 0.50±0.1
1
TOP VIEW
D
8
A2 0.030
BOTTOM VIEW
16∞
S
b
L
H
E
D
e
c
0∞
0.010
0.116
0.116
0.188
0.016
0.005
8
4X S
INCHES
-
A1
A
MIN
0.002
0.950.75
0.5250 BSC
0.25 0.36
2.95 3.05
2.95 3.05
4.78
0.41
0.65 BSC
5.03
0.66
6∞0∞
0.13 0.18
MAX
MIN
MILLIMETERS
- 1.10
0.05 0.15
α
α
DIM
