MAX31855SASA+T [MAXIM]
Cold-Junction Compensated Thermocouple-to-Digital Converter; 冷端补偿热电偶至数字转换器
| 型号： | MAX31855SASA+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Cold-Junction Compensated Thermocouple-to-Digital Converter |
| 文件： | 总13页 (文件大小：1215K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-5793; Rev 2; 2/12
General Description
Features
The MAX31855 performs cold-junction compensation
and digitizes the signal from a K-, J-, N-, T-, S-, R-, or
E-type thermocouple. The data is output in a signed
14-bit, SPI-compatible, read-only format. This converter
resolves temperatures to 0.25NC, allows readings as high
as +1800NC and as low as -270NC, and exhibits thermo-
couple accuracy of 2NC for temperatures ranging from
-200NC to +700NC for K-type thermocouples. For full
range accuracies and other thermocouple types, see the
Thermal Characteristics specifications.
S Cold-Junction Compensation
S 14-Bit, 0.25NC Resolution
S Versions Available for K-, J-, N-, T-, S-, R-, and
E-Type Thermocouples (see Table 1)
S Simple SPI-Compatible Interface (Read-Only)
S Detects Thermocouple Shorts to GND or V
CC
S Detects Open Thermocouple
Ordering Information appears at end of data sheet.
Applications
Industrial
Appliances
HVAC
For related parts and recommended products to use with this part,
refer to: www.maxim-ic.com/MAX31855.related
Automotive
Typical Application Circuit
V
CC
0.1µF
MAX31855
GND
MICROCONTROLLER
SO
MISO
SCK
SS
SCK
CS
T+
T-
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For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
ABSOLUTE MAXIMUM RATINGS
Supply Voltage Range (V
to GND)..................-0.3V to +4.0V
Operating Temperature Range........................ -40NC to +125NC
Junction Temperature .....................................................+150NC
Storage Temperature Range .......................... -65NC to +150NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) .....................................+260NC
CC
All Other Pins............................................ -0.3V to (V
+ 0.3V)
CC
Continuous Power Dissipation (T = +70NC)
A
SO (derate 5.9mW/NC above +70NC).......................470.6mW
ESD Protection (All Pins, Human Body Model)................... 2ꢀV
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-
tion 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)
SO
Junction-to-Ambient Thermal Resistance (B ) ........170NC/W
JA
Junction-to-Case Thermal Resistance (B )...............40NC/W
JC
Note 1: Pacꢀage thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on pacꢀage thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
RECOMMENDED OPERATING CONDITIONS
(T = -40NC to +125NC, unless otherwise noted.)
A
PARAMETER
Power-Supply Voltage
Input Logic 0
SYMBOL
CONDITIONS
MIN
3.0
TYP
MAX
3.6
UNITS
V
(Note 2)
3.3
V
V
CC
V
-0.3
+0.8
IL
V
CC
0.3
+
Input Logic 1
V
2.1
V
IH
DC ELECTRICAL CHARACTERISTICS
(3.0V P V
P 3.6V, T = -40NC to +125NC, unless otherwise noted.)
A
CC
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Power-Supply Current
I
900
1500
FA
CC
T
= -40NC to +125NC, 100mV across the
A
Thermocouple Input Bias Current
Power-Supply Rejection
-100
+100
2.5
nA
NC/V
V
thermocouple inputs
-0.3
2
Power-On Reset Voltage
Threshold
V
(Note 3)
POR
Power-On Reset Voltage
Hysteresis
0.2
V
V
CC
0.4
-
Output High Voltage
Output Low Voltage
V
I
I
= -1.6mA
= 1.6mA
V
V
OH
OUT
V
0.4
OL
OUT
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
THERMAL CHARACTERISTICS
(3.0V P V
P 3.6V, T = -40NC to +125NC, unless otherwise noted.) (Note 4)
A
CC
PARAMETER
SYMBOL
CONDITIONS
= -200NC to +700NC,
= -20NC to +85NC (Note 3)
MIN
TYP
MAX
UNITS
T
T
THERMOCOUPLE
-2
+2
A
MAX31855K Thermocouple
Temperature Gain and Offset
Error (41.276FV/NC nominal
sensitivity) (Note 4)
T
T
= +700NC to +1350NC,
THERMOCOUPLE
-4
-6
-2
-4
-2
-4
-6
-2
-4
-2
-3
-5
-2
-4
-6
-2
-4
-6
+4
+6
+2
+4
+2
+4
+6
+2
+4
+2
+3
+5
+2
+4
+6
+2
+4
+6
NC
= -20NC to +85NC (Note 3)
A
T
T
= -270NC to +1372NC,
THERMOCOUPLE
= -40NC to +125NC (Note 3)
A
T
T
= -210NC to +750NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
MAX31855J Thermocouple
Temperature Gain and Offset
Error (57.953FV/NC nominal
sensitivity) (Note 4)
A
NC
NC
NC
NC
T
T
= -210NC to +1200NC,
THERMOCOUPLE
= -40NC to +125NC (Note 3)
A
T
T
= -200NC to +700NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
A
MAX31855N Thermocouple
Temperature Gain and Offset
Error (36.256FV/NC nominal
sensitivity) (Note 4)
T
T
= +700NC to +1300NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
A
T
T
= -270NC to +1300NC,
THERMOCOUPLE
= -40NC to +125NC (Note 3)
A
T
T
= -270NC to +400NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
MAX31855T Thermocouple
Temperature Gain and Offset
Error (52.18FV/NC nominal
sensitivity) (Note 4)
A
T
T
= -270NC to +400NC,
THERMOCOUPLE
= -40NC to +125NC (Note 3)
A
T
T
= -200NC to +700NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
A
MAX31855E Thermocouple
Temperature Gain and Offset
Error (76.373FV/NC nominal
sensitivity) (Note 4)
T
T
= +700NC to +1000NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
A
T
T
= -270NC to +1000NC,
THERMOCOUPLE
= -40NC to +125NC (Note 3)
A
T
T
= -50NC to +700NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
A
MAX31855R Thermocouple
Temperature Gain and Offset
Error (10.506FV/NC nominal
sensitivity) (Note 4)
T
T
= +700NC to +1768NC,
THERMOCOUPLE
NC
NC
= -20NC to +85NC (Note 3)
A
T
T
= -50NC to +1768NC,
THERMOCOUPLE
= -40NC to +125NC (Note 3)
A
T
T
= -50NC to +700NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
A
MAX31855S Thermocouple
Temperature Gain and Offset
Error (9.587FV/NC nominal
sensitivity) (Note 4)
T
T
= +700NC to +1768NC,
THERMOCOUPLE
= -20NC to +85NC (Note 3)
A
T
T
= -50NC to +1768NC,
THERMOCOUPLE
= -40NC to +125NC (Note 3)
A
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
THERMAL CHARACTERISTICS (continued)
(3.0V P V
P 3.6V, T = -40NC to +125NC, unless otherwise noted.) (Note 4)
A
CC
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Thermocouple Temperature Data
Resolution
0.25
NC
T
T
= -20NC to +85NC (Note 3)
= -40NC to +125NC (Note 3)
-2
-3
+2
+3
Internal Cold-Junction
Temperature Error
A
A
NC
NC
Cold-Junction Temperature Data
Resolution
T
= -40NC to +125NC
0.0625
70
A
Temperature Conversion Time
(Thermocouple, Cold Junction,
Fault Detection)
t
(Note 5)
(Note 6)
100
ms
ms
CONV
Thermocouple Conversion
Power-Up Time
t
200
CONV_PU
SERIAL-INTERFACE TIMING CHARACTERISTICS
(See Figure 1 and Figure 2.)
PARAMETER
Input Leaꢀage Current
Input Capacitance
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
µA
pF
I
(Note 7)
-1
+1
LEAK
C
8
IN
Serial-Clocꢀ Frequency
SCK Pulse-High Width
SCK Pulse-Low Width
SCK Rise and Fall Time
f
5
MHz
ns
SCL
t
100
100
CH
t
ns
CL
200
ns
t
100
100
ns
CS Fall to SCK Rise
CSS
ns
SCK to CS Hold
t
100
40
ns
CS Fall to Output Enable
CS Rise to Output Disable
SCK Fall to Output Data Valid
DV
t
ns
TR
t
40
ns
DO
(Note 3)
200
ns
CS Inactive Time
Note 2: All voltages are referenced to GND. Currents entering the IC are specified positive, and currents exiting the IC are negative.
Note 3: Guaranteed by design; not production tested.
Note 4: Not including cold-junction temperature error or thermocouple nonlinearity.
Note 5: Specification is 100% tested at T = +25NC. Specification limits over temperature (T = T
to T ) are guaranteed by
MAX
A
A
MIN
design and characterization; not production tested.
Note 6: Because the thermocouple temperature conversions begin at V
, depending on V
slew rates, the first thermocouple
POR
CC
temperature conversion may not produce an accurate result. Therefore, the t
specification is required after V
is
CONV_PU
CC
greater than V
to guarantee a valid thermocouple temperature conversion result.
CCMIN
Note 7: For all pins except T+ and T- (see the Thermocouple Input Bias Current parameter in the DC Electrical Characteristics
table).
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Serial-Interface Diagrams
CS
SCK
SO
D0
D31
D7
D6
D4
D2
D8
D5
D3
D1
Figure 1. Serial-Interface Protocol
t
CSS
CS
t
t
CL
CH
SCK
SO
t
DV
t
DO
t
TR
D31
D3
D2
D1
D0
Figure 2. Serial-Interface Timing
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Typical Operating Characteristics
(V
CC
= +3.3V, T = +25NC, unless otherwise noted.)
A
INTERNAL TEMPERATURE SENSOR
ACCURACY
SUPPLY CURRENT vs. TEMPERATURE
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
V
= 3.3V
CC
V
= 3.6V
CC
NOTE: THIS DATA WAS TAKEN
IN PRECISION BATH SO HIGH
TEMPERATURE LIMIT IS 90°C
V
= 3.3V
CC
V
= 3.0V
CC
-0.1
-0.2
-40 -20
0
20 40 60 80 100 120
TEMPERATURE (°C)
-40 -20
0
20
40
60
80 100
TEMPERATURE (°C)
ADC ACCURACY vs. ADC INPUT VOLTAGE
ACROSS TEMPERATURE
ADC ACCURACY vs. ADC INPUT VOLTAGE
ACROSS V
CC
0.3
0.2
0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
-0.9
-1.0
AT -40°C
V
= 3.0V
CC
0.1
0
V
= 3.3V
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
AT +85°C
CC
V
= 3.6V
CC
AT +25°C
V
= 3.3V
INTERNAL TEMPERATURE = +25°C
20 40
ADC INPUT VOLTAGE (mV)
CC
0
20
40
60
0
60
ADC INPUT VOLTAGE (mV)
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Pin Description
Pin Configuration
PIN
NAME
FUNCTION
1
GND
Ground
TOP VIEW
Thermocouple Input. See Table 1. Do
not connect to GND.
2
T-
+
GND
T-
1
2
3
4
8
7
6
5
DNC
SO
3
4
5
T+
Thermocouple Input. See Table 1.
Power-Supply Voltage
V
CC
MAX31855
SCK
Serial-Clocꢀ Input
T+
CS
Active-Low Chip Select. Set CS low to
enable the serial interface.
6
CS
V
CC
SCK
7
8
SO
Serial-Data Output
Do Not Connect
SO
DNC
Block Diagram
V
CC
V
CC
S5
S4
SCK
SO
COLD-JUNCTION
COMPENSATION
DIGITAL
CONTROL
MAX31855
CS
T+
ADC
T-
S1
S2
FAULT
DETECTION
GND
REFERENCE
VOLTAGE
S3
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
for the difference between the thermocouple cold-
Detailed Description
junction side (device ambient temperature) and a 0NC
virtual reference. For a K-type thermocouple, the volt-
age changes by about 41FV/NC, which approximates
the thermocouple characteristic with the following linear
equation:
The MAX31855 is a sophisticated thermocouple-to-
digital converter with a built-in 14-bit analog-to-digital
converter (ADC). The device also contains cold-junction
compensation sensing and correction, a digital control-
ler, an SPI-compatible interface, and associated control
logic. The device is designed to worꢀ in conjunction
with an external microcontroller (FC) in thermostatic,
process-control, or monitoring applications. The device
is available in several versions, each optimized and
trimmed for a specific thermocouple type (K, J, N, T, S,
R, or E.). The thermocouple type is indicated in the suffix
of the part number (e.g., MAX31855K). See the Ordering
Information table for all options.
V
= (41.276FV/NC) x (T - T
)
OUT
R
AMB
where V
is the thermocouple output voltage (FV), T
R
OUT
is the temperature of the remote thermocouple junction
(NC), and T is the temperature of the device (NC).
AMB
Other thermocouple types use a similar straight-line
approximation but with different gain terms. Note that the
MAX31855 assumes a linear relationship between tem-
perature and voltage. Because all thermocouples exhibit
some level of nonlinearity, apply appropriate correction
to the device’s output data.
Temperature Conversion
The device includes signal-conditioning hardware to
convert the thermocouple’s signal into a voltage com-
patible with the input channels of the ADC. The T+ and
T- inputs connect to internal circuitry that reduces the
introduction of noise errors from the thermocouple wires.
Cold-Junction Compensation
The function of the thermocouple is to sense a difference
in temperature between two ends of the thermocouple
wires. The thermocouple’s “hot” junction can be read
across the operating temperature range (Table 1). The
reference junction, or “cold” end (which should be at
Before converting the thermoelectric voltages into equiv-
alent temperature values, it is necessary to compensate
Table 1. Thermocouple Wire Connections and Nominal Sensitivities
COLD-JUNCTION
SENSITIVITY (µV/°C)
(0NC TO +70NC)
TYPE
T- WIRE
T+ WIRE
TEMP RANGE (°C)
SENSITIVITY (µV/°C)
41.276
(0NC to +1000NC)
K
J
Alumel
Constantan
Nisil
Chromel
Iron
-270 to +1372
-210 to +1200
-270 to + 1300
+50 to +1768
-270 to +400
-270 to +1000
-50 to +1768
40.73
52.136
27.171
6.181
57.953
(0NC to +750NC)
36.256
(0NC to +1000NC)
N
S
T
E
R
Nicrosil
9.587
(0NC to +1000NC)
Platinum
Constantan
Constantan
Platinum
Platinum/Rhodium
Copper
52.18
(0NC to +400NC)
41.56
76.373
(0NC to +1000NC)
Chromel
44.123
6.158
10.506
(0NC to +1000NC)
Platinum/Rhodium
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
the same temperature as the board on which the device
During fault detection, the connections from the exter-
nal thermocouple and cold-junction compensation cir-
cuit to the ADC are opened (switches S4 and S5). The
internal ground reference on T- is also opened (switch
S3). The connections to the internal fault-detection cir-
cuit are closed (switch S1 and S2). The fault-detection
is mounted) can range from -55NC to +125NC. While the
temperature at the cold end fluctuates, the device con-
tinues to accurately sense the temperature difference at
the opposite end.
The device senses and corrects for the changes in
the reference junction temperature with cold-junction
compensation. It does this by first measuring its internal
die temperature, which should be held at the same tem-
perature as the reference junction. It then measures the
voltage from the thermocouple’s output at the reference
junction and converts this to the noncompensated ther-
mocouple temperature value. This value is then added
to the device’s die temperature to calculate the thermo-
couple’s “hot junction” temperature. Note that the “hot
junction” temperature can be lower than the cold junction
(or reference junction) temperature.
circuit tests for shorted connections to V
or GND on
CC
the T+ and T- inputs, as well as looꢀing for an open
thermocouple condition. Bits D0, D1, and D2 of the
output data are normally low. Bit D2 goes high to indi-
cate a thermocouple short to V , bit D1 goes high to
CC
indicate a thermocouple short to GND, and bit D0 goes
high to indicate a thermocouple open circuit. If any of
these conditions exists, bit D16 of the SO output data,
which is normally low, also goes high to indicate that a
fault has occurred.
Serial Interface
Optimal performance from the device is achieved when
the thermocouple cold junction and the device are at
the same temperature. Avoid placing heat-generating
devices or components near the MAX31855 because this
could produce cold-junction-related errors.
The Typical Application Circuit shows the device inter-
faced with a microcontroller. In this example, the device
processes the reading from the thermocouple and
transmits the data through a serial interface. Drive CS
low and apply a clocꢀ signal at SCK to read the results
at SO. Conversions are always being performed in the
bacꢀground. The fault and temperature data are only be
updated when CS is high.
Conversion Functions
CONV
During the conversion time, t
, three functions are
performed: the temperature conversion of the internal
cold-junction temperature, the temperature conversion of
the external thermocouple, and the detection of thermo-
couple faults.
Drive CS low to output the first bit on the SO pin. A
complete serial-interface read of the cold-junction com-
pensated thermocouple temperature requires 14 clocꢀ
cycles. Thirty-two clocꢀ cycles are required to read both
the thermocouple and reference junction temperatures
(Table 2 and Table 3.) The first bit, D31, is the thermo-
couple temperature sign bit, and is presented to the SO
When executing the temperature conversion for the inter-
nal cold-junction compensation circuit, the connection to
signal from the external thermocouple is opened (switch
S4) and the connection to the cold-junction compensa-
tion circuit is closed (switch S5). The internal T- reference
to ground is still maintained (switch S3 is closed) and
the connections to the fault-detection circuit are open
(switches S1 and S2).
pin within t
of the falling edge of CS. Bits D[30:18]
DV
contain the converted temperature in the order of MSB
to LSB, and are presented to the SO pin within t of the
D0
falling edge of SCK. Bit D16 is normally low and goes
high when the thermocouple input is open or shorted to
When executing the temperature conversion of the
external thermocouple, the connections to the internal
fault-detection circuit are opened (switches S1 and S2 in
the Block Diagram) and the switch connecting the cold-
junction compensation circuit is opened (switch S5). The
internal ground reference connection (switch S3) and
the connection to the ADC (switch S4) are closed. This
allows the ADC to process the voltage detected across
the T+ and T- terminals.
GND or V . The reference junction temperature data
CC
begins with D15. CS can be taꢀen high at any point while
clocꢀing out conversion data. If T+ and T- are uncon-
nected, the thermocouple temperature sign bit (D31) is
0, and the remainder of the thermocouple temperature
value (D[30:18]) is 1.
Figure 1 and Figure 2 show the serial-interface timing
and order. Table 2 and Table 3 show the SO output bit
weights and functions.
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Table 2. Memory Map—Bit Weights and Functions
14-BIT THERMOCOUPLE
TEMPERATURE DATA
FAULT
BIT
12-BIT INTERNAL TEMPERATURE
DATA
SCV
BIT
SCG
BIT
OC
BIT
RES
RES
BIT
D31
Sign
D30
…
…
D18
D17
D16
D15
Sign
D14
…
D4
D3
D2
D1
D0
1 =
Short
to
1 =
Short
to
MSB
1 =
10
-2
-4
MSB 2
LSB 2
1 =
LSB 2
6
VALUE
Reserved
2
…
Reserved
Open
Circuit
(1024NC)
(0.25NC)
Fault
(0.0625NC)
(64NC)
V
GND
CC
Table 3. Memory Map—Descriptions
BIT
D[31:18]
D17
NAME
DESCRIPTION
14-Bit Thermocouple
Temperature Data
These bits contain the signed 14-bit thermocouple temperature value. See Table 4.
This bit always reads 0.
Reserved
This bit reads at 1 when any of the SCV, SCG, or OC faults are active. Default value
is 0.
D16
Fault
12-Bit Internal Temperature
Data
These bits contain the signed 12-bit value of the reference junction temperature.
See Table 5.
D[15:4]
D3
D2
D1
D0
Reserved
SCV Fault
SCG Fault
OC Fault
This bit always reads 0.
This bit is a 1 when the thermocouple is short-circuited to V . Default value is 0.
CC
This bit is a 1 when the thermocouple is short-circuited to GND. Default value is 0.
This bit is a 1 when the thermocouple is open (no connections). Default value is 0.
Table 4. Thermocouple Temperature Data
Format
Table 5. Reference Junction Temperature
Data Format
TEMPERATURE
DIGITAL OUTPUT
(D[31:18])
TEMPERATURE
DIGITAL OUTPUT
(D[15:4])
(NC)
(NC)
+1600.00
+1000.00
+100.75
+25.00
0.00
0110 0100 0000 00
0011 1110 1000 00
0000 0110 0100 11
0000 0001 1001 00
0000 0000 0000 00
1111 1111 1111 11
1111 1111 1111 00
1111 0000 0110 00
+127.0000
+100.5625
+25.0000
0.0000
0111 1111 0000
0110 0100 1001
0001 1001 0000
0000 0000 0000
1111 1111 1111
1111 1111 0000
1110 1100 0000
1100 1001 0000
-0.0625
-0.25
-1.0000
-1.00
-20.0000
-55.0000
-250.00
Note: The practical temperature ranges vary with the
thermocouple type.
���������������������������������������������������������������� Maxim Integrated Products 10
MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
The thermocouple system’s accuracy can also be
Applications Information
improved by following these precautions:
Noise Considerations
Because of the small signal levels involved, thermocou-
ple temperature measurement is susceptible to power-
supply coupled noise. The effects of power-supply noise
can be minimized by placing a 0.1FF ceramic bypass
•ꢀ Useꢀtheꢀlargestꢀwireꢀpossibleꢀthatꢀdoesꢀnotꢀshuntꢀheatꢀ
away from the measurement area.
•ꢀ Ifꢀ aꢀ smallꢀ wireꢀ isꢀ required,ꢀ useꢀ itꢀ onlyꢀ inꢀ theꢀ regionꢀ
of the measurement, and use extension wire for the
region with no temperature gradient.
capacitor close to the V
pin of the device and to GND.
CC
•ꢀ Avoidꢀ mechanicalꢀ stressꢀ andꢀ vibration,ꢀ whichꢀ couldꢀ
The input amplifier is a low-noise amplifier designed to
enable high-precision input sensing. Keep the thermo-
couple and connecting wires away from electrical noise
sources. It is strongly recommended to add a 10nF
ceramic surface-mount differential capacitor, placed
across the T+ and T- pins, in order to filter noise on the
thermocouple lines.
strain the wires.
•ꢀ Whenꢀusingꢀlongꢀthermocoupleꢀwires,ꢀuseꢀaꢀtwistedꢀ
pair extension wire.
•ꢀ Avoidꢀsteepꢀtemperatureꢀgradients.
•ꢀ Tryꢀtoꢀuseꢀtheꢀthermocoupleꢀwireꢀwellꢀwithinꢀitsꢀtem-
perature rating.
Thermal Considerations
Self-heating degrades the device’s temperature measure-
ment accuracy in some applications. The magnitude of the
temperature errors depends on the thermal conductivity
of the device pacꢀage, the mounting technique, and the
effects of airflow. Use a large ground plane to improve the
device’s temperature measurement accuracy.
•ꢀ Useꢀtheꢀproperꢀsheathingꢀmaterialꢀinꢀhostileꢀenviron-
ments to protect the thermocouple wire.
•ꢀ Useꢀextensionꢀwireꢀonlyꢀatꢀlowꢀtemperaturesꢀandꢀonlyꢀ
in regions of small gradients.
•ꢀ Keepꢀanꢀeventꢀlogꢀandꢀaꢀcontinuousꢀrecordꢀofꢀthermo-
couple resistance.
���������������������������������������������������������������� Maxim Integrated Products 11
MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Ordering Information
PART
MAX31855KASA+
MAX31855KASA+T
MAX31855JASA+
MAX31855JASA+T
MAX31855NASA+
MAX31855NASA+T
MAX31855SASA+
MAX31855SASA+T
MAX31855TASA+
MAX31855TASA+T
MAX31855EASA+
MAX31855EASA+T
MAX31855RASA+
MAX31855RASA+T
THERMOCOUPLE TYPE
MEASURED TEMP RANGE
-200NC to +1350NC
-200NC to +1350NC
-40NC to +750NC
PIN-PACKAGE
8 SO
K
K
J
8 SO
8 SO
J
-40NC to +750NC
8 SO
N
N
S
S
T
-200NC to + 1300NC
-200NC to + 1300NC
+50NC to +1600NC
+50NC to +1600NC
-250NC to +400NC
-250NC to +400NC
-40NC to +900NC
8 SO
8 SO
8 SO
8 SO
8 SO
T
8 SO
E
E
R
R
8 SO
-40NC to +900NC
8 SO
-50NC to +1770NC
-50NC to +1770NC
8 SO
8 SO
Note: All devices are specified over the -40°C to +125°C operating temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Package Information
For the latest pacꢀage outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or
“-” in the pacꢀage code indicates RoHS status only. Pacꢀage drawings may show a different suffix character, but the drawing pertains
to the pacꢀage regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
OUTLINE NO.
21-0041
LAND PATTERN NO.
90-0096
8 SO
S8+4
���������������������������������������������������������������� Maxim Integrated Products 12
MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Revision History
REVISION REVISION
PAGES
DESCRIPTION
CHANGED
NUMBER
DATE
0
1
3/11
Initial release
Corrected ESD protection value; added “S” and “R” type specifications
—
11/11
1, 2, 3, 8, 12
Corrected the thermocouple temperature conditions in the Thermal Characteristics
table and Table 1; added clarification to the Serial Interface section to help users
better understand how to communicate with the device; added a recommendation to
add a 10nF differential capacitor to the T+/T- pins in the Noise Considerations section
2
2/12
3, 8, 9, 11
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. 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 Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
13
©
2012 Maxim Integrated Products
Maxim is a registered trademarꢀ of Maxim Integrated Products, Inc.
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