MAX31855_V01 [MAXIM]
Cold-Junction Compensated Thermocouple-to-Digital Converter;
| 型号： | MAX31855_V01 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Cold-Junction Compensated Thermocouple-to-Digital Converter |
| 文件： | 总13页 (文件大小：568K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
General Description
Benefits and Features
● Integration Reduces Design Time and Lowers
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 0.25°C, allows readings as
high as +1800°C and as low as -270°C, and exhibits
thermocouple accuracy of ±2°C for temperatures ranging
from -200°C to +700°C for K-type thermocouples. For full
range accuracies and other thermocouple types, see the
Thermal Characteristics specifications.
System Cost
• 14-Bit, 0.25°C Resolution Converter
• Integrated Cold-Junction Compensation
• Versions Available for Most Common Thermocouple
Types: K-, J-, N-, T-, S-, R-, and E-Type
• Detects Thermocouple Shorts to GND or V
• Detects Open Thermocouple
CC
● Interfaces to Most Microcontrollers
Applications
• Simple SPI-Compatible Interface (Read-Only)
● Industrial
● Appliances
● HVAC
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part, refer
to www.maximintegrated.com/MAX31855.related.
Typical Application Circuit
V
CC
0.1µF
MAX31855
GND
MICROCONTROLLER
SO
MISO
SCK
SS
SCK
T+
T-
CS
19-5793; Rev 5; 1/15
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......................... -40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range ........................... -65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
Soldering Temperature (reflow) ......................................+260°C
CC
All Other Pins............................................. -0.3V to (V
+ 0.3V)
CC
Continuous Power Dissipation (T = +70°C)
A
SO (derate 5.9mW/°C above +70°C).......................470.6mW
ESD Protection (All Pins, Human Body Model)....................±2kV
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.
(Note 1)
Package Thermal Characteristics
SO
Junction-to-Ambient Thermal Resistance (θ ) ........170°C/W
JA
Junction-to-Case Thermal Resistance (θ )...............40°C/W
JC
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
Recommended Operating Conditions
(T = -40°C to +125°C, 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 ≤ V
P 3.6V, T = -40°C to +125°C, unless otherwise noted.)
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Power-Supply Current
I
900
1500
µA
CC
T
= -40°C to +125°C, 100mV across the
A
Thermocouple Input Bias Current
Power-Supply Rejection
-100
+100
2.5
nA
°C/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
OUT
V
0.4
OL
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Thermal Characteristics
(3.0V ≤ V
P 3.6V, T = -40°C to +125°C, unless otherwise noted.) (Note 4)
CC
A
PARAMETER
SYMBOL
CONDITIONS
= -200°C to +700°C,
MIN
TYP
MAX
UNITS
T
T
THERMOCOUPLE
-2
+2
= -20°C to +85°C (Note 3)
A
MAX31855K Thermocouple
Temperature Gain and Offset
Error (41.276µV/°C nominal
sensitivity) (Note 4)
T
T
= +700°C to +1350°C,
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
°C
= -20°C to +85°C (Note 3)
A
T
T
= -270°C to +1372°C,
THERMOCOUPLE
= -40°C to +125°C (Note 3)
A
T
T
= -210°C to +750°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
MAX31855J Thermocouple
Temperature Gain and Offset
Error (57.953µV/°C nominal
sensitivity) (Note 4)
A
°C
°C
°C
°C
T
T
= -210°C to +1200°C,
THERMOCOUPLE
= -40°C to +125°C (Note 3)
A
T
T
= -200°C to +700°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
A
MAX31855N Thermocouple
Temperature Gain and Offset
Error (36.256µV/°C nominal
sensitivity) (Note 4)
T
T
= +700°C to +1300°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
A
T
T
= -270°C to +1300°C,
THERMOCOUPLE
= -40°C to +125°C (Note 3)
A
T
T
= -270°C to +400°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
MAX31855T Thermocouple
Temperature Gain and Offset
Error (52.18µV/°C nominal
sensitivity) (Note 4)
A
T
T
= -270°C to +400°C,
THERMOCOUPLE
= -40°C to +125°C (Note 3)
A
T
T
= -200°C to +700°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
A
MAX31855E Thermocouple
Temperature Gain and Offset
Error (76.373µV/°C nominal
sensitivity) (Note 4)
T
T
= +700°C to +1000°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
A
T
T
= -270°C to +1000°C,
THERMOCOUPLE
= -40°C to +125°C (Note 3)
A
T
T
= -50°C to +700°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
A
MAX31855R Thermocouple
Temperature Gain and Offset
Error (10.506µV/°C nominal
sensitivity) (Note 4)
T
T
= +700°C to +1768°C,
THERMOCOUPLE
°C
°C
= -20°C to +85°C (Note 3)
A
T
T
= -50°C to +1768°C,
THERMOCOUPLE
= -40°C to +125°C (Note 3)
A
T
T
= -50°C to +700°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
A
MAX31855S Thermocouple
Temperature Gain and Offset
Error (9.587µV/°C nominal
sensitivity) (Note 4)
T
T
= +700°C to +1768°C,
THERMOCOUPLE
= -20°C to +85°C (Note 3)
A
T
T
= -50°C to +1768°C,
THERMOCOUPLE
= -40°C to +125°C (Note 3)
A
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Thermal Characteristics (continued)
(3.0V ≤ V
P 3.6V, T = -40°C to +125°C, unless otherwise noted.) (Note 4)
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Thermocouple Temperature Data
Resolution
0.25
°C
T = -20°C to +85°C (Note 3)
A
-2
-3
+2
+3
Internal Cold-Junction
Temperature Error
°C
°C
T = -40°C to +125°C (Note 3)
A
Cold-Junction Temperature Data
Resolution
T = -40°C to +125°C
A
0.0625
70
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 Leakage Current
Input Capacitance
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
µA
pF
I
(Note 7)
-1
+1
LEAK
C
8
IN
Serial-Clock 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 = +25°C. 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
CC
CONV_PU
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
D0
SO
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
= +3.3V, T = +25°C, unless otherwise noted.)
A
CC
INTERNAL TEMPERATURE SENSOR
ACCURACY
SUPPLY CURRENT vs. TEMPERATURE
0.7
1.4
V
CC
= 3.3V
0.6
0.5
0.4
0.3
0.2
0.1
0
V
= 3.6V
CC
1.2
1.0
0.8
0.6
0.4
0.2
0
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
-40 -20
0
20 40 60 80 100 120
TEMPERATURE (°C)
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
CC
= 3.3V
INTERNAL TEMPERATURE = +25°C
20 40
ADC INPUT VOLTAGE (mV)
0
20
40
60
0
60
ADC INPUT VOLTAGE (mV)
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Pin Configuration
Pin Description
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
MAX31855
V
CC
T+
CS
SCK
Serial-Clock Input
V
CC
SCK
Active-Low Chip Select. Set CS low to
enable the serial interface.
6
CS
SO
7
8
SO
Serial-Data Output
Do Not Connect
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 coldjunction
side (device ambient temperature) and a 0°C virtual ref-
erence. For a K-type thermocouple, the voltage changes
by about 41µV/°C, which approximates the thermocouple
characteristic with the following linear equation:
Detailed Description
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 compensa-
tion sensing and correction, a digital controller, an SPI-
compatible interface, and associated control logic. The
device is designed to work in conjunction with an external
microcontroller (µC) in thermostatic, process-control, or
monitoring applications. The device is available in several
versions, each optimized and trimmed for a specific thermo-
couple 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
= (41.276µV/°C) x (T - T
)
AMB
OUT
R
where V
is the thermocouple output voltage (µV), T
R
OUT
is the temperature of the remote thermocouple junction
(°C), and T is the temperature of the device (°C).
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 con-
vert the thermocouple’s signal into a voltage compatible
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 the
Before converting the thermoelectric voltages into equiva-
lent temperature values, it is necessary to compensate
Table 1. Thermocouple Wire Connections and Nominal Sensitivities
COLD-JUNCTION
SENSITIVITY (µV/°C)
(0°C TO +70°C)
TYPE
T- WIRE
T+ WIRE
TEMP RANGE (°C)
SENSITIVITY (µV/°C)
41.276
(0°C to +1000°C)
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
(0°C to +750°C)
36.256
(0°C to +1000°C)
N
S
T
E
R
Nicrosil
9.587
(0°C to +1000°C)
Platinum
Constantan
Constantan
Platinum
Platinum/Rhodium
Copper
52.18
(0°C to +400°C)
41.56
76.373
(0°C to +1000°C)
Chromel
44.123
6.158
10.506
(0°C to +1000°C)
Platinum/Rhodium
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
same temperature as the board on which the device is
mounted) can range from -55°C to +125°C. While the
temperature at the cold end fluctuates, the device contin-
ues to accurately sense the temperature difference at the
opposite end.
During fault detection, the connections from the external
thermocouple and cold-junction compensation circuit 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 circuit are
closed (switch S1 and S2). The fault-detection circuit tests
The device senses and corrects for the changes in the
reference junction temperature with cold-junction com-
pensation. 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.
for shorted connections to V
or GND on the T+ and T-
CC
inputs, as well as looking for an open thermocouple condi-
tion. Bits D0, D1, and D2 of the output data are normally
low. Bit D2 goes high to indicate a thermocouple short to
V
, bit D1 goes high to indicate a thermocouple short
CC
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
The Typical Application Circuit shows the device inter-
faced with a microcontroller. In this example, the device
processes the reading from the thermocouple and trans-
mits the data through a serial interface. Drive CS low
and apply a clock signal at SCK to read the results at
SO. Conversions are always being performed in the
background. The fault and temperature data are only be
updated when CS is high.
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.
Conversion Functions
During the conversion time, t
, three functions are
CONV
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 com-
plete serial-interface read of the cold-junction compen-
sated thermocouple temperature requires 14 clock cycles.
Thirty-two clock cycles are required to read both the
thermocouple and reference junction temperatures (Table
2 and Table 3.) The first bit, D31, is the thermocouple
temperature sign bit, and is presented to the SO pin within
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).
t
of the falling edge of CS. Bits D[30:18] contain the
DV
converted temperature in the order of MSB to LSB, and
are presented to the SO pin within t of the falling edge
D0
of SCK. Bit D16 is normally low and goes high when the
thermocouple input is open or shorted to GND or V
.
CC
The reference junction temperature data begins with D15.
CS can be taken high at any point while clocking out con-
version data. If T+ and T- are unconnected, the thermo-
couple temperature sign bit (D31) is 0, and the remainder
of the thermocouple temperature value (D[30:18]) is 1.
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.
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
SCV
BIT
SCG
BIT
OC
BIT
RES
RES
DATA
BIT
D31
Sign
D30
…
…
D18
D17
D16
D15
Sign
D14
…
…
D4
D3
D2
D1
D0
1 =
Short
to
1 =
Short
to
MSB
1 =
Open
Circuit
10
-2
-4
MSB 2
(1024°C)
LSB 2
(0.25°C)
1 =
Fault
LSB 2
(0.0625°C)
6
VALUE
Reserved
2
Reserved
(64°C)
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.
Reserved
This bit always reads 0.
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
(°C)
DIGITAL OUTPUT
(D[31:18])
TEMPERATURE
(°C)
DIGITAL OUTPUT
(D[15:4])
+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 thermo-
couple type.
Maxim Integrated
│ 10
www.maximintegrated.com
MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
The thermocouple system’s accuracy can also be
improved by following these precautions:
Applications Information
Noise Considerations
•
Use the largest wire possible that does not shunt heat
away from the measurement area.
Because of the small signal levels involved, thermocouple
temperature measurement is susceptible to powersupply
coupled noise. The effects of power-supply noise can be
minimized by placing a 0.1µF ceramic bypass capacitor
•
If a small wire is required, use it only in the region
of the measurement, and use extension wire for the
region with no temperature gradient.
close to the V
pin of the device and to GND.
CC
•
•
Avoid mechanical stress and vibration, which could
strain the wires.
The input amplifier is a low-noise amplifier designed
to enable high-precision input sensing. Keep the ther-
mocouple 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.
When using long thermocouple wires, use a twisted
pair extension wire.
•
•
Avoid steep temperature gradients.
Try to use the thermocouple wire well within its tem-
perature rating.
Thermal Considerations
•
•
•
Use the proper sheathing material in hostile environ-
ments to protect the thermocouple wire.
Self-heating degrades the device’s temperature measure-
ment accuracy in some applications. The magnitude of
the temperature errors depends on the thermal conduc-
tivity of the device package, the mounting technique, and
the effects of airflow. Use a large ground plane to improve
the device’s temperature measurement accuracy.
Use extension wire only at low temperatures and only
in regions of small gradients.
Keep an event log and a continuous record of thermo-
couple resistance.
Maxim Integrated
│ 11
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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
PIN-PACKAGE
8 SO
K
K
J
-200°C to +1350°C
-200°C to +1350°C
-40°C to +750°C
-40°C to +750°C
-200°C to + 1300°C
-200°C to + 1300°C
-50°C to +1600°C
-50°C to +1600°C
-250°C to +400°C
-250°C to +400°C
-40°C to +900°C
-40°C to +900°C
-50°C to +1770°C
-50°C to +1770°C
8 SO
8 SO
J
8 SO
N
N
S
S
T
T
E
E
R
R
8 SO
8 SO
8 SO
8 SO
8 SO
8 SO
8 SO
8 SO
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 package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
OUTLINE NO.
LAND PATTERN NO.
8 SO
S8+4
21-0041
90-0096
Maxim Integrated
│ 12
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MAX31855
Cold-Junction Compensated
Thermocouple-to-Digital Converter
Revision History
REVISION REVISION
PAGES
CHANGED
DESCRIPTION
NUMBER
DATE
0
1
3/11
Initial release
—
11/11
Corrected ESD protection value; added “S” and “R” type specifications
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
Change “S” type thermocouple minimum temperature in Table 1 and Ordering
Information
3
7/14
8, 12
4
5
11/14
1/15
Removed automotive reference from data sheet
1
1
Revised Benefits and Features section
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated 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 and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
2015 Maxim Integrated Products, Inc.
│ 13
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