MAX6674ISA+-MAX6674ISA+T Fast Delivery |IC PHOENIX CO.,LIMITED

MAX6674ISA+ ,Cold-Junction-Compensated K-Thermocouple-to-Digital Converter (0°C to +128°C)Electrical Characteristics(V = +3.0V to +5.5V, T = -20°C to +85°C, unless otherwise noted. Typical ..
MAX6674ISA+T ,Cold-Junction-Compensated K-Thermocouple-to-Digital Converter (0°C to +128°C)FeaturesThe MAX6674 cold-junction-compensation thermocou-● Cold-Junction Compensationple-to-digital ..
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MAX6675ISA+T ,Cold-Junction-Compensated K-Thermocouple-to-Digital Converter (0°C to +1024°C)Electrical Characteristics(V = +3.0V to +5.5V, T = -20°C to +85°C, unless otherwise noted. Typical ..
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MAX6674ISA+-MAX6674ISA+T
Cold-Junction-Compensated K-Thermocouple-to-Digital Converter (0°C to +128°C)
General Description
The MAX6674 cold-junction-compensation thermocou-
ple-to-digital converter performs cold-junction compensa-
tion and digitizes the signal from a type-K thermocouple.
The data is output in a 10-bit resolution, SPI™-compatible,
read-only format.
This converter resolves temperatures to 0.125°C, allows
readings as high as +128°C, and exhibits thermocouple
accuracy of ±2°C for temperatures ranging from 0°C to
+125°C.
The MAX6674 is available in a small, 8-pin SO package.
Applications●Industrial●Appliances●HVAC
Features●Cold-Junction Compensation●Simple SPI-Compatible Serial Interface●10 Bit, 0.125°C●Open Thermocouple Detection
PARTTEMP RANGEPIN-PACKAGE
MAX6674ISA-20°C to +85°C8 SO
Vcc
GND
SCK
MICROCONTROLLER
68HC11A8
MISO
SCK
SSB
0.1µF
MAX6674
SCKVCC
N.C.T-
GND
TOP VIEW
MAX6674
MAX6674Cold-Junction-Compensated K-Thermocouple-
to-Digital Converter (0°C to +128°C)
Typical Application Circuit
Pin Coniguration
Ordering Information
Supply Voltage (VCC to GND) ................................ -0.3V to +6V
SO, SCK, CS, T-, T+ to GND .....................-0.3V to VCC + 0.3V
SO Current ........................................................................50mA
ESD Protection (Human Body Model) .......................... ±2000V
Continuous Power Dissipation (TA = +70°C) 8-Pin SO (derate 5.88mW/°C above +70°C) ...............471mW
Operating Temperature Range ...........................-20°C to +85°C
Storage Temperature Range ............................-65°C to +150°C
Junction Temperature ......................................................+150°C
SO PackageVapor Phase (60s) ......................................................+215°CInfrared (15s) ..............................................................+220°C
Lead Temperature (soldering, 10s) ................................ +300°C
(VCC = +3.0V to +5.5V, TA = -20°C to +85°C, unless otherwise noted. Typical values specified at +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
Temperature Error
TTHERMOCOUPLE =
+100°C, TA = +25°C
(Note 2)
VCC = +3.3V-1+1
VCC = +5V-1.5+1.5
TTHERMOCOUPLE =
0°C to +125°C, TA =
+25°C (Note 2)
VCC = +3.3V-2+2
VCC = +5V-3+3
Temperature Conversion
Constant5.125µv/LSB
Cold-Junction Compensation
TA = +25°CVCC = +3.3V-1+1TA = -20°C to +85°C
(Note 2)
VCC = +3.3V and
+5V-3+3
Resolution0.125°C
Thermocouple Input Impedance20kΩ
Supply VoltageVCC3.05.5V
Supply CurrentICC12mA
Power-On Reset ThresholdVCC rising122.5V
Power-On Reset Hysteresis50mV
Conversion Time(Note 2)0.150.18s
SERIAL INTERFACE
Input Low VoltageVIL0.3 x
VCCV
Input High VoltageVIH0.7 x
VCCV
Input Leakage CurrentILEAKVIN = GND or VCC-55µA
Input CapacitanceCIN5pF
MAX6674Cold-Junction-Compensated K-Thermocouple-
to-Digital Converter (0°C to +128°C)
Electrical Characteristics
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.
Absolute Maximum Ratings
Note 1: All specifications are 100% tested at TA = +25°C. Specification limits over temperature (TA = -20°C to +85°C) are guaran-
teed by design and characterization, not production tested.
Note 2: Guaranteed by design. Not production tested.
(VCC = +3.3V, TA = +25°C, unless otherwise noted.)
(VCC = +3.0V to +5.5V, TA = -20°C to +85°C, unless otherwise noted. Typical values specified at +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
Output High VoltageVOHISOURCE = 1.6mAVCC -
0.4V
Output Low VoltageVOLISINK = 1.6mA0.4V
TIMING
Serial Clock FrequencyfSCL4.3MHz
SCK Pulse High WidthtCH100ns
SCK Pulse Low WidthtCL100ns
CSB Fall to SCK RisetCSSCL = 10pF100ns
CSB Fall to Output EnabletDVCL = 10pF100ns
CSB Rise to Output DisabletTRCL = 10pF100ns
SCK Fall to Output Data ValidtDOCL = 10pF100ns
OUTPUT CODE ERROR
vs. VOLTAGE DIFFERENTIAL
MAX6674 toc02
VOLTAGE DIFFERENTIAL (µV)
OUTPUT CODE ERROR (451530607590
OUTPUT CODE ERROR
vs. TEMPERATURE
MAX6674 toc01
TEMPERATURE (°C)
OUTPUT CODE ERROR (
MAX6674Cold-Junction-Compensated K-Thermocouple-
to-Digital Converter (0°C to +128°C)
Typical Operating Characteristics
Electrical Characteristics (continued)
Detailed Description
The MAX6674 is a sophisticated thermocouple-to-digi-
tal converter with a built-in 10-bit analog-to-digital con-
verter (ADC). The device also contains cold-junction
compensation sensing and correction, a digital con-
troller, an SPI-compatible interface, and associated
control logic.
The MAX6674 is designed to work in conjunction with
an external microcontroller (µC) or other intelligence
in thermostatic, process-control, or monitoring applica-
tions. The µC is typically a power-management or key-
board controller, generating SPI serial commands by
“bit-banging” general-purpose input-output (GPIO) pins
or through a dedicated SPI interface block.
Temperature Conversion
The MAX6674 includes signal conditioning hardware to
convert the thermocouple’s signal into a voltage that is
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.
Before converting the thermoelectric voltages into
equivalent temperature values, it is necessary to com-
pensate for the difference between the thermocouple
cold-junction side (MAX6674 ambient temperature) and
a 0°C virtual reference.
For a type-K thermocouple, the voltage changes by
41µV/°C, which approximates the thermocouple charac-
teristic with the following linear equation:
VOUT = (41µV/°C) 5 (TR - TAMB)
where:
VOUT is the thermocouple output voltage (µV).
TR is the temperature of the remote point (°C).
TAMB is the ambient temperature (°C).
Cold-Junction Compensation
The function of the thermocouple is to sense a difference
in temperature between two ends. The thermocouple’s
hot junction can be read from 0°C to +127.875°C. The
cold end (ambient temperature of the board on which
the MAX6674 is mounted) can only range from -20°C to
+85°C. While the temperature at the cold end fluctuates,
the MAX6674 continues to accurately sense the tempera-
ture difference at the opposite end.
The MAX6674 senses and corrects for the changes in
the ambient temperature with cold-junction compensa-
tion. The device converts the ambient temperature
reading into a voltage using a temperature-sensing
diode. To make the actual thermocouple temperature
measurement, the MAX6674 measures the voltage from
the thermocouple’s output and from the sensing diode.
The device’s internal circuitry passes the diode’s volt-
age (sensing ambient temperature) and thermocouple
voltage (sensing remote temperature minus ambient
temperature) to the conversion function stored in the
ADC to calculate the thermocouple’s hot-junction tem-
perature.
Optimal performance from the MAX6674 is achieved
when the thermocouple cold junction and the device
are at the same temperature. Avoid placing heat-gener-
ating devices or components near the MAX6674
because this may produce cold-junction-related errors.
Digitization
The ADC adds the cold-junction diode measurement
with the amplified thermocouple voltage and reads out
the 10-bit sequence onto the S0 pin. A sequence of
all zeros means the thermocouple reading is 0°C. A
sequence of all ones means the thermocouple reading is
+127.875°C.
PINNAMEFUNCTIONGNDGroundT-
Alumel Lead of Type-K Thermocouple.
Should be connected to ground
externally.T+Chromel Lead of Type-K ThermocoupleVCCPositive Supply. Bypass with a 0.1µF
capacitor to GND.SCKSerial Clock InputCSChip Select. Set CS low to enable the
serial interface.S0Serial Data OutputN.C.No Connection
MAX6674Cold-Junction-Compensated K-Thermocouple-
to-Digital Converter (0°C to +128°C)
Pin Description
Applications Information
Serial Interface
The Typical Application Circuit shows the MAX6674
interfaced with a microcontroller. In this example, the
MAX6674 processes the reading from the thermocou-
ple and transmits the data through a serial interface.
Force CS low and apply a clock signal at SCK to read
the results at S0. Forcing CS low immediately stops any
conversion process. Initiate a new conversion process
by forcing CS high.
Force CS low to output the first bit on the S0 pin. A
complete serial interface read requires 16 clock cycles.
Read the 16 output bits on the falling edge of the clock.
The first bit, D15, is a dummy sign bit and always zero.
Bits D14–D5 contain the converted temperature in the
order of MSB to LSB. Bit D4 reads a high value when
any of the thermocouple inputs are open. Bit D3 is
always low to provide a device ID for the MAX6674.
Bits D2–D0 are in three-state when CS is high.
Figure 1a is the serial interface protocol and Figure 1b
shows the serial interface timing. Figure 2 is the S0 output.
Open Thermocouple
Bit D4 is normally low and goes high if the thermocou-
ple input is open. The open thermocouple detection cir-
cuit is implemented completely into the MAX6674. In
order to allow the operation of the open thermocouple
detector, T- must be grounded. Make the ground con-
nection as close to the GND pin as possible.
Noise Considerations
The accuracy of the MAX6674 is susceptible to power-
supply coupled noise. The effects of power-supply
noise can be minimized by placing a 0.1µF ceramic
bypass capacitor close to the supply pin of the device.
Thermal Considerations
Self-heating degrades the temperature measurement
accuracy of the MAX6674 in some applications. The
magnitude of the temperature errors depends on the ther-
mal conductivity of the MAX6674 package, the mounting
technique, and the effects of airflow. Use a large ground
plane to improve the temperature measurement accuracy.
The accuracy of a thermocouple system can also be
improved by following these precautions:●Use the largest wire possible that does not shunt
heat away from the measurement area.●If small wire is required, use it only in the region of
the measurement and use extension wire for the
region with no temperature gradient.●Avoid mechanical stress and vibration that could
strain the wires.●When using long thermocouple wires, use a twist-
ed-pair extension wire.●Avoid steep temperature gradients.●Try to use the thermocouple wire well within its tem-
perature rating.●Use the proper sheathing material in hostile environ-
ments to protect the thermocouple wire.●Use extension wire only at low temperatures and
only in regions of small gradients.●Keep an event log and a continuous record of ther-
mocouple resistance.
Reducing Effects of Pick-Up Noise
The input amplifier (A1) is a low-noise amplifier
designed to enable high-precision input sensing. Keep
the thermocouple and connecting wires away from
electrical noise sources.
MAX6674Cold-Junction-Compensated K-Thermocouple-
to-Digital Converter (0°C to +128°C)
Figure 2. S0 Output
Figure 1b. Serial Interface Timing
Figure 1a. Serial Interface Protocol
BITDUMMY
SIGN BIT
10-BIT
TEMPERATURE READING
THERMOCOUPLE
INPUT
DEVICESTATE
Bit1514131211109876543210MSBLSB0Three-state
D15D0D1D2D3
SCK
tDV
tCSS
tDO
tTR
tCHtCL
SCK
D15D14D13D12D11D10D9D8D7D6D5D4D3D1D0
MAX6674Cold-Junction-Compensated K-Thermocouple-
to-Digital Converter (0°C to +128°C)

Partno	Mfg	Dc	Qty	Available	Descript
MAX6674ISA+ \|MAX6674ISA	MAXIM	N/a	910	avai	Cold-Junction-Compensated K-Thermocouple-to-Digital Converter (0°C to +128°C)
MAX6674ISA+T \|MAX6674ISAT	MAXIM	N/a	817	avai	Cold-Junction-Compensated K-Thermocouple-to-Digital Converter (0°C to +128°C)