MAX6674ISA+ Maxim Integrated Products, MAX6674ISA+ Datasheet - Page 5

• Manufacturer Part Number: MAX6674ISA+
• Description: IC THERMOCOUP TO DGTL 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Temperature Sensorr

Specifications of MAX6674ISA+

• Input Type: Logic
• Output Type: Logic
• Interface: 3-Wire SPI Serial
• Current - Supply: 2mA
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Full Temp Accuracy: +/- 2 C
• Digital Output - Bus Interface: 3-Wire, SPI
• Digital Output - Number Of Bits: 10 bit
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 3 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 20 C
• Supply Current: 2 mA
• Sensing Accuracy Range: ± 2°C
• Supply Voltage Range: 3V To 5.5V
• Resolution (bits): 10bit
• Sensor Case Style: SOIC
• No. Of Pins: 8
• Operating Temperature Range: -20°C To +85°C
• Rohs Compliant: Yes
• Data Interface: 2-Wire, I2C, Serial
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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.
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.
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.
Cold-Junction-Compensated K-Thermocouple-
Applications Information
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Noise Considerations
Open Thermocouple
to-Digital Converter (0°C to +128°C)
Serial Interface
Self-heating degrades the temperature measurement
accuracy of the MAX6674 in some applications. The
magnitude of the temperature errors depends on the
thermal conductivity of the MAX6674 package, the
mounting technique, and the effects of airflow. Use a
large ground plane to improve the temperature mea-
surement accuracy.
The accuracy of a thermocouple system can also be
improved by following these precautions:
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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.
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 envi-
ronments 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
Thermal Considerations
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