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PDF MAX6674 Data sheet ( Hoja de datos )
| Número de pieza | MAX6674 | |
| Descripción | Cold-Junction-Compensated K-Thermocouple to-Digital Converter (0C to +128C) | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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19-2241; Rev 1; 8/02
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 compen-
sation 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.
o Cold-Junction Compensation
Features
o Simple SPI-Compatible Serial Interface
o 10 Bit, 0.125°C
o Open Thermocouple Detection
PART
MAX6674ISA
Ordering Information
TEMP RANGE
-20°C to +85°C
PIN-PACKAGE
8 SO
Industrial
Appliances
HVAC
Automotive
Applications
SPI is a trademark of Motorola, Inc.
TOP VIEW
Pin Configuration
GND 1
T- 2
T+ 3
VCC 4
MAX6674
8 N.C.
7 SO
6 CS
5 SCK
SO
0.1µF
Vcc
MAX6674
GND
SO
T+ SCK
T- CS
Typical Application Circuit
MICROCONTROLLER
68HC11A8
MISO
SCK
SSB
________________________________________________________________ Maxim Integrated Products 1
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.
1 page  
Cold-Junction-Compensated K-Thermocouple-
to-Digital Converter (0°C to +128°C)
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
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:
• 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
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.
_______________________________________________________________________________________ 5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet MAX6674.PDF ] | |
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