MAXIM MAX6674 User Manual

General Description

The MAX6674 cold-junction-compensation thermocou­ple-to-digital converter performs cold-junction compen­sation 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

Automotive

Features

♦ Cold-Junction Compensation

♦ Simple SPI-Compatible Serial Interface

♦ 10 Bit, 0.125°C

♦ Open Thermocouple Detection

MAX6674

Cold-Junction-Compensated K-Thermocouple-

to-Digital Converter (0°C to +128°C)

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

Vcc

GND

T+

T-

SO

SCK

CS

MICROCONTROLLER

68HC11A8

MISO

SCK

SSB

0.1µF

MAX6674

Typical Application Circuit

19-2241; Rev 1; 8/02

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.

Ordering Information

SPI is a trademark of Motorola, Inc.

PART TEMP RANGE PIN-PACKAGE

MAX6674ISA -20°C to +85°C 8 SO

TOP VIEW

GND

1

2

MAX6674

3

T+

4

CC

87N.C.

SOT-

CS

6

SCKV

5

SO

MAX6674

Cold-Junction-Compensated K-Thermocouple­to-Digital Converter (0°C to +128°C)

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +3.0V to +5.5V, TA= -20°C to +85°C, unless otherwise noted. Typical values specified at +25°C.) (Note 1)

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.

Supply Voltage (VCCto GND) ................................. -0.3V to +6V

SO, SCK, CS, T-, T+ to GND .......................-0.3V to V

CC

+ 0.3V

SO Current .........................................................................50mA

ESD Protection (Human Body Model) ........................... ±2000V

Continuous Power Dissipation (T

A

= +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 Package

Vapor Phase (60s) ......................................................+215°C

Infrared (15s) ..............................................................+220°C

Lead Temperature (soldering, 10s) ................................ +300°C

Temperature Error

Temperature Conversion
Constant

Cold-Junction Compensation

Resolution 0.125 °C

Thermocouple Input Impedance 20 kΩ

Supply Voltage V

Supply Current I

Power-On Reset Threshold VCC rising 1 2 2.5 V

Power-On Reset Hysteresis 50 mV

Conversion Time (Note 2) 0.15 0.18 s

SERIAL INTERFACE

Input Low Voltage V

Input High Voltage V

Input Leakage Current I

Input Capacitance C

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

T

THERMOCOUPLE

+100°C, T
(Note 2)

T

THERMOCOUPLE

0°C to +125°C, T
+25°C (Note 2)

= +25°C

A

=

VCC = +3.3V -1 +1

V

= +5V -1.5 +1.5

CC

=

VCC = +3.3V -2 +2

=

A

V

= +5V -3 +3

CC

5.125 µv/LSB

CC

CC

IL

IH

LEAK

IN

TA = +25°CV

= -20°C to +85°C

T

A

(Note 2)

VIN = GND or V

CC

= +3.3V -1 +1

CC

= +3.3V and +5V -3 +3

V

CC

3.0 5.5 V

12mA

0.7 x
V

CC

-5 5 µA

5pF

0.3 x
V

CC

°C

°C

V

V

MAX6674

Cold-Junction-Compensated K-Thermocouple-

to-Digital Converter (0°C to +128°C)

_______________________________________________________________________________________ 3

Typical Operating Characteristics

(VCC= +3.3V, TA= +25°C, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +3.0V to +5.5V, TA= -20°C to +85°C, unless otherwise noted. Typical values specified at +25°C.) (Note 1)

Note 1: All specifications are 100% tested at T

A

= +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.

Output High Voltage V

Output Low Voltage V

TIMING

Serial Clock Frequency f

SCK Pulse High Width t

SCK Pulse Low Width t

CSB Fall to SCK Rise t

CSB Fall to Output Enable t

CSB Rise to Output Disable t

SCK Fall to Output Data Valid t

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

V

-

OH

OL

SCL

CH

CL

CSS

DV

TR

DO

I

I

= 1.6mA

SOURCE

= 1.6mA 0.4 V

SINK

CL = 10pF 100 ns

CL = 10pF 100 ns

CL = 10pF 100 ns

CL = 10pF 100 ns

CC

0.4

100 ns

100 ns

V

4.3 MHz

OUTPUT CODE ERROR

vs. TEMPERATURE

2

1

0

OUTPUT CODE ERROR (°C)

-1

-2
04515 30 60 75 90

TEMPERATURE (°C)

MAX6674 toc01

OUTPUT CODE ERROR

vs. VOLTAGE DIFFERENTIAL

2

1

0

OUTPUT CODE ERROR (°C)

-1

-2

-1200 12000 2400 3600 4800
VOLTAGE DIFFERENTIAL (µV)

MAX6674 toc02