Maxim MAX6675ISA, MAX6675 Datasheet

General Description

The MAX6675 performs cold-junction compensation
and digitizes the signal from a type-K thermocouple.
The data is output in a 12-bit resolution, SPI™-compati­ble, read-only format.

This converter resolves temperatures to 0.25°C, allows
readings as high as +1024°C, and exhibits thermocou­ple accuracy of 8LSBs for temperatures ranging from
0°C to +700°C.

The MAX6675 is available in a small, 8-pin SO package.

Applications

Industrial

Appliances

HVAC

Automotive

Features

♦ Direct Digital Conversion of Type -K

Thermocouple Output

♦ Cold-Junction Compensation

♦ Simple SPI-Compatible Serial Interface

♦ 12-Bit, 0.25°C Resolution

♦ Open Thermocouple Detection

MAX6675

Cold-Junction-Compensated K-Thermocouple-

to-Digital Converter (0°C to +1024°C)

________________________________________________________________ Maxim Integrated Products 1

CS

SCKV

CC

1

2

87N.C.

SOT-

T+

GND

SO

TOP VIEW

3

4

6

5

MAX6675

Pin Configuration

Vcc

GND

T+

T-

SO

SCK

CS

MICROCONTROLLER

68HC11A8

MISO

SCK

SSB

0.1µF

MAX6675

Typical Application Circuit

19-2235; Rev 1; 3/02

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

MAX6675ISA -20°C to +85°C 8 SO

MAX6675

Cold-Junction-Compensated K-Thermocouple­to-Digital Converter (0°C to +1024°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 VCC+ 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

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

VCC = +3.3V -5 +5

T

A

= +25°C (Note 2)

V

CC

= +5V -6 +6

VCC = +3.3V -8 +8

T

THERMOCOUPLE

= 0°C to

VCC = +5V -9 +9

VCC = +3.3V -17

Temperature Error

T

THERMOCOUPLE

= +700°C

to +1000°C, T

A

= +25°C

(Note 2)

V

CC

= +5V -19

LSB

Thermocouple Conversion
Constant

µV/LSB

VCC = +3.3V

Cold-Junction
Compensation Error

TA = -20°C to +85°C
(Note 2)

V

CC

= +5V

°C

Resolution

°C

Thermocouple Input
Impedance

60 kΩ

Supply Voltage V

CC

3.0 5.5 V

Supply Current I

CC

0.7 1.5 mA

Power-On Reset Threshold VCC rising 1 2 2.5 V

Power-On Reset Hysteresis 50 mV

Conversion Time (Note 2)

s

SERIAL INTERFACE

Input Low Voltage V

IL

0.3 x
V

Input High Voltage V

IH

0.7 x
V

Input Leakage Current I

LEAK

VIN = GND or V

CC

±5µA

Input Capacitance C

IN

5pF

T

THERMOCOUPLE

+700°C, T

= +700°C,

= +25°C (Note 2)

A

10.25

-3.0 +3.0

-3.0 +3.0

0.25

0.17 0.22

V

CC

+17

+19

V

CC

MAX6675

Cold-Junction-Compensated K-Thermocouple-

to-Digital Converter (0°C to +1024°C)

_______________________________________________________________________________________ 3

10

8

6

4

2

0

04515 30 60 75 90

OUTPUT CODE ERROR

vs. AMBIENT TEMPERATURE

MAX6675 toc01

TEMPERATURE (°C)

OUTPUT CODE ERROR (LSB)

-5

0

5

10

-10 0 30 50

OUTPUT CODE ERROR

vs. VOLTAGE DIFFERENTIAL

MAX6675 toc02

VOLTAGE DIFFERENTIAL (mV)

OUTPUT CODE ERROR (LSB)

10 20 40

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= T

MIN

to T

MAX

) are guaranteed

by design and characterization, not production tested.

Note 2: Guaranteed by design. Not production tested.

PARAMETER

CONDITIONS

UNITS

Output High Voltage V

OH

I

SOURCE

= 1.6mA

V

CC

-

0.4

V

Output Low Voltage V

OL

I

SINK

= 1.6mA 0.4 V

TIMING

Serial Clock Frequency f

SCL

4.3

MHz

SCK Pulse High Width t

CH

ns

SCK Pulse Low Width t

CL

ns

CSB Fall to SCK Rise t

CSS

CL = 10pF

ns

CSB Fall to Output Enable t

DV

CL = 10pF 100 ns

CSB Rise to Output Disable t

TR

CL = 10pF 100 ns

SCK Fall to Output Data
Valid

t

DO

CL = 10pF 100 ns

SYMBOL

MIN TYP MAX

100

100

100