AD8497 AD [Analog Devices], AD8497 Datasheet

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AD8497

Manufacturer Part Number
AD8497
Description
Precision Thermocouple Amplifiers with Cold Junction Compensation
Manufacturer
AD [Analog Devices]
Datasheet

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FEATURES
Low cost and easy to use
Pretrimmed for J or K type thermocouples
Internal cold junction compensation
High impedance differential input
Standalone 5 mV/°C thermometer
Reference pin allows offset adjustment
Thermocouple break detection
Laser wafer trimmed to 1°C initial accuracy
Low power: <1 mW at V
Wide power supply range
Small, 8-lead MSOP
APPLICATIONS
J or K type thermocouple temperature measurement
Setpoint controller
Celsius thermometer
Universal cold junction compensator
White goods (oven, stove top) temperature measurements
Exhaust gas temperature sensing
Catalytic converter temperature sensing
GENERAL DESCRIPTION
The AD8494/AD8495/AD8496/AD8497 are precision instrumen-
tation amplifiers with thermocouple cold junction compensators
on an integrated circuit. They produce a high level (5 mV/°C)
output directly from a thermocouple signal by combining an
ice point reference with a precalibrated amplifier. They can be
used as standalone thermometers or as switched output setpoint
controllers using either a fixed or remote setpoint control.
The AD8494/AD8495/AD8496/AD8497 can be powered from a
single-ended supply (less than 3 V) and can measure temperatures
below 0°C by offsetting the reference input. To minimize self-
heating, an unloaded AD849x typically operates with a total
supply current of 180 μA, but it is also capable of delivering in
excess of ±5 mA to a load.
The AD8494 and AD8496 are precalibrated by laser wafer
trimming to match the characteristics of J type (iron-constantan)
thermocouples; the AD8495 and AD8497 are laser trimmed to
match the characteristics of K type (chromel-alumel) thermo-
couples. See Table 1 for the optimized ambient temperature
range of each part.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
and 0.025°C/°C ambient temperature rejection
Single supply: 2.7 V to 36 V
Dual supply: ±2.7 V to ±18 V
S
= 5 V
Precision Thermocouple Amplifiers
with Cold Junction Compensation
AD8494/AD8495/AD8496/AD8497
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
Table 1. Device Temperature Ranges
Part No.
AD8494
AD8495
AD8496
AD8497
The AD8494/AD8495/AD8496/AD8497 allow a wide variety of
supply voltages. With a 5 V single supply, the 5 mV/°C output
allows the devices to cover nearly 1000 degrees of a thermo-
couple’s temperature range.
The AD8494/AD8495/AD8496/AD8497 work with 3 V supplies,
allowing them to interface directly to lower supply ADCs. They
can also work with supplies as large as 36 V in industrial systems
that require a wide common-mode input range.
PRODUCT HIGHLIGHTS
1.
2.
3.
4.
5.
6.
THERMO-
COUPLE
Complete, precision laser wafer trimmed thermocouple
signal conditioning system in a single IC package.
Flexible pinout provides for operation as a setpoint
controller or as a standalone Celsius thermometer.
Rugged inputs withstand 4 kV ESD and provide over-
voltage protection (OVP) up to V
Differential inputs reject common-mode noise on the
thermocouple leads.
Reference pin voltage can be offset to measure 0°C on
single supplies.
Available in a small, 8-lead MSOP that is fully RoHS compliant.
1MΩ
+IN
–IN
Thermo-
couple
Type
J
K
J
K
FUNCTIONAL BLOCK DIAGRAM
ESD AND
ESD AND
OVP
OVP
Ambient Temperature
(Reference Junction)
0°C to 50°C
0°C to 50°C
25°C to 100°C
25°C to 100°C
©2010 Analog Devices, Inc. All rights reserved.
A2
A1
Optimized Temperature Range
Figure 1.
AD8494/AD8495/
AD8496/AD8497
COLD JUNCTION
COMPENSATION
S
± 25 V.
SENSE
www.analog.com
REF
Measurement
Junction
Full J type range
Full K type range
Full J type range
Full K type range
A3
OUT

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AD8497 Summary of contents

Page 1

... The AD8494 and AD8496 are precalibrated by laser wafer trimming to match the characteristics of J type (iron-constantan) thermocouples; the AD8495 and AD8497 are laser trimmed to match the characteristics of K type (chromel-alumel) thermo- couples. See Table 1 for the optimized ambient temperature range of each part ...

Page 2

... Pin Configuration and Function Descriptions ............................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ...................................................................... 11 REVISION HISTORY 7/10—Revision 0: Initial Version   Thermocouples ........................................................................... 11   Thermocouple Signal Conditioner .......................................... 11   AD8494/AD8495/AD8496/AD8497 Architecture .................. 11   Maximum Error Calculation .................................................... 12   Recommendations for Best Circuit Performance .................. 13   Applications Information .............................................................. 14   Basic Connection ....................................................................... 14   ...

Page 3

... Output Voltage Range 5 Short-Circuit Current DYNAMIC RESPONSE −3 dB Bandwidth AD8494 AD8495/AD8497 AD8496 Settling Time to 0. output step AD8494 AD8495/AD8497 AD8496 POWER SUPPLY 6 Operating Voltage Range Single Supply Dual Supply Quiescent Current = 25° 100 kΩ, unless otherwise noted. Specifications do not include ...

Page 4

... With a 100 kΩ load, measurement junction temperatures beyond approximately 880°C for the AD8494 and AD8496 and beyond approximately 960°C for the AD8495 and AD8497 require supply voltages larger than negative voltage applied to the reference pin. Measurement junction temperatures below 5°C require either a positive offset voltage applied to the reference pin or a negative supply ...

Page 5

... JEDEC PCB in free air. Rating JA ±18 V Table 4. +V – Package – 8-Lead MSOP (RM-8) ±V S Indefinite −65°C to +150°C ESD CAUTION −40°C to +125°C 140°C 4.5 kV 1.5 kV Rev Page AD8494/AD8495/AD8496/AD8497 θ JA 135 Unit °C/W ...

Page 6

... AD8494/AD8495/AD8496/AD8497 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Table 5. Pin Function Descriptions Pin No. Mnemonic Description 1 −IN Negative Input. 2 REF Reference. This pin must be driven by low impedance. 3 −V Negative Supply Connect. 5 SENSE Sense Pin. In measurement mode, connect to output; in setpoint mode, connect to setpoint voltage. ...

Page 7

... Figure 7. Input Common-Mode Voltage Range vs. Output Voltage 100k 1M Figure 8. Input Bias Current and Input Offset Current vs. Temperature Rev Page AD8494/AD8495/AD8496/AD8497 1200 1000 CONNECTED THERMOCOUPLE 800 600 400 200 OPEN THERMOCOUPLE 0 THERMOCOUPLE CONNECTION AD849x OUTPUT –200 TIME (50µ ...

Page 8

... V (Gain = 96.7) Figure 12. AD8494 Input Overvoltage Performance 2. 1.50 8 1.00 4 0.50 0 –4 0 –8 –0.50 –12 –1.00 – –30 Figure 13. AD8495/AD8497 Input Overvoltage Performance, 2. 1.50 8 1.00 4 0.50 0 –4 0 –8 –0.50 –12 –1.00 – –30 = 2.7 V Figure 14. AD8496 Input Overvoltage Performance Rev Page ...

Page 9

... Figure 15. AD8494/AD8496 Small-Signal Response with Various Capacitive Loads 120µs/DIV Figure 16. Small-Signal Response 100 kΩ 2V/DIV SETTLING TO 0.1% IN 40µs 0.02%/DIV 100µs/DIV Figure 17. AD8495/AD8497 Large-Signal Step Response and Settling Time C = 0pF 1000pF 4700pF L C ...

Page 10

... AD8494/AD8495/AD8496/AD8497 1s/DIV Figure 21. 0 RTI Voltage Noise –1 –2 –3 –4 –5 1k 10k LOAD RESISTANCE (Ω) Figure 22. Output Voltage Swing vs. Load Resistance, V 100 100 FREQUENCY (Hz) Figure 23. Voltage Noise Spectral Density vs. Frequency (+) –40°C (+) +25° ...

Page 11

... The AD8494 and AD8496 (J type) have an instrumentation amplifier with a gain of 96.7 and 90.35, respectively. • The AD8495 and AD8497 (K type) have an instrumentation amplifier with a gain of 122.4. Rev Page AD8494/AD8495/AD8496/AD8497 Reference Junction ...

Page 12

... AD8497 K ±2°C For temperature ranges outside those listed in Table 7 or for instructions on how to correct for thermocouple nonlinearity error with software, see the product page for the AD8494, AD8495, AD8496, or AD8497, or contact an Analog Devices representative. Rev Page Ambient Measurement Temperature ...

Page 13

... If the ambient temperature sensor configuration is working correctly, the problem typically lies with how the thermocouple is connected to the AD849x. Common errors include an incorrect grounding configuration or lack of filtering. Rev Page AD8494/AD8495/AD8496/AD8497 KEEP JUNCTION AND AD849x AT SAME MEASUREMENT REFERENCE JUNCTION ...

Page 14

... The AD8494 is the best choice for use as an ambient temper- ature sensor. The AD8495, AD8496, and AD8497 can also be configured as ambient temperature sensors, but their output transfer functions are not precisely 5 mV/°C. For information about the exact transfer functions of the AD8494/AD8495/ AD8496/AD8497, see the product page for the AD8494, , also ...

Page 15

... The reference pin can also be used to offset any initial calibra- S tion errors. Apply a small reference voltage proportional to the error to nullify the effect of the calibration error on the output OUT SENSE 1kΩ SETPOINT VOLTAGE S Rev Page AD8494/AD8495/AD8496/AD8497 × 5 mV/° OUT MJ REF ) on S indicates REF ...

Page 16

... AD8497ARMZ 25°C to 100°C AD8497ARMZ-R7 25°C to 100°C AD8497CRMZ 25°C to 100°C AD8497CRMZ-R7 25°C to 100° RoHS Compliant Part. 2 The AD8494 and AD8496 models are prereleased. ©2010 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. ...

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