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Precision Thermocouple Amplifiers with Cold Junction Compensation AD8494/AD8495/AD8496/AD8497
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 and 0.025°C/°C ambient temperature rejection Low power: <1 mW at VS = 5 V Wide power supply range Single supply: 2.7 V to 36 V Dual supply: ±2.7 V to ±18 V Small, 8-lead MSOP
FUNCTIONAL BLOCK DIAGRAM
REF
+IN
ESD AND OVP
AD8494/AD8495/ AD8496/AD8497
A2
THERMOCOUPLE
COLD JUNCTION COMPENSATION
A3
OUT
–IN 1MΩ
ESD AND OVP
A1
SENSE
Figure 1.
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
Table 1. Device Temperature Ranges
ThermoCouple Type J K J K Optimized Temperature Range Ambient Temperature Measurement (Reference Junction) Junction 0°C to 50°C Full J type range 0°C to 50°C Full K type range 25°C to 100°C Full J type range 25°C to 100°C Full K type range
Part No. AD8494 AD8495 AD8496 AD8497
GENERAL DESCRIPTION
The AD8494/AD8495/AD8496/AD8497 are precision instrumentation 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 selfheating, 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) thermocouples. See Table 1 for the optimized ambient temperature range of each part.
Rev. C
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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 thermocouple’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. 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 overvoltage protection (OVP) up to VS ± 25 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.
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Free Datasheet http://www.datasheet4u.com/
08529-001
AD8494/AD8495/AD8496/AD8497 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Product Highlights ........................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 Thermal Resistance ...............................................