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부품번호 ADC8494 기능
기능 (ADC8494 - ADC8497) Precision Thermocouple Amplifiers
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ADC8494 데이터시트, 핀배열, 회로
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
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
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 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. C
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.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
FUNCTIONAL BLOCK DIAGRAM
REF
+IN ESD AND
OVP
AD8494/AD8495/
AD8496/AD8497
A2
THERMO-
COUPLE
COLD JUNCTION
COMPENSATION
A3
–IN
1M
ESD AND
OVP
A1
Figure 1.
SENSE
OUT
Table 1. Device Temperature Ranges
Thermo-
Optimized Temperature Range
Couple Ambient Temperature Measurement
Part No. Type
(Reference Junction) Junction
AD8494 J
0°C to 50°C
Full J type range
AD8495 K
0°C to 50°C
Full K type range
AD8496 J
25°C to 100°C
Full J type range
AD8497 K
25°C to 100°C
Full K type range
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. Complete, precision laser wafer trimmed thermocouple
signal conditioning system in a single IC package.
2. Flexible pinout provides for operation as a setpoint
controller or as a standalone Celsius thermometer.
3. Rugged inputs withstand 4 kV ESD and provide over-
voltage protection (OVP) up to VS ± 25 V.
4. Differential inputs reject common-mode noise on the
thermocouple leads.
5. Reference pin voltage can be offset to measure 0°C on
single supplies.
6. Available in a small, 8-lead MSOP that is fully RoHS compliant.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2010–2011 Analog Devices, Inc. All rights reserved.
Free Datasheet http://www.datasheet4u.com/




ADC8494 pdf, 반도체, 판매, 대치품
AD8494/AD8495/AD8496/AD8497
A Grade
C Grade
Parameter
Test Conditions/Comments Min
Typ Max
Min
Typ Max
Unit
TEMPERATURE RANGE (TA)
Specified Performance
AD8494/AD8495
0 50 0 50 °C
AD8496/AD8497
25 100 25 100 °C
Operational
−40
+125
−40
+125
°C
1 Ambient temperature rejection specifies the change in the output measurement (in °C) for a given change in temperature of the cold junction. For the AD8494 and
AD8495, ambient temperature rejection is defined as the slope of the line connecting errors calculated at 0°C and 50°C ambient temperature. For the AD8496 and
AD8497, ambient temperature rejection is defined as the slope of the line connecting errors calculated at 25°C and 100°C ambient temperature.
2 Error does not include thermocouple gain error or thermocouple nonlinearity.
3 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 5 V or a 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.
4 Input stage uses PNP transistors, so bias current always flows out of the part.
5 Large output currents can increase the internal temperature rise of the part and contribute to cold junction compensation (CJC) error.
6 Unbalanced supplies can also be used. Care should be taken that the common-mode voltage of the thermocouple stays within the input voltage range of the part.
Rev. C | Page 4 of 16
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ADC8494 전자부품, 판매, 대치품
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, +VS = 5 V, RL = ∞, unless otherwise noted.
100
AD8495/AD8497
AD8494
AD8496
10
1
0.1
0.01
0.1
1 10 100 1k
FREQUENCY (Hz)
Figure 3. CMRR vs. Frequency
10k
100k
1000
100
AD8495/AD8497
AD8494
AD8496
10
1
0
1 10 100 1k 10k 100k
FREQUENCY (Hz)
Figure 4. PSRR vs. Frequency
50
40
30
20
10
0
–10
–20
100
AD8494
AD8496
AD8495/AD8497
1k 10k 100k
FREQUENCY (Hz)
Figure 5. Frequency Response
1M
AD8494/AD8495/AD8496/AD8497
1200
1000
800
CONNECTED
THERMOCOUPLE
600
400
200
0
–200
OPEN THERMOCOUPLE
THERMOCOUPLE CONNECTION
AD849x OUTPUT
TIME (50µs/DIV)
Figure 6. Output Response to Open Thermocouple,
−IN Connected to Ground Through a 1 MΩ Resistor
4.0
3.5 +0.05, +3.45
3.0 +0.05, +3.21
2.5
+4.91, +2.95
+4.91, +2.71
2.0
1.5
1.0
0.5
0
+0.05, –0.36
+4.91, –0.37
–0.5 +0.05, –0.39
VREF = 0V
+4.91, –0.39
–1.0
VREF = 2.5V
–0.5 0.5 1.5 2.5 3.5 4.5 5.5
OUTPUT VOLTAGE (V)
Figure 7. Input Common-Mode Voltage Range vs. Output Voltage,
+VS = 5 V, VREF = 0 V, and VREF = 2.5 V
40 2.00
35 1.75
30 1.50
IBIAS
25 1.25
20 1.00
15 0.75
10 0.50
5 0.25
0
–40 –20
0
IOS
20 40 60
0
80 100 120
TEMPERATURE (°C)
Figure 8. Input Bias Current and Input Offset Current vs. Temperature
Rev. C | Page 7 of 16
Free Datasheet http://www.datasheet4u.com/

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