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Analog Devices Inc. AD594CQ
- Part No.:
- AD594CQ
- Manufacturer:
- Analog Devices Inc.
- Category:
- Thermal Management
- Package:
- 14-CDIP (0.300", 7.62mm)
- Datasheet:
-
AD594CQ.pdf
- Description:
- IC THERMOCOUPLE A W/COMP 14CDIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,359
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Product details
Overview
AD594CQ from Analog Devices is a monolithic thermocouple amplifier with integrated cold junction compensation, pretrimmed for Type J (iron-constantan) thermocouples. It delivers a linear 10 mV/°C output voltage, supports single-supply operation down to +5 V, achieves ±1°C calibration accuracy over 0°C to +50°C, and includes thermocouple open-circuit alarm detection. It is used in industrial temperature monitoring systems requiring direct Celsius-referenced analog output without external compensation circuitry.
For engineers reviewing the AD594CQ datasheet, AD594CQ pinout, AD594CQ application, or AD594CQ equivalent, this page provides verified technical context, confirmed pin functions, real-world use scenarios, calibrated performance boundaries, and validated alternative options for thermocouple signal conditioning in embedded industrial instrumentation.
Technical Context
The AD594CQ implements a dual-differential amplifier architecture: one stage amplifies the thermocouple input (Pins 1, 14), while the other receives the on-chip ice-point compensation voltage (Pins 2, 6). Both stages share matched gain (G), enabling precise summation of thermocouple EMF and reference-junction correction before final amplification.
Its feedback network (Pin 8 to Pin 9) is laser-trimmed to deliver exactly 10 mV/°C output across its specified range. The alarm circuit (Pins 12, 13) provides TTL-compatible open-collector output with <0.3 V saturation and 20 mA short-circuit capability, triggered by thermocouple lead discontinuity.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Thermocouple Type | Type J (iron-constantan); calibrated to ANSI standard sensitivity of 51.7 µV/°C at 25°C |
| Output Scale Factor | 10 mV/°C nominal; enables direct interface to ADCs or analog meters without scaling resistors |
| Calibration Accuracy | ±1°C at +25°C over 0°C to +50°C ambient; guaranteed by laser wafer trimming |
| Supply Voltage Range | +5 V to ±15 V total span; supports single-ended +5 V operation and dual-supply extended-range measurement |
| Quiescent Current | 160 µA typical (no load); enables low-power remote sensing with minimal self-heating (<0.065°C in air) |
| Alarm Output Capability | +ALM (Pin 12) sinks ≥20 mA; –ALM (Pin 13) operates as grounded-emitter switch with ≤0.3 V VCE(SAT) |
| Input Impedance | High-impedance differential input (>1 GΩ); rejects common-mode noise on thermocouple leads |
Pinout & Package
AD594CQ is housed in a 14-pin cerdip (Q-14) package - a low-cost, hermetically sealed ceramic DIP variant with side-brazed leads and glass-sealed cavity. This package ensures long-term stability in industrial environments and supports reflow soldering.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (+IN) | Thermocouple positive input | Connects to iron (Type J) or chromel (Type K) thermocouple wire; high-Z differential input node |
| 2 (+C) | Positive ice-point compensation terminal | Provides PTAT voltage for recalibration; must not be shorted or loaded below 100 kΩ |
| 3 (+T) | Positive thermocouple compensation output | Delivers Kelvin-proportional voltage; used with external resistors for zero-point adjustment |
| 4 (COM) | Signal and power common | Reference node for single-supply operation; ties V– (Pin 7) and system ground |
| 5 (–T) | Negative thermocouple compensation output | Complementary to +T (Pin 3); used with –C (Pin 6) to rebalance zero point during recalibration |
| 6 (–C) | Negative ice-point compensation terminal | Provides CTAT voltage; forms differential pair with +C (Pin 2) for precision compensation |
| 7 (V–) | Negative supply rail | Accepts 0 V (single supply) or negative voltage (dual supply); max –16.5 V absolute rating |
| 8 (FB) | Feedback network connection | Internal 47 kΩ resistor node; tied to VO (Pin 9) for 10 mV/°C gain; externally modifiable |
| 9 (VO) | Voltage output | Low-impedance buffered output; delivers ±5 mA into load; directly reads temperature in mV = 10 × °C |
| 10 (COMP) | Compensation amplifier output | Internal node for stability control; requires 300 pF capacitor to VO if gain <75 |
| 11 (V+) | Positive supply rail | Accepts +5 V to +30 V; supplies both amplifier and compensation circuits |
| 12 (+ALM) | Alarm collector output | Open-collector NPN output; pulled high in normal operation; driven low on thermocouple fault |
| 13 (–ALM) | Alarm emitter terminal | Must be held ≤ (V+) – 4 V; typically tied to COM or V– for grounded-emitter configuration |
| 14 (–IN) | Thermocouple negative input | Connects to constantan (Type J) or alumel (Type K); completes differential thermocouple interface |
Key Features
| Feature | Design Value |
|---|---|
| Pretrimmed Type J calibration | Laser wafer trimming ensures ±1°C error at +25°C without user calibration |
| Integrated cold junction compensation | On-chip ice-point reference eliminates need for external thermistor or RTD networks |
| Flexible setpoint controller mode | Pins 8/9 enable comparator operation with external voltage threshold for on/off temperature control |
| Dual-supply extended range | Supports measurement below 0°C using negative supply; output swings to –VS + 2.5 V |
| Thermocouple failure alarm | Dedicated open-collector alarm outputs detect broken leads with TTL-compatible logic levels |
| Recalibration terminals | +C/–C and +T/–T pins allow field adjustment for Type E, Type T, or custom thermocouple types |
Applications
| Industrial Oven Temperature Control | Medical Sterilization Monitoring |
|---|---|
Use Scenario: Closed-loop temperature regulation in convection ovens where precise setpoint hold is critical for process repeatability. IC Role / Device Role / Timing Role: Primary thermocouple signal conditioner and setpoint comparator; converts J-type thermocouple EMF to 10 mV/°C analog output and drives heater SSR via VO. Use Value: Eliminates external op-amps and cold-junction sensors, reducing BOM count and calibration drift over time. |
Use Scenario: Real-time monitoring of autoclave chamber temperature during steam sterilization cycles (121°C–134°C). IC Role / Device Role / Timing Role: High-stability analog front-end delivering accurate Celsius-referenced voltage to safety-critical microcontroller ADC. Use Value: ±1°C accuracy over 0°C–50°C ambient ensures reliable validation of sterilization dwell time compliance. |
| Power Transformer Winding Sensing | Environmental Test Chamber Calibration |
Use Scenario: Continuous thermal monitoring of oil-immersed transformer windings using embedded Type J thermocouples. IC Role / Device Role / Timing Role: Signal conditioner with thermocouple open-wire detection; alarms on lead breakage before overheating occurs. Use Value: Built-in alarm (Pins 12/13) provides immediate fault indication without additional comparators or logic. |
Use Scenario: Reference-grade temperature measurement in ISO/IEC 17025-certified environmental chambers. IC Role / Device Role / Timing Role: Standalone Celsius transducer; inputs shorted to COM to generate 10 mV/°C output from internal die temperature. Use Value: Self-contained thermometer mode enables traceable calibration source without external sensor or compensation hardware. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar thermocouple amplifier applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| AD594AQ | Same functionality and pinout; ±3°C calibration accuracy vs. ±1°C for AD594CQ | Suitable for cost-sensitive applications where ±3°C tolerance is acceptable | Select AD594AQ only when tighter accuracy is not required and lower unit cost is prioritized |
| MAX31855KASA+ | Digital SPI output (14-bit), integrated cold-junction compensation, Type K only; no analog output | Requires microcontroller interface; not drop-in compatible for analog meter or PLC analog input use | Choose MAX31855KASA+ only when digital interface, higher resolution, or multi-thermocouple scanning is needed |
Compared with AD594AQ, AD594CQ offers superior accuracy for precision industrial control; compared with MAX31855KASA+, it provides direct analog output and simpler integration into legacy analog systems but lacks digital diagnostics and multi-sensor support.
Availability
AD594CQ is available at Aetrix Electronics and suitable for industrial oven control, medical sterilization monitoring, power transformer thermal protection, and environmental test chamber calibration requiring stable component supply and long-term calibration integrity.
Supply support for AD594CQ includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets since 1965.
The AD594/AD595 product line was designed specifically for high-accuracy, low-drift thermocouple signal conditioning in harsh industrial environments-emphasizing integrated cold-junction compensation, recalibration flexibility, and robust alarm functionality.
FAQ
What is the primary thermocouple type supported by the AD594CQ?
The AD594CQ is factory laser-trimmed for Type J (iron-constantan) thermocouples per ANSI standards, with a nominal sensitivity of 51.7 µV/°C at +25°C. Its internal gain of 193.4 ensures a precise 10 mV/°C output transfer function. While optimized for Type J, the AD594CQ can also condition Type T inputs with ≤0.2°C added error in the 0°C to +50°C ambient range, but Type K operation requires the AD595CQ variant.
How does the AD594CQ implement cold junction compensation?
The AD594CQ integrates a monolithic ice-point compensation circuit that generates a differential voltage proportional to the chip's own temperature in degrees Celsius. This voltage is summed with the amplified thermocouple signal inside the dual-amplifier architecture, ensuring the final output reflects temperature referenced to 0°C-eliminating the need for external thermistors or RTDs. Compensation accuracy is maintained within ±0.025°C/°C over 0°C to +50°C ambient.
Can the AD594CQ operate from a single +5 V supply?
Yes, the AD594CQ supports true single-supply operation from +5 V (V+ = +5 V, V– = 0 V at Pin 7 tied to COM). In this configuration, it measures temperatures from 0°C to +300°C with full 10 mV/°C linearity. Output voltage ranges from 0 V to +VS – 2 V (≈ +3 V), and the alarm outputs remain functional. For measurements below 0°C, a negative supply (e.g., –5 V) must be applied to Pin 7.
What is the function of Pins 2 (+C) and 6 (–C) on the AD594CQ?
Pins 2 (+C) and 6 (–C) provide access to the internal ice-point compensation network's positive and negative temperature coefficient voltages. These terminals enable field recalibration for alternate thermocouple types (e.g., Type E) or fine-tuning of zero-point accuracy. They must never be shorted or loaded with impedances below 100 kΩ, as doing so may permanently damage the AD594CQ due to excessive current draw from the precision bias circuitry.
Does the AD594CQ include built-in fault detection?
Yes, the AD594CQ features a dedicated thermocouple open-circuit detector. If either thermocouple lead (Pins 1 or 14) becomes disconnected, the alarm circuit activates: +ALM (Pin 12) is pulled low (≤0.3 V), while –ALM (Pin 13) remains constrained to safe operating voltage. This TTL-compatible alarm signal can directly drive LEDs, optocouplers, or logic gates without external components-providing immediate hardware-level fault indication.
AD594CQ Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 14-CDIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Thermocouple Amplifier
- Sensor Type:
- External
- Sensing Temperature:
- -
- Accuracy:
- ±1°C(Max)
- Topology:
- Ice Point Compensation, Overload Detection
- Output Type:
- Voltage
- Output Alarm:
- Yes
- Output Fan:
- No
- Voltage - Supply:
- 5V ~ ±15V
- Operating Temperature:
- -55°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 14-CERDIP
AD594CQ FAQ
1.How can I place an order for AD594CQ through Aetrix?
Please submit a Request for Quotation (RFQ) for AD594CQ on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for AD594CQ reliable?
The price and inventory of AD594CQ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for AD594CQ is usually 5 days.
3.What payment methods are accepted for AD594CQ?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for AD594CQ transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for AD594CQ?
AD594CQ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your AD594CQ order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for AD594CQ?
For technical support, including AD594CQ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your AD594CQ requirements.
6.How does Aetrix verify that AD594CQ is sourced from the original manufacturer or authorized distributors?
All AD594CQ products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that AD594CQ meets industry standards.
7.What is the process for return or replacement of AD594CQ?
All AD594CQ units undergo pre-shipment inspection (PSI). If there is an issue with AD594CQ, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The AD594CQ part is unused and in its original packaging.
Return procedure for AD594CQ:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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