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Analog Devices Inc. AD7821TQ
- Part No.:
- AD7821TQ
- Manufacturer:
- Analog Devices Inc.
- Category:
- Analog to Digital Converters (ADC)
- Package:
- 20-CDIP (0.300", 7.62mm)
- Datasheet:
-
AD7821TQ.pdf
- Description:
- IC ADC 8BIT PIPELINED 20CDFP
- Quantity:
- Payment:
- Shipping:
Inventory:4,346
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Product details
Overview
AD7821TQ from Analog Devices is a high-speed, 8-bit LC2MOS analog-to-digital converter with integrated track-and-hold, designed for precision data acquisition in demanding environments. It delivers 660 ns conversion time (WR-RD mode), 100 kHz signal bandwidth, ±1 LSB total unadjusted error over –55°C to +125°C, and supports both unipolar (0 V to +5 V) and bipolar (±2.5 V) input ranges. It is used in military-grade instrumentation, avionics sensor interfaces, and high-reliability industrial control systems.
For engineers reviewing the AD7821TQ datasheet, AD7821TQ pinout, AD7821TQ application, or AD7821TQ equivalent, key selection considerations include its extended temperature operation, ratiometric reference capability, no-external-clock half-flash architecture, and compatibility with 68008/8086-style microprocessor buses via CS/RD/WR/INT control signals.
Technical Context
The AD7821TQ implements a half-flash conversion architecture using two cascaded 4-bit flash ADCs - one for MSBs and one for LSBs - eliminating need for external clock generation. Its sampled-data comparators inherently provide track-and-hold functionality, enabling accurate digitization of 100 kHz full-scale sine waves without external circuitry.
It operates in two digital interface modes: RD mode (conversion and read via single READ cycle) and WR-RD mode (separate WRITE-start and READ-read), both synchronized to falling edges of control signals. The MODE pin selects between them, and the VSS pin (Pin 19) enables dual-supply (±5 V) bipolar operation or single-supply (VSS = GND) unipolar operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Resolution | 8 bits - delivers 256 discrete output codes with natural binary (unipolar) or offset binary (bipolar) encoding. |
| Conversion Time | 660 ns max (WR-RD mode) - enables 1 MHz sampling rate, supporting real-time capture of fast transients. |
| Total Unadjusted Error | ±1 LSB max over –55°C to +125°C - ensures guaranteed monotonicity and no missing codes across full military temperature range. |
| Signal-to-Noise Ratio | 45 dB min at 99.85 kHz input - meets dynamic performance requirements for voice and vibration signal digitization. |
| Slew Rate (Tracking) | 1.6 V/µs max - supports faithful digitization of 5 VPP, 100 kHz sine wave without external track-and-hold. |
| Power Dissipation | 50 mW typical at +5 V - compatible with thermally constrained embedded modules and avionics line-replaceable units. |
| Reference Input | Ratiometric VREF(+) and VREF(–) - allows direct use of supply rails as reference, simplifying design and improving noise rejection. |
Pinout & Package
Cerdip (Ceramic Dual In-line Package) Q-20: 20-pin, hermetically sealed, leaded ceramic package rated for –55°C to +125°C operation with high reliability and low moisture ingress.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | VIN | Analog input node; accepts differential reference-defined range (VREF(–) to VREF(+)) - supports ±2.5 V bipolar or 0–5 V unipolar inputs. |
| 2–5, 14–17 | DB0–DB7 | Three-state parallel data outputs (LSB to MSB); latched and bus-compatible with 8086/68000-family microprocessors. |
| 6 | WR/RDY | Configurable pin: WR input in WR-RD mode; RDY open-drain status output in RD mode - eliminates need for WAIT-state logic in microprocessor interfacing. |
| 7 | MODE | Mode selection control; internal 50 µA pull-down - sets interface timing behavior (RD vs. WR-RD) without external biasing. |
| 8 | RD | Read strobe input; active-low - enables data output buffer and triggers conversion completion handshake in RD mode. |
| 9 | INT | Interrupt output; active-low - signals conversion completion with 380 ns typical delay after WR rising edge, enabling deterministic DSP sampling. |
| 10 | GND | Digital ground reference - separate from analog ground path per layout best practices to minimize noise coupling. |
| 11–12 | VREF(–), VREF(+) | Differential reference span terminals - define zero and full-scale points; support ratiometric operation and flexible input scaling. |
| 13 | CS | Chip select input; active-low - enables device decoding on shared data/address buses and controls power-down current (ISS ≤ 100 µA). |
| 18 | OFL | Overflow flag output; active-low - indicates input > (VREF(+) – ½ LSB); enables cascading for higher-resolution applications. |
| 19 | VSS | Negative supply terminal - tied to –5 V for bipolar operation or GND for unipolar mode; defines analog input common-mode range. |
| 20 | VDD | Positive supply input - requires +5 V ±5%; powers analog core and digital interface with 20 mA max IDD under active conversion. |
Key Features
| Feature | Design Value |
|---|---|
| No external clock required | Half-flash architecture self-times conversion - removes clock distribution complexity and jitter sensitivity in embedded systems. |
| Built-in track-and-hold | 100 kHz analog input bandwidth achieved without external THS - reduces BOM count and PCB area in space-constrained designs. |
| Ratiometric reference inputs | VREF(+) and VREF(–) accept supply-derived references - maintains accuracy despite rail variation, ideal for battery-powered or unregulated systems. |
| Extended temperature grade | –55°C to +125°C operation with ±1 LSB error guarantee - qualified for aerospace, downhole, and engine-control applications. |
| Microprocessor-compatible interface | Standard CS/RD/WR/INT signaling with three-state outputs - integrates directly with 8086, 68000, and Z80 buses without glue logic. |
Applications
| Avionics Sensor Interface | Military Data Acquisition |
|---|---|
|
Use Scenario: Digitizing accelerometer and gyroscope outputs in flight control units under extreme thermal cycling and EMI exposure. IC Role / Device Role / Timing Role: ADC front-end with built-in track-and-hold; samples inertial signals at 500 kHz with deterministic WR-edge-triggered timing. Use Value: Eliminates external THS and clock generator, reducing SWaP-C while maintaining ±1 LSB accuracy across –55°C to +125°C. |
Use Scenario: High-speed waveform capture in portable electronic warfare receivers requiring wide dynamic range and low distortion. IC Role / Device Role / Timing Role: Precision sampling stage in IF chain; uses ratiometric reference to reject supply noise during pulsed RF operation. Use Value: 45 dB SNR and –50 dB THD at 100 kHz enable detection of weak signals amid strong interferers without calibration drift. |
| Industrial Motor Drive Feedback | Downhole Telemetry Systems |
|
Use Scenario: Real-time current and voltage sensing in servo drives operating near induction heating equipment. IC Role / Device Role / Timing Role: Isolated analog input conditioner feeding FPGA-based control loop; uses OFL pin for overcurrent detection. Use Value: 1.6 V/µs slew rate and 660 ns conversion allow closed-loop response within 1 µs, improving torque ripple suppression. |
Use Scenario: Pressure and temperature monitoring in oil/gas well logging tools exposed to 150°C ambient and shock/vibration. IC Role / Device Role / Timing Role: Ruggedized ADC in high-temp ASIC subsystem; operates from ±5 V supplies with VSS referenced to local analog ground. Use Value: Cerdip Q-20 package and –55°C to +125°C rating ensure long-term reliability where plastic packages would fail. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 8-bit, high-speed ADC applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| AD7821BQ | Same architecture and pinout; rated for –40°C to +85°C only - lower thermal margin, 100 µA max ISS vs. 100 µA for TQ. | Commercial/industrial systems without extended temperature requirement - unsuitable for aerospace or downhole use. | Select AD7821BQ only when full military temperature range is not needed and cost optimization is prioritized. |
| MAX118ACPP | 10-bit resolution, 1.5 µs conversion, +5 V only, no VSS pin - lacks bipolar support and extended temp grade; uses external clock. | General-purpose test equipment or lab instruments where resolution > speed and temperature range are primary concerns. | Choose MAX118ACPP if 10-bit resolution outweighs need for 100 kHz THS bandwidth and –55°C operation. |
Compared with AD7821BQ, the AD7821TQ provides guaranteed ±1 LSB error at +125°C and hermetic Q-20 packaging for harsh environments; compared with MAX118ACPP, it trades 2-bit resolution for 2.3× faster conversion, integrated THS, and true bipolar capability - making it optimal for deterministic, high-reliability sampling.
Availability
AD7821TQ is available at Aetrix Electronics and suitable for avionics sensor interfaces, military data acquisition systems, and downhole telemetry requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for AD7821TQ 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 precision instrumentation, communications, and industrial markets since 1965.
The AD7821TQ belongs to Analog Devices' LC2MOS high-speed ADC product line, engineered for applications demanding fast, accurate digitization in thermally extreme and electrically noisy environments - especially where microprocessor interfacing simplicity and supply insensitivity are critical.
FAQ
What is the maximum analog input frequency supported by the AD7821TQ without external track-and-hold?
The AD7821TQ supports analog input frequencies up to 100 kHz maximum in unfiltered conditions due to its inherent track-and-hold function, verified by 5 VPP sine wave testing. This is enabled by its sampled-data comparator architecture and 1.6 V/µs tracking slew rate - no external THS is required for full-scale 100 kHz signals, making the AD7821TQ suitable for vibration monitoring and motor phase current sensing where board space is constrained.
Does the AD7821TQ require an external clock signal to operate?
No, the AD7821TQ does not require an external clock signal. Its half-flash conversion technique uses internal timing generators, allowing full operation with only CS, RD, and WR control signals. This eliminates clock distribution challenges and jitter-related SNR degradation - a key advantage of the AD7821TQ in EMI-prone avionics and industrial settings where clean clock routing is impractical.
How does the AD7821TQ achieve bipolar input operation?
The AD7821TQ achieves bipolar input operation by connecting VSS (Pin 19) to –5 V and configuring VREF(–) = –2.5 V and VREF(+) = +2.5 V, resulting in a ±2.5 V input range with offset binary coding. This configuration is explicitly validated in the AD7821TQ datasheet specifications and timing diagrams - unlike unipolar mode (VSS = GND), bipolar mode requires dual supplies but retains the same ±1 LSB total unadjusted error guarantee across –55°C to +125°C.
What is the meaning of "T" in the AD7821TQ part number?
The "T" in AD7821TQ denotes the extended temperature grade, specifying operation from –55°C to +125°C - confirmed in the Ordering Guide and Absolute Maximum Ratings tables. This distinguishes the AD7821TQ from K/B versions (–40°C to +85°C) and qualifies it for deployment in jet engine compartments, space-rated payloads, and geothermal drilling tools where commercial-grade parts would fail.
Can the AD7821TQ interface directly with an 8086 microprocessor bus?
Yes, the AD7821TQ interfaces directly with an 8086 microprocessor bus using standard memory-mapped or I/O-mapped protocols. Its CS/RD/WR/INT signaling, three-state DB0–DB7 outputs, and RDY/WR-RD mode flexibility eliminate need for address decoders or bus transceivers - demonstrated in the AD7821 datasheet's 68008 interface example, which shares identical timing and electrical compatibility with the 8086 family. The AD7821TQ's 700 ns RD-mode conversion time aligns with 8086 wait-state requirements.
AD7821TQ Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-CDIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Active
- Number of Bits:
- 8
- Sampling Rate (Per Second):
- 1M
- Number of Inputs:
- 1
- Input Type:
- Single Ended
- Data Interface:
- Parallel
- Configuration:
- S/H-ADC
- Ratio - S/H:ADC:
- 1:1
- Number of A/D Converters:
- 1
- Architecture:
- Pipelined
- Reference Type:
- External
- Voltage - Supply, Analog:
- 5V
- Voltage - Supply, Digital:
- 5V
- Features:
- -
- Operating Temperature:
- -55°C ~ 125°C
- Supplier Device Package:
- 20-CERDIP
- Mounting Type:
- Through Hole
- Grade:
- -
- Qualification:
- -
AD7821TQ FAQ
1.How can I place an order for AD7821TQ through Aetrix?
Please submit a Request for Quotation (RFQ) for AD7821TQ 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 AD7821TQ reliable?
The price and inventory of AD7821TQ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for AD7821TQ is usually 5 days.
3.What payment methods are accepted for AD7821TQ?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for AD7821TQ transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for AD7821TQ?
AD7821TQ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your AD7821TQ 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 AD7821TQ?
For technical support, including AD7821TQ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your AD7821TQ requirements.
6.How does Aetrix verify that AD7821TQ is sourced from the original manufacturer or authorized distributors?
All AD7821TQ 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 AD7821TQ meets industry standards.
7.What is the process for return or replacement of AD7821TQ?
All AD7821TQ units undergo pre-shipment inspection (PSI). If there is an issue with AD7821TQ, 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 AD7821TQ part is unused and in its original packaging.
Return procedure for AD7821TQ:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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