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Analog Devices Inc. AD7821BQ
- Part No.:
- AD7821BQ
- Manufacturer:
- Analog Devices Inc.
- Category:
- Analog to Digital Converters (ADC)
- Package:
- 20-CDIP (0.300", 7.62mm)
- Datasheet:
-
AD7821BQ.pdf
- Description:
- IC ADC 8BIT PIPELINED 20CDFP
- Quantity:
- Payment:
- Shipping:
Inventory:1,156
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Product details
Overview
AD7821BQ from Analog Devices is an LC2MOS 8-bit analog-to-digital converter with integrated track-and-hold, 660 ns conversion time (WR-RD mode), ±1 LSB total unadjusted error over –40°C to +85°C, and support for both unipolar (0 V to +5 V) and bipolar (±2.5 V) input ranges. It interfaces directly to microprocessor buses using CS, RD, WR, RDY, and INT signals and delivers 1 MHz sample rate for high-speed data acquisition in DSP and instrumentation systems.
For engineers reviewing the AD7821BQ datasheet, AD7821BQ pinout, AD7821BQ application, or AD7821BQ equivalent, key selection considerations include its half-flash architecture eliminating external clock dependency, built-in 100 kHz track-and-hold enabling direct digitization of full-scale sine waves without external circuitry, ratiometric reference inputs, and compatibility with standard 8-bit microprocessor control protocols.
Technical Context
The AD7821BQ implements a half-flash conversion architecture using two cascaded 4-bit flash ADCs - one for MSBs and one for LSBs - with internal DAC feedback and comparator-based sampling. Its sampling instant is precisely defined on the falling edge of WR (WR-RD mode) or RD (RD mode), ensuring deterministic timing for jitter-sensitive applications like digital signal processing.
It operates in two configurable interface modes: RD mode (MODE = 0), where CS+RD initiates and reads conversion in a single stretched read cycle, and WR-RD mode (MODE = 1), where WR starts conversion and RD reads result - supporting both WAIT-state-capable and WAIT-free microprocessors. The VSS pin (Pin 19) enables dual-supply (±5 V) operation for bipolar inputs or single-supply (VSS = GND) for unipolar use.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Resolution | 8 bits - delivers 256 discrete output codes with 19.53 mV LSB step size in both unipolar and bipolar modes. |
| Conversion Time | 660 ns max (WR-RD mode) - enables real-time sampling at up to 1 MHz without external clock generation. |
| Total Unadjusted Error | ±1 LSB max over –40°C to +85°C - ensures monotonicity and no missing codes across full industrial temperature range. |
| Track-and-Hold Bandwidth | 100 kHz max - supports direct digitization of full-scale 5 VPP sine waves without external T/H circuitry. |
| Signal-to-Noise Ratio | 45 dB min at 99.85 kHz input - meets dynamic performance requirements for voice recognition and echo cancellation. |
| Power Dissipation | 50 mW typical at +5 V supply - compatible with low-power embedded systems and thermally constrained layouts. |
| Input Slew Rate | 1.6 V/µs max - defines maximum allowable input voltage change during tracking to maintain 8-bit accuracy. |
Pinout & Package
Cerdip (Ceramic Dual In-line Package) with 20 terminals, hermetically sealed, suitable for high-reliability industrial environments and extended temperature operation (–40°C to +85°C).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 1) | Analog Input | Accepts differential input range from VREF(–) to VREF(+); supports unipolar (0 V to +5 V) or bipolar (–2.5 V to +2.5 V) configurations. |
| DB0–DB7 (Pins 2–5, 14–17) | Three-State Data Outputs | Latched 8-bit parallel output bus compatible with TTL/CMOS logic; tri-stated when CS or RD is high. |
| WR/RDY (Pin 6) | Mode-Dependent Control/Status | In WR-RD mode: WR input triggers conversion on falling edge; in RD mode: RDY open-drain status output indicates conversion completion. |
| MODE (Pin 7) | Interface Mode Selection | High = WR-RD mode; Low = RD mode; internally pulled low via 50 µA current source for default RD operation. |
| RD (Pin 8) | Read Control Input | Active-low signal enabling data output latch and reading DB0–DB7; resets INT on rising edge. |
| INT (Pin 9) | Interrupt Output | Open-drain active-low signal indicating conversion completion; reset by rising edge of CS or RD. |
| GND (Pin 10) | Ground Reference | Common return path for analog and digital sections; requires low-impedance connection to minimize noise coupling. |
| VREF(–) (Pin 11) | Reference Lower Bound | Defines negative end of reference span; accepts VSS ≤ VREF(–) ≤ VREF(+); enables ratiometric operation. |
| VREF(+) (Pin 12) | Reference Upper Bound | Defines positive end of reference span; accepts VREF(–) < VREF(+) ≤ VDD; sets full-scale range with VREF(–). |
| CS (Pin 13) | Chip Select Input | Active-low enable for device addressing; required low for all control operations and data access. |
| OFL (Pin 18) | Overflow Flag Output | Active-low non-tri-state output signaling input > (VREF(+) – ½ LSB); used for cascading multiple AD7821BQ units to extend resolution. |
| VSS (Pin 19) | Negative Supply | Connect to –5 V for bipolar operation or to GND for unipolar +5 V supply configuration. |
| VDD (Pin 20) | Positive Supply | +5 V ±5% supply input; powers analog core and digital interface; decoupling recommended per datasheet. |
Key Features
| Feature | Design Value |
|---|---|
| No external clock required | Half-flash architecture eliminates need for CLK generation circuitry, reducing BOM count and layout complexity. |
| Built-in 100 kHz track-and-hold | Enables accurate digitization of fast-changing signals up to 100 kHz without external components or timing calibration. |
| Ratiometric reference inputs | VREF(+) and VREF(–) allow system-level scaling where reference tracks sensor excitation or supply rails, improving measurement stability. |
| Microprocessor-compatible interface | Standard CS/RD/WR/INT/RDY signals simplify integration with 68000-, 80x86-, and Z80-based systems without glue logic. |
| Low power dissipation | 50 mW typical at +5 V allows use in thermally sensitive or battery-backed instrumentation without forced cooling. |
Applications
| Data Acquisition System | DSP-Based Voice Recognition |
|---|---|
Use Scenario: High-speed sampling of sensor outputs (e.g., accelerometers, pressure transducers) in industrial PLCs and test equipment. IC Role / Device Role / Timing Role: Primary ADC capturing analog signals at up to 1 MHz with precise sampling edges synchronized to WR/RD control lines. Use Value: 660 ns conversion time and ±1 LSB error ensure minimal latency and high fidelity in closed-loop control feedback paths. | Use Scenario: Digitizing microphone or line-level audio signals for real-time spectral analysis in embedded voice recognition engines. IC Role / Device Role / Timing Role: Front-end ADC providing 45 dB SNR and –50 dB THD at 100 kHz input, sampled with equidistant intervals controlled by WR edge. Use Value: Built-in track-and-hold and deterministic sampling eliminate need for external anti-aliasing filters and reduce system component count. |
| Industrial Process Monitoring | Automated Test Equipment (ATE) |
Use Scenario: Continuous monitoring of analog process variables (temperature, flow, voltage) in harsh factory-floor environments. IC Role / Device Role / Timing Role: Rugged Cerdip-packaged ADC operating reliably from –40°C to +85°C with bipolar input capability for differential sensor interfaces. Use Value: VSS pin enables true ±5 V dual-supply operation, allowing direct interfacing to isolated current-loop transmitters and bridge sensors. | Use Scenario: High-throughput stimulus-response testing of analog circuits using programmable waveform generators and precision digitizers. IC Role / Device Role / Timing Role: Fast, repeatable ADC with overflow flag (OFL) supporting multi-device cascading for enhanced resolution in boundary-scan or functional test fixtures. Use Value: OFL output enables seamless 16-bit extension by chaining two AD7821BQ units, avoiding costly higher-resolution alternatives. |
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 |
|---|---|---|---|
| AD7820KN | Slower 1.36 µs conversion time; no built-in track-and-hold; requires external T/H for >6.4 kHz signals. | Suitable only for lower-bandwidth DC or slow-varying measurements; not viable for 100 kHz signal capture. | Select AD7821BQ when sampling bandwidth >10 kHz or when minimizing external components is critical. |
| MAX1112CPE+ | Serial SPI interface; 2.5 µs conversion; 8-bit resolution; single +5 V supply only; no bipolar input support. | Designed for space-constrained PCBs with serial bus infrastructure; lacks parallel bus compatibility and dual-supply flexibility. | Choose AD7821BQ for parallel microprocessor interfacing, bipolar operation, or deterministic WR-edge sampling in real-time systems. |
Compared with AD7820KN and MAX1112CPE+, the AD7821BQ uniquely combines sub-microsecond conversion, integrated track-and-hold, bipolar/unipolar configurability, and parallel microprocessor interface - making it optimal for industrial data loggers and DSP front-ends requiring deterministic timing and minimal external circuitry.
Availability
AD7821BQ is available at Aetrix Electronics and suitable for industrial process monitoring, automated test equipment, data acquisition systems, and DSP-based voice recognition requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for AD7821BQ 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, communications, automotive, and consumer markets since 1965.
The AD7821BQ belongs to Analog Devices' precision high-speed ADC product line, designed specifically for applications demanding fast, accurate digitization of analog signals in resource-constrained embedded systems with minimal external support circuitry.
FAQ
What is the maximum analog input frequency the AD7821BQ can accurately digitize without an external track-and-hold?
The AD7821BQ features an inherent track-and-hold function rated for 100 kHz maximum input signal bandwidth. This means it can accurately digitize full-scale 5 VPP sine waves up to 100 kHz without external components. The specification is verified under conditions of VREF(+) = 2.5 V, VREF(–) = –2.5 V, and fSAMPLING = 500 kHz, and applies directly to the AD7821BQ in both unipolar and bipolar configurations.
Does the AD7821BQ require an external clock signal to operate?
No, the AD7821BQ does not require an external clock. Its half-flash conversion architecture generates internal timing, allowing operation solely from WR and RD control signals. This eliminates clock distribution challenges and reduces system-level jitter - a confirmed design feature of the AD7821BQ as documented in its functional block diagram and timing specifications.
How does the MODE pin affect the digital interface behavior of the AD7821BQ?
The MODE pin selects between two distinct interface protocols: when low, AD7821BQ operates in RD mode (Pin 6 = RDY status output); when high, it operates in WR-RD mode (Pin 6 = WR input). This dual-mode capability allows the AD7821BQ to interface seamlessly with both WAIT-state-capable microprocessors (e.g., 68000 family) and WAIT-free controllers (e.g., certain 8051 derivatives), as confirmed in the Digital Interface section of the AD7821BQ datasheet.
Can the AD7821BQ be used with a single +5 V supply for bipolar input measurements?
No - bipolar input operation requires dual supplies: VDD = +5 V and VSS = –5 V. The AD7821BQ's VSS pin (Pin 19) must be connected to –5 V to establish the –2.5 V to +2.5 V input range. Using VSS = GND restricts operation to unipolar 0 V to +5 V only. This supply requirement is explicitly defined in the AD7821BQ General Description and Ordering Guide.
What is the purpose of the OFL (overflow) output on the AD7821BQ, and how is it used?
The OFL output on the AD7821BQ is an active-low, non-three-state flag that goes low when the analog input exceeds (VREF(+) – ½ LSB), indicating over-range condition. It is specifically designed to cascade multiple AD7821BQ units - for example, connecting OFL of one device to CS of the next enables automatic 16-bit extended resolution operation. This functionality is confirmed in the Pin Function Descriptions and PRODUCT HIGHLIGHTS sections of the AD7821BQ documentation.
AD7821BQ 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:
- -40°C ~ 85°C
- Supplier Device Package:
- 20-CERDIP
- Mounting Type:
- Through Hole
- Grade:
- -
- Qualification:
- -
AD7821BQ FAQ
1.How can I place an order for AD7821BQ through Aetrix?
Please submit a Request for Quotation (RFQ) for AD7821BQ 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 AD7821BQ reliable?
The price and inventory of AD7821BQ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for AD7821BQ is usually 5 days.
3.What payment methods are accepted for AD7821BQ?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for AD7821BQ transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for AD7821BQ?
AD7821BQ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your AD7821BQ 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 AD7821BQ?
For technical support, including AD7821BQ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your AD7821BQ requirements.
6.How does Aetrix verify that AD7821BQ is sourced from the original manufacturer or authorized distributors?
All AD7821BQ 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 AD7821BQ meets industry standards.
7.What is the process for return or replacement of AD7821BQ?
All AD7821BQ units undergo pre-shipment inspection (PSI). If there is an issue with AD7821BQ, 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 AD7821BQ part is unused and in its original packaging.
Return procedure for AD7821BQ:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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