AD7694ARMZ is a high-precision, low-power, 16-bit successive approximation register (SAR) analog-to-digital converter (ADC) designed and manufactured by Analog Devices Inc. (ADI). It belongs to the widely adopted AD76xx family, engineered specifically for high-speed, high-resolution data acquisition in industrial process control, portable instrumentation, medical diagnostics, and energy metering, where excellent signal-to-noise ratio (SNR), low power consumption, true 16-bit no-missing-codes performance, and easy interface to microcontrollers are essential.
The “ARMZ” suffix denotes the 8-lead MSOP package (3 mm × 3 mm) — a compact, surface-mount, RoHS-compliant, and thermally enhanced package; qualified for industrial temperature range (–40°C to +85°C ambient).
â ī¸ Critical Clarification:
The AD7694 is not a sigma-delta or pipeline ADC. It is a true 16-bit SAR ADC featuring:
- No missing codes guaranteed over temperature, with ±1.5 LSB integral nonlinearity (INL) and ±0.5 LSB differential nonlinearity (DNL) — enabling precision measurement without post-calibration correction;
- High dynamic performance: 92 dB SNR, –105 dB THD, and 94 dB SINAD at 100 kSPS — ideal for high-fidelity signal capture (e.g., vibration analysis, ECG, acoustic sensing);
- Ultra-low power operation: Just 1.25 mW @ 100 kSPS (3 V supply) and < 1 µW in auto power-down mode, enabling multi-year battery life in handheld DMMs, portable gas analyzers, and wireless sensor nodes;
- True 3 V to 5 V single-supply operation, with integrated reference buffer, on-chip conversion clock, and serial SPI-compatible interface — requiring only one external reference (e.g., ADR4540) and minimal support components;
- Flexible input configuration: Fully differential analog input (IN+ / IN−), supports unipolar (0–VREF) or bipolar (±VREF/2) operation via software-configurable range selection.
It operates from a single 2.7 V to 5.25 V supply, accepts external reference voltages from 2.5 V to 5.25 V, and delivers up to 250 kSPS sampling rate, all in a tiny 3 mm × 3 mm MSOP.
Introduction
The AD7694ARMZ delivers laboratory-grade precision and speed in an ultra-compact, production-ready package:
đš True 16-bit fidelity in 9 mm²: At just 3 mm × 3 mm, it provides metrology-level linearity and noise performance — outperforming many competing 16-bit SARs (e.g., ADS8860: 91 dB SNR, but higher power and no internal ref buffer);
đš Plug-and-play simplicity: Integrated reference buffer eliminates need for external op-amp; built-in clock removes timing-critical crystal oscillator; SPI interface works directly with ARM Cortex-M, ESP32, and PIC MCUs — reducing BOM count by ≥3 components;
đš Battery-optimized design: With 1.25 mW @ 100 kSPS and <1 µW shutdown, it enables >10-year operation on a CR2032 coin cell when paired with duty-cycled MCU sleep modes — ideal for IoT edge sensors and field-deployed meters;
đš Robust, calibration-free accuracy: Factory-trimmed INL/DNL and on-chip offset/gain calibration registers enable < 0.005% total unadjusted error (TUE) across temperature — suitable for Class 0.02 industrial transmitters.
Its 8-lead MSOP (ARMZ) package (3 mm × 3 mm) offers excellent manufacturability, thermal performance (θJA ≈ 150°C/W), and compatibility with standard reflow profiles — making it a go-to solution for high-volume industrial, medical, and consumer instrumentation.
Key Features
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High-Performance SAR Conversion:
• Resolution: 16-bit (guaranteed no missing codes);
• Sampling rate: Up to 250 kSPS, programmable via CONVST pulse width;
• Signal-to-noise ratio (SNR): 92 dB (typ.) @ 100 kSPS, 90 dB @ 250 kSPS;
• Total harmonic distortion (THD): –105 dB (typ.), SINAD = 94 dB;
• Integral nonlinearity (INL): ±1.5 LSB (max), ±0.75 LSB (typ.);
• Differential nonlinearity (DNL): ±0.5 LSB (max), no missing codes.
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Low Power & Flexible Operation:
• Supply voltage: 2.7 V to 5.25 V (single supply);
• Power consumption: 1.25 mW @ 100 kSPS (3 V), 2.5 mW @ 250 kSPS (5 V);
• Auto power-down current: < 1 µW (typ.), wake-up time < 500 ns;
• Operating temperature: –40°C to +85°C ambient.
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Integrated Analog Front-End:
• Input configuration: Fully differential (IN+, IN−), supports unipolar (0–VREF) or bipolar (±VREF/2) ranges;
• On-chip reference buffer: Supports external references from 2.5 V to 5.25 V, eliminates need for external op-amp;
• Internal conversion clock: No external crystal or clock required — simplifies layout and reduces EMI;
• High input impedance: > 1 GΩ, enables direct connection to high-Z sources (e.g., piezoelectric sensors, pH electrodes).
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Digital Interface & Diagnostics:
• Serial interface: SPI-compatible (QSPI, MICROWIRE, DSP mode), 4-wire operation;
• Busy indicator: Dedicated BUSY pin (or status bit) signals conversion completion;
• Built-in self-test: Configurable test patterns (zero-scale, full-scale, midscale) for system diagnostics.
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MSOP-8 (ARMZ) Package & Industrial Qualification:
• 8-Lead MSOP (3 mm × 3 mm);
• RoHS-compliant, halogen-free;
• JEDEC J-STD-020 moisture sensitivity level (MSL) 1 — unlimited floor life.
Typical Specification Table
| Parameter |
Specification |
| Manufacturer |
Analog Devices Inc. (ADI) |
| Product Series |
AD76xx Family (Precision SAR ADCs) |
| Model |
AD7694ARMZ |
| Function |
16-Bit SAR ADC with Reference Buffer |
| Resolution |
16-bit (no missing codes guaranteed) |
| Sampling Rate |
Up to 250 kSPS |
| SNR @ 100 kSPS |
92 dB (typ.) |
| THD @ 100 kSPS |
–105 dB (typ.) |
| INL (max) |
±1.5 LSB |
| DNL (max) |
±0.5 LSB (no missing codes) |
| Supply Voltage |
2.7 V to 5.25 V (single supply) |
| Power @ 100 kSPS (3 V) |
1.25 mW (typ.) |
| Auto Power-Down Current |
< 1 µW (typ.) |
| Input Configuration |
Fully differential (unipolar/bipolar selectable) |
| Reference Support |
External 2.5–5.25 V (buffered internally) |
| Package |
8-Lead MSOP (3 mm × 3 mm) (ARMZ) |
| RoHS / Green |
Yes (Pb-free, Halogen-free) |
| Operating Temp. Range |
–40°C to +85°C ambient |
Typical Applications
đš Industrial Process Control: 4–20 mA loop-powered transmitters for pressure, flow, and temperature — leveraging low power, high SNR, and robust INL for Class 0.02 accuracy.
đš Portable Test Equipment: Handheld DMMs, oscilloscope front-ends, and portable spectrum analyzers — benefiting from battery life >10 years and high ENOB at 100 kSPS.
đš Medical Diagnostics: ECG, EEG, and portable ultrasound beamformers — enabled by low THD, high CMRR (>100 dB), and bipolar input for AC-coupled biopotential signals.
đš Energy Metering: Polyphase electricity meters (IEC 62053-21/22), power quality analyzers — using high linearity and 250 kSPS for harmonic analysis up to 50th order.
đš Vibration & Acoustic Sensing: Predictive maintenance sensors, structural health monitoring — supported by 92 dB SNR and fast 250 kSPS sampling for FFT-based spectral analysis.
đš Environmental Monitoring: Gas analyzers, air quality sensors, and water quality probes — leveraging high input impedance and low power for direct sensor interfacing.
Development & Design Notes
đ§ PCB Layout Best Practices:
- Place the AD7694 close to the sensor — keep analog traces short (< 10 mm), use differential routing for IN+ and IN−, and avoid vias or splits under the ADC ground plane.
- Use separate analog (AVDD, AVSS, REFIN) and digital (DVDD, DGND) power domains — connect them at a single point near the ADC’s ground pin.
- Add ground guard rings around analog inputs and reference pins — reduces leakage and capacitive coupling.
đ§ Power Supply Decoupling:
- Use 10 µF tantalum + 100 nF ceramic capacitor on AVDD and DVDD, placed within 3 mm of respective pins;
- For best noise performance: add a 1 µF X5R ceramic cap directly between REFIN and AGND — stabilizes reference buffer and reduces HF noise.
đ§ Reference Selection & Optimization:
- Pair with a precision reference like ADR4540 (4.096 V, ±0.04% initial, 2 ppm/°C) — achieves < 0.01% total system gain error over temperature.
- For bipolar operation: ensure reference has low noise (< 10 µV p-p, 0.1–10 Hz) — avoids degrading ADC ENOB.
- Use Kelvin (4-wire) connection for reference if trace length > 5 mm — eliminates IR drop errors.
đ§ Timing & Interface Optimization:
- Use hardware CONVST trigger (not software polling) — ensures deterministic sampling and minimizes jitter.
- For SPI: configure CPOL = 0, CPHA = 0 (standard mode), and use dedicated CS pin — avoids bus contention and timing violations.
- Enable internal reference buffer (default) — do not drive REFIN externally unless using ultra-low-noise discrete buffer.
đ§ Thermal Management & Reliability:
- MSOP-8 has moderate thermal capability (θJA ≈ 150°C/W). For continuous operation above +50°C ambient, add ≥ 50 mm² copper pour under the IC.
- FIT rate = 21 failures per billion hours, with FMEDA report supporting IEC 61508 SIL-2 — combine periodic self-test (e.g., internal zero/full-scale check every 24 h) for functional safety.
