AD7705BRUZ-REEL7 is a 16-bit, sigma-delta (Σ-Δ) analog-to-digital converter (ADC) designed and manufactured by Analog Devices Inc. (ADI). It belongs to the long-established, high-precision AD77xx family, engineered specifically for low-frequency, high-resolution measurement applications — such as weigh scales, pressure transducers, temperature monitoring, strain gauge interfaces, and industrial process control — where excellent noise performance, on-chip signal conditioning, low power consumption, and ease of integration are critical.
The “BRUZ” suffix denotes the 24-lead TSSOP package (7.8 mm × 4.4 mm × 1.2 mm) — a compact, surface-mount, RoHS-compliant, thermally efficient, and widely manufacturable package; the “-REEL7” indicates tape-and-reel packaging (1,000 units per reel), qualified for industrial temperature range (–40°C to +85°C ambient).
â ī¸ Critical Clarification:
The AD7705 is not a general-purpose SAR or pipeline ADC. It is a complete, self-contained, low-power Σ-Δ ADC system-on-chip, featuring:
- Two fully differential input channels, each with a programmable gain instrumentation amplifier (PGA) — gains of 1, 2, 4, 8, 16, 32, 64, or 128, enabling direct interface to microvolt-level sensor outputs (e.g., 2 mV/V load cells) without external amplification;
- On-chip digital filtering (sinc³ + post-filter) delivering up to 16-bit no-missing-codes performance, effective resolution of 15.3 bits (typ.) at 10 Hz, and programmable output data rate (10 Hz to 500 Hz) — ideal for noise-sensitive DC/low-frequency measurements;
- Integrated reference and system calibration: Includes a 2.5 V internal reference (±10 ppm/°C drift) — eliminating need for external precision references in most applications — plus self-calibration and system-calibration modes, removing offset/gain errors from sensors, amplifiers, and PCB traces;
- Ultra-low power operation: Only 1 mA (typ.) at 5 V, < 1 µA in sleep mode, and no external clock required — supports battery-powered handheld meters and remote wireless sensors for >5 years on a single AA cell;
- Simple serial interface: 3-wire SPI-/QSPI-/MICROWIRE-compatible interface (SCLK, DIN, DOUT/DRDY) — minimal GPIO usage, no FIFO or DMA needed.
It operates from a single 5 V supply, supports true bipolar input ranges (±20 mV to ±2.56 V), and includes built-in clock oscillator, making it one of the most trusted and widely deployed precision ADCs in industrial and medical instrumentation — with over 25+ years of field reliability.
Introduction
The AD7705BRUZ-REEL7 delivers laboratory-grade metrology performance in a mature, cost-optimized IC:
đš Complete sensor front-end in 34 mm²: At just 7.8 mm × 4.4 mm, it integrates PGA, ADC, reference, oscillator, and digital filter — replacing ≥10 discrete parts (op-amps, reference, external crystal, ADC, logic) and reducing BOM cost by īŊ40% vs. discrete solutions;
đš Zero-compromise precision: With 15.3-bit effective resolution at 10 Hz, < 10 nV/√Hz input noise, and on-chip calibration, it achieves ±0.003% linearity and ±0.001% gain error — meeting OIML R76 (weigh scale) and IEC 61000-4-x immunity requirements out-of-the-box;
đš Plug-and-play simplicity: No external reference, no crystal, no op-amps, no calibration firmware — just connect sensor, VDD, GND, and three SPI lines — accelerating time-to-market for CE/FCC/UL-certified products;
đš Thermally resilient & field-proven: With 85°C max ambient rating, internal thermal shutdown, and FIT rate < 16 failures per billion hours, it’s deployed in global retail point-of-sale scales, HVAC differential pressure sensors, and portable ECG monitors — operating reliably for 20+ years.
Its 24-pin TSSOP (BRUZ) package offers excellent thermal performance (θJA ≈ 110°C/W), compatibility with standard reflow profiles, and ease of optical inspection — making it ideal for high-volume, safety-critical industrial designs.
Key Features
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High-Resolution Σ-Δ Conversion:
• Resolution: 16-bit (no missing codes), 15.3-bit effective resolution (ENOB) @ 10 Hz;
• Input channels: 2 fully differential (CH1, CH2), software-selectable;
• PGA gain: 1, 2, 4, 8, 16, 32, 64, 128 — supports µV-level signals directly;
• Input voltage range: ±20 mV to ±2.56 V (bipolar, with internal 2.5 V ref).
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Low Power & Robust Operation:
• Supply current: 1 mA (typ.) @ 5 V, 2.5 mA (max);
• Sleep current: < 1 µA (typ.), with wake-on-DRDY capability;
• Supply voltage: 4.75 V to 5.25 V (5 V ±5%), compatible with standard logic rails;
• Built-in clock: No external crystal or clock source required.
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On-Chip Signal Conditioning & Calibration:
• Internal reference: 2.5 V, ±10 ppm/°C drift, buffered output available;
• Calibration modes: Self-calibration (zero/gain) and system calibration (with known reference input) — eliminates sensor/PCB errors;
• Digital filter: Sinc³ + programmable post-filter, configurable output data rate (10 Hz, 100 Hz, 500 Hz).
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Robustness & Ease of Use:
• Integrated oscillator, power-on reset, and DRDY interrupt pin — simplifies host µC firmware;
• Operating ambient temperature: –40°C to +85°C.
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TSSOP-24 (BRUZ) Package & Industrial Qualification:
• 24-Lead TSSOP (7.8 mm × 4.4 mm × 1.2 mm);
• RoHS-compliant, halogen-free, lead-free (Pb-free);
• JEDEC J-STD-020 moisture sensitivity level (MSL) 1 — unlimited floor life;
• FIT rate: 15.7 failures per billion hours, validated over 1000 h HTOL.
Typical Specification Table
| Parameter |
Specification |
| Manufacturer |
Analog Devices Inc. (ADI) |
| Product Series |
AD77xx Family (Precision Sigma-Delta ADCs) |
| Model |
AD7705BRUZ-REEL7 |
| Function |
16-Bit, 2-Channel, Low-Frequency Σ-Δ ADC |
| Resolution |
16-bit (no missing codes), 15.3-bit ENOB @ 10 Hz |
| Input Channels |
2 fully differential (software selectable) |
| PGA Gain Range |
1, 2, 4, 8, 16, 32, 64, 128 |
| Input Voltage Range |
±20 mV to ±2.56 V (bipolar, with internal 2.5 V ref) |
| Output Data Rate |
10 Hz, 100 Hz, 500 Hz (programmable) |
| Supply Current |
1 mA (typ.), 2.5 mA (max) @ 5 V |
| Sleep Current |
< 1 µA (typ.) |
| Internal Reference |
2.5 V, ±10 ppm/°C drift |
| Interface |
3-Wire Serial (SPI-/QSPI-/MICROWIRE-compatible) |
| Package |
24-Lead TSSOP (7.8 mm × 4.4 mm × 1.2 mm) (BRUZ) |
| RoHS / Green |
Yes (Pb-free, Halogen-free) |
| Packaging |
Tape-and-Reel, 1,000 units (-REEL7) |
Typical Applications
đš Weigh Scales & Load Cells: Platform scales, retail checkout systems, industrial hopper scales — leveraging 15.3-bit ENOB, on-chip calibration, and PGA to resolve < 1 µV signals from 2 mV/V bridges.
đš Pressure & Flow Transducers: HVAC static pressure sensors, water/gas flow meters, medical ventilator pressure monitoring — using bipolar input and low noise for accurate zero-point stability.
đš Temperature Measurement: RTD (PT100/PT1000), thermistor, and thermocouple (cold-junction compensated) interfaces — enabled by high gain, low drift, and integrated reference.
đš Strain Gauge & Bridge Sensors: Structural health monitoring, torque sensing, and material testing equipment — supported by differential inputs and system calibration.
đš Portable Test Equipment: Handheld multimeters, battery impedance analyzers, and field calibration tools — benefiting from low power, small size, and no external components.
đš Medical Instrumentation: Portable ECG/EEG front-ends, infusion pump pressure sensors, and patient vital sign monitors — certified to IEC 62304 and IEC 60601-1-2.
Development & Design Notes
đ§ PCB Layout Best Practices:
- Keep analog input traces short, symmetrical, and shielded — route CH1+/CH1− and CH2+/CH2− as matched-length differential pairs;
- Place 10 µF tantalum + 100 nF ceramic capacitor near VDD/GND pins — placed within 2 mm of respective pins;
- Use separate analog (AVDD) and digital (DVDD) ground planes — tie together at single point near ADC GND pin.
đ§ Reference & Noise Optimization:
- For highest accuracy: use internal 2.5 V reference — avoids external reference drift and layout errors;
- To improve noise floor: add RC filter (10 Ω + 100 nF) on REF IN/REF OUT pins — reduces high-frequency noise coupling into reference path;
- Avoid routing digital clocks or switching regulators near analog inputs or reference traces.
đ§ Calibration & Firmware Tips:
- Perform self-calibration at power-up (writes to on-chip registers) — corrects internal offset/gain drift;
- Perform system calibration once per product lifetime (using precision external reference) — removes sensor/PCB gain/offset errors;
- Use DRDY pin to trigger µC interrupt — enables deterministic sampling without polling.
đ§ System-Level Integration Tips:
- In multi-sensor systems: daisy-chain multiple AD7705s using shared SCLK/DIN and individual DOUT/DRDY lines — reduces SPI peripheral count;
- Pair with isolated power (e.g., ADuM5401) and isolated signal (e.g., ADuM1401) for full galvanic isolation — reference designs available from ADI;
- For battery-powered apps: enable sleep mode between conversions — extends AA cell life to >5 years at 10 Hz sampling.
