AD7709ARU-REEL - 16-Bit Sigma-Delta ADC w/ Current Sources | Analog Devices
MPN: AD7709ARU-REEL ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $11.5 | $11.50 |
| 10 | $10.35 | $103.50 |
| 100 | $9.2 | $920.00 |
| 500 | $8.05 | $4,025.00 |
| 1,000 | $7.1 | $7,100.00 |
AD7709ARU-REEL Overview
Sigma-Delta ADCs (Σ-Δ ADCs) are a class of analog-to-digital converters that trade raw speed for very high resolution by oversampling the input and shaping quantization noise out of the baseband. They sit above successive-approximation and flash converters in the resolution-vs-speed taxonomy and are the dominant architecture in precision DC, temperature, strain-gauge, and industrial sensor front ends, where update rates from a few Hz to a few kHz suffice and where 16-24 bits of effective resolution can be obtained from inexpensive on-chip digital filtering.
Key features include 16-bit resolution, configurable as 2 fully-differential input channels or 4 pseudo-differential input channels, programmable gain (PGA) from 1 to 128 with input ranges spanning 1.024 V to 6.144 V unipolar and ±1.024 V to ±6.144 V bipolar, three matched software-programmable excitation current sources (typically 10 µA, 200 µA, or 1 mA) for RTD/excitation bridges, simultaneous 50 Hz and 60 Hz mains rejection at the 20 Hz output update rate, an SPI/QSPI/MICROWIRE/DSP-compatible serial interface, and a 2.7 V to 5.25 V analog supply range.
Architecturally the part combines a switched-capacitor Σ-Δ modulator with a digital sinc³ (sin³) low-pass filter and on-chip calibration registers, achieving effective resolution approaching the 16-bit noise floor while rejecting line-frequency interference - the defining requirement of industrial process-control and weigh-scale designs. The current sources and low-side power switches reduce external discrete count by allowing direct sensor excitation and bridge power management without extra transistors.
Typical applications include 4-20 mA industrial process-control loops, weigh scales and load-cell signal conditioning, temperature measurement using RTDs and thermocouples with cold-junction compensation, smart industrial transmitters, flow meters, and battery-cell monitoring where isolated low-bandwidth precision measurement is required.
When designing with this ADC, pay close attention to PCB grounding: separate analog and digital grounds must meet only at the AGND/DGND pin of the AD7709 with a star-ground topology; otherwise the high switching currents in the digital interface couple into the analog front end and degrade effective resolution. Bypass the AVDD and DVDD pins individually with 10 µF + 0.1 µF ceramic pairs placed as close as possible to the package pins.
This page synthesizes distributor inventory, drop-in pin-compatible alternatives, application reference designs, and practical PCB-layout notes not aggregated in the manufacturer datasheet.
Drop-in alternatives for AD7709ARU-REEL — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with AD7709ARU-REEL (same form factor and footprint) — differing in Package, Number of Input Channels, Reference Input, RoHS Status, Architecture.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
AD7709BRU-REEL
✅ Drop-In✓ In Stock
$8.25 / Unit
View Datasheet →AD7709ARUZ-REEL7
✅ Drop-In📋 Reference alternative (not in catalog)
AD7708BRU-REEL
✅ Drop-In✓ In Stock
$6.19 / Unit
View Datasheet →AD7707BRZ-REEL
✅ Drop-In✓ In Stock
$9.4 / Unit
View Datasheet →AD7709ARU-REEL Maximum Ratings & Electrical Characteristics
| Number of Bits | 16 |
| Number of Input Channels | 2 (fully-differential) or 4 (pseudo-differential) |
| Architecture | Sigma-Delta (Σ-Δ) |
| Sampling Rate | 105 sps |
| Data Interface | SPI, QSPI, MICROWIRE, DSP-compatible serial |
| Input Voltage Range (unipolar) | 1.024 V to 6.144 V |
| Input Voltage Range (bipolar) | ±1.024 V to ±6.144 V |
| PGA Gain Range | 1 to 128 |
| Analog Supply Voltage (AVDD) | 2.7 V to 5.25 V |
| Digital Supply Voltage (DVDD) | 2.7 V to 5.25 V |
| Excitation Current Sources | 3 switchable, software-selectable (typ. 10 µA / 200 µA / 1 mA) |
| 50/60 Hz Rejection | Simultaneous, at 20 Hz update rate |
| Output Update Rate | 20 Hz (10 Hz, 25 Hz also programmable) |
| On-chip Calibration | Self-calibration and system calibration registers |
| Digital I/O | 4-bit GPIO port |
| Low-Side Power Switches | Yes, internal FET switches for sensor power gating |
| Operating Temperature Range | -40 °C to +85 °C (industrial) |
| Package | 24-TSSOP (4.40 mm body width) |
| Mounting Type | Surface Mount |
| Packaging | Tape & Reel (TR) |
| RoHS Status | Compliant |
AD7709ARU-REEL Pin Configuration
| Pin 1 | SCLK — Serial clock input |
| Pin 2 | DOUT/RDY — Serial data output / ready indicator (active low) |
| Pin 3 | DIN — Serial data input |
| Pin 4 | CS — Chip select (active low) |
| Pin 5 | RESET — Hardware reset (active low) |
| Pin 6 | GPIO0 — General-purpose digital I/O 0 |
| Pin 7 | GPIO1 — General-purpose digital I/O 1 |
| Pin 8 | GPIO2 — General-purpose digital I/O 2 |
| Pin 9 | GPIO3 — General-purpose digital I/O 3 |
| Pin 10 | DVDD — Digital supply voltage |
| Pin 11 | DGND — Digital ground |
| Pin 12 | AVDD — Analog supply voltage |
| Pin 13 | AGND — Analog ground |
| Pin 14 | REF+ — Positive reference input |
| Pin 15 | REF- — Negative reference input |
| Pin 16 | AIN1(+) — Analog input channel 1, positive |
| Pin 17 | AIN1(-) — Analog input channel 1, negative |
| Pin 18 | AIN2(+) — Analog input channel 2, positive |
| Pin 19 | AIN2(-) — Analog input channel 2, negative |
| Pin 20 | IOUT1 — Excitation current source 1 output |
| Pin 21 | IOUT2 — Excitation current source 2 output |
| Pin 22 | IOUT3 — Excitation current source 3 output |
| Pin 23 | SW1 — Low-side power switch 1 (open drain) |
| Pin 24 | SW2 — Low-side power switch 2 (open drain) |
Typical Applications
AD7709ARU-REEL is suitable for 6 applications: Industrial Weigh Scales / Load Cells, 4-Wire RTD Temperature Measurement, Process-Control Analog Input Modules, Thermocouple Cold-Junction Compensation, Battery Cell Monitoring / Smart Battery Packs, Industrial Transmitter / Loop-Powered Sensor.
Industrial Weigh Scales / Load Cells
The AD7709ARU-REEL is purpose-built for load-cell measurement, where its integrated PGA (gain 1-128) directly amplifies the 10-30 mV full-scale output of a 350-Ω bridge and its three switchable matched excitation current sources (10 µA, 200 µA, 1 mA) supply the bridge for ratiometric measurements. The 20 Hz output update rate with simultaneous 50 Hz and 60 Hz mains rejection eliminates the need for offline line-frequency filtering, while the 16-bit Σ-Δ architecture delivers effective resolution suitable for commercial scale Class III instruments.
Recommended
4-Wire RTD Temperature Measurement
In RTD transmitters the AD7709ARU-REEL drives the RTD with one of its matched excitation current sources (typically 1 mA for 100 Ω Pt100) and measures the resulting voltage with the differential inputs and PGA, automatically cancelling lead-resistance errors via Kelvin sensing. The 16-bit resolution with PGA = 128 covers the Pt100 range from -200 °C to +850 °C, and the on-chip 50/60 Hz rejection simplifies field-transmitter design for global markets operating from 50 Hz or 60 Hz mains.
Recommended
Process-Control Analog Input Modules
For PLC analog input modules the AD7709ARU-REEL multiplexes 4 pseudo-differential channels (or 2 fully-differential) into a single ADC, with on-chip software gain selection eliminating external PGA stages. The 4-bit GPIO port can be used to drive channel-selection relays or status LEDs; the low-side power switches disconnect the sensor during fault conditions to satisfy IEC 61000-4-11 surge-resilience requirements in industrial process control.
Recommended
Thermocouple Cold-Junction Compensation
Coupled with a precision thermocouple-junction RTD channel, the AD7709ARU-REEL delivers low-noise thermocouple digitisation by sampling at 20 Hz to reject environmental mains interference. Use one excitation current source for the cold-junction PT100 and a different channel of the ADC for the thermocouple; the linear ground-referenced inputs and PGA enable direct digitisation of K, J, T, and E thermocouple types with cold-junction compensation computed in software.
Recommended
Battery Cell Monitoring / Smart Battery Packs
In multi-cell smart battery packs the AD7709ARU-REEL monitors each cell voltage through its pseudo-differential inputs and the integrated low-side power switches can be used to balance cells during charge. The 2.7 V to 5.25 V supply range works directly from a single lithium-ion cell, while the 20 Hz update rate is well-suited to tracking slow battery-state-of-charge changes. With PGA = 128, resolution extends to monitor sub-1 mV cell-balance drift.
Recommended
Industrial Transmitter / Loop-Powered Sensor
In 4-20 mA loop-powered industrial transmitters the AD7709ARU-REEL digitises sensor and provides SPI output to the controller; it works from a 3 V LDO post-diode in the loop. The 50/60 Hz rejection is particularly important for loop transmitters installed near motor drives, where EMI is severe. The low quiescent current (a few hundred µA) preserves loop-power budget for the host MCU and HART modem.
Recommended
Recommended Products Summary
Engineering reference data for AD7709ARU-REEL — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | AD7709BRU-REEL | AD7709ARUZ-REEL7 | AD7708BRU-REEL | AD7707BRZ-REEL |
|---|---|---|---|---|---|
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Package | 24-TSSOP (4.40 mm body) | 24-TSSOP - same | 24-TSSOP - same | 24-TSSOP - same | 24-TSSOP - same |
| Resolution | 16-bit | 16-bit | 16-bit | 16-bit | 16-bit |
| Input Channels | 2 fully-diff / 4 pseudo-diff | 2 fully-diff / 4 pseudo-diff | 2 fully-diff / 4 pseudo-diff | 8/16 (depending on mode) | 8/16 (pseudo-diff / pseudo-diff) |
| Integrated PGA | Yes (gain 1-128) | Yes (gain 1-128) | Yes (gain 1-128) | No (requires external PGA) | No (requires external PGA) |
| Excitation Current Sources | 3 switchable | 3 switchable | 3 switchable | None | None |
| Low-side Power Switches | Yes (SW1, SW2) | Yes | Yes | Yes | Yes |
| GPIO Port | 4-bit (GPIO0-3) | 4-bit | 4-bit | Yes | Yes |
| Output Update Rate | 20 Hz (with 50/60 Hz reject) | 20 Hz | 20 Hz | 20 Hz | 20 Hz |
| Supply Voltage | 2.7 V to 5.25 V | 2.7 V to 5.25 V | 2.7 V to 5.25 V | 2.7 V to 5.25 V | 2.7 V to 5.25 V |
Key Differentiators
- Integrates 3 switchable excitation current sources and 2 low-side power switches in the same package (vs AD7708BRU-REEL)
- Integrated programmable gain amplifier (PGA) with gains from 1 to 128 (vs AD7707BRZ-REEL)
- Configuration of 2 fully-differential or 4 pseudo-differential inputs via software (vs AD7705BRU)
Design Notes
Use a star-ground topology with AGND and DGND tied only at the IC's ground pin (pin 11/13). Route the analog and digital grounds as separate planes connecting only at this single point. Place 10 µF bulk + 0.1 µF ceramic bypass capacitors on each of the AVDD and DVDD pins within 2 mm of the package. The low-side excitation current sources return current to AGND; do not allow the IOUT return paths to share traces with digital return currents or 50/60 Hz mains-rejection will degrade.
Always run the self-calibration sequence (CS=1, INITIATE SELF-CAL) after power-up and any gain change to ensure the gain and offset coefficients are updated - otherwise the ADC may return near-zero or saturated readings even when the analog signals are valid. Note that the device exits self-calibration on subsequent init cycles; check the STATUS register ERR and DRDY bits before reading each conversion. Cycling the PGA gain without recalibration is a common cause of returning designs failing EMC conformance tests.
The AD7709 high-resolution conversion is sensitive to high-frequency digital noise on the power rails. Place ferrite beads in series with the AVDD and DVDD supplies at the PCB entry to suppress conducted noise from motors, relays, and switch-mode converters. A π-filter of 10 Ω ferrite + 10 µF + 0.1 µF between AVDD and DVDD typically improves effective resolution by 1-2 LSB in noisy environments. Route the SCLK away from AIN traces, or shield with AGND copper pours.
Compliance Information
The Z-suffix variant (AD7709ARUZ-REEL7) denotes lead-free / RoHS finish; industrial temperature grade -40 °C to +85 °C; Analog Devices is in full compliance with EU Directive 2011/65/EU (RoHS 2).
