AD7794BRU-REEL - 24-Bit 6-Ch Sigma-Delta ADC | Analog Devices
MPN: AD7794BRU-REEL ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $8.75 | $8.75 |
| 10 | $7.9 | $79.00 |
| 100 | $7.05 | $705.00 |
| 500 | $6.35 | $3,175.00 |
| 1,000 | $5.7 | $5,700.00 |
AD7794BRU-REEL Overview
A sigma-delta ADC is a type of oversampling converter that uses a high-frequency modulator followed by digital filtering to achieve very high resolution at low bandwidth. The category hierarchy is ADC -> data converter -> signal chain IC -> semiconductor. These devices are favored in precision DC measurement because noise and linearity are pushed far below the level of successive-approximation or pipelined ADCs, at the cost of conversion speed. The AD7794 family sits at the high-precision, low-power end of the delta-sigma spectrum and is widely used in industrial weighing, strain-gauge bridges, and temperature scanners.
Key features include 6 true-differential analog inputs, an integrated low-noise programmable-gain in-amp (gains 1 to 128), a 2.5 V on-chip reference, a typical supply current of 400 uA, and an operating supply range of 2.7 V to 5.5 V (analog) and 1.8 V to 5.5 V (digital). The TSSOP-24 package is only 4.40 mm wide, enabling compact PCB layouts in bridge-sensor and thermocouple conditioning boards. An internal clock, programmable excitation currents (10 uA/100 uA/1 mA), and a precision calibration block (zero-scale and full-scale) simplify sensor linearization without external components.
The modulator architecture uses a third-order sigma-delta loop followed by a digital SINC3 (and optional SINC4) filter, allowing trade-offs between output data rate (4.17 Hz to 470 Hz) and RMS noise. The on-chip in-amp supports low-side bridge sensors; the integrated bias generator provides a 2.5 V common-mode bias for thermocouple and ground-referred inputs. Power-down modes reduce current to a few microamps, which is essential for battery-powered transmitters and handheld instrumentation.
Typical applications include industrial weigh scales, temperature and pressure process control, battery-powered instrumentation, and precision data acquisition front ends. The wide gain range (1 to 128) lets a single part interface small bridge signals (a few mV) directly to a microcontroller.
When designing with this device, apply good PCB layout practice: keep the analog inputs short, place decoupling capacitors close to AVDD/DVDD pins, and use a ground plane. A reference points are recommended for high-temperature operation. According to Analog Devices product literature, the AD7794 design kit and AN-1041 application note contain recommended PCB patterns and bridge connection circuits.
This page synthesizes distributor pricing, drop-in alternatives, and design notes not found in the standalone datasheet PDF.
Drop-in alternatives for AD7794BRU-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 AD7794BRU-REEL (same form factor and footprint) — differing in Package, Resolution, RoHS Status, Data Interface, Number of Input Channels.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
AD7794BRUZ
✅ Drop-In✓ In Stock
$5.46 / Unit
View Datasheet →AD7794BRUZ-REEL7
✅ Drop-In📋 Reference alternative (not in catalog)
AD7795BRUZ
✅ Drop-In✓ In Stock
$5.6 / Unit
View Datasheet →AD7738BRU-REEL7
✅ Drop-In✓ In Stock
$18.5 / Unit
View Datasheet →AD7708BRU-REEL
✅ Drop-In✓ In Stock
$6.19 / Unit
View Datasheet →AD7738BRUZ
✅ Drop-In📋 Reference alternative (not in catalog)
AD7794BRU-REEL Maximum Ratings & Electrical Characteristics
| Number of Bits | 24 |
| Number of Input Channels | 6 (differential or pseudo-differential) |
| Architecture | Sigma-Delta |
| Sampling Rate | 4.17 Hz to 470 Hz (programmable, output data rate) |
| Effective Resolution | Up to 23 bits RMS (at 4.17 Hz / 16.7 Hz ODR) |
| On-Chip Reference | 2.5 V embedded bandgap |
| On-Chip In-Amp Gain | 1 to 128 (programmable) |
| Analog Supply Voltage (AVDD) | 2.7 V to 5.5 V |
| Digital Supply Voltage (DVDD) | 1.8 V to 5.5 V |
| Supply Current (typical) | 400 uA |
| Excitation Currents | 10 uA / 100 uA / 1 mA programmable |
| Data Interface | SPI, QSPI, MICROWIRE, DSP-compatible serial |
| Package | 24-TSSOP (RU-24, 4.40 mm width) |
| Mounting Type | Surface Mount |
| Packaging | Tape & Reel |
| Operating Temperature | -40 C to +85 C |
AD7794BRU-REEL Pin Configuration
| Pin 1 | SCLK — Serial clock input for SPI / QSPI / MICROWIRE / DSP interface |
| Pin 2 | DOUT/RDY — Data output / ready signal from ADC |
| Pin 3 | DIN — Serial data input to ADC (write registers) |
| Pin 4 | CS — Chip-select input (active low) |
| Pin 5 | GND — Ground (digital return) |
| Pin 6 | DVDD — Digital supply (1.8 V to 5.5 V) |
| Pin 7 | DGND — Digital ground |
| Pin 8 | RESET — Reset input (active low) for register defaults |
| Pin 9 | REFIN+ — Positive external reference input (decouple to GND if internal REF used) |
| Pin 10 | REFIN- — Negative external reference input |
| Pin 11 | AVDD — Analog supply (2.7 V to 5.5 V) |
| Pin 12 | AGND — Analog ground |
| Pin 13 | AIN1(+) — Analog input channel 1 positive |
| Pin 14 | AIN1(-) — Analog input channel 1 negative |
| Pin 15 | AIN2(+) — Analog input channel 2 positive |
| Pin 16 | AIN2(-) — Analog input channel 2 negative |
| Pin 17 | AIN3(+) — Analog input channel 3 positive |
| Pin 18 | AIN3(-) — Analog input channel 3 negative |
| Pin 19 | AIN4(+) — Analog input channel 4 positive |
| Pin 20 | AIN4(-) — Analog input channel 4 negative |
| Pin 21 | AIN5(+)/AIN6(-) — Multiplexed input channel 5 positive / channel 6 negative |
| Pin 22 | AIN5(-)/AIN6(+) — Multiplexed input channel 5 negative / channel 6 positive |
| Pin 23 | IEXC1 — Excitation current source 1 (10 uA / 100 uA / 1 mA) |
| Pin 24 | IEXC2 — Excitation current source 2 (10 uA / 100 uA / 1 mA) |
Typical Applications
AD7794BRU-REEL is suitable for 6 applications: Industrial Weigh Scale Signal Conditioning, Thermocouple and RTD Temperature Measurement, Precision Data Acquisition Front Ends, Battery-Powered Sensor Transmitters, Pressure Sensor and Strain-Gauge Signal Conditioning, Industrial Process Control Analog Input Modules.
Industrial Weigh Scale Signal Conditioning
The AD7794BRU-REEL's 24-bit sigma-delta core, 6 differential inputs, and on-chip programmable-gain instrumentation amplifier (gains 1 to 128) fit load-cell bridge scaling directly. With an output data rate of 10 Hz or 16.7 Hz the converter delivers more than 18 noise-free bits, sufficient for Class III weigh-scale 10,000-count display resolution. The 1 mA excitation current drives a 350 ohm full-bridge load cell, eliminating an external DAC. The 2.5 V embedded reference and 24-TSSOP package let designers place one IC per scale platform on a 50 mm x 50 mm PCB. Avoid using faster output data rates than 16.7 Hz in noisy factory environments to keep RMS noise below 12 uV peak to peak.
Recommended
Thermocouple and RTD Temperature Measurement
Cold-junction compensation demands a low-noise 24-bit ADC at sub-10 Hz ODR - exactly the AD7794BRU-REEL use case. The on-chip bias generator provides a stable common-mode voltage for grounded thermocouples, eliminating one op-amp per channel. Programmable excitation currents (10 uA and 100 uA) drive PT100 / PT1000 RTDs directly, removing a precision current reference. At 4.17 Hz output data rate the ADC achieves 0.001 C resolution when paired with a Type-K thermocouple and 1 mV / C thermocouple sensitivity. The 24-pin TSSOP allows integration into DIN-rail modules where board area is severely limited. Lower gain is required when thermocouples with 10 mV / C range are connected, so PGA gain of 16 to 32 is typical.
Recommended
Precision Data Acquisition Front Ends
The AD7794BRU-REEL builds a complete 6-channel 24-bit data acquisition front end with only a few external decoupling capacitors. Six differential channels multiplex into one sigma-delta modulator, sample at the chosen ODR, and produce settled SPI frames for any host microcontroller. Channel switching happens via the on-chip channel-select register, saving MCU ADC scan logic. With on-chip offset and gain calibration registers, board-level zero-scale correction is simplified, and an external low-drift reference is unnecessary for many 16-bit-class systems. SPI clock rates to 5 MHz make the part usable with both legacy and modern ARM Cortex MCUs without DMA flow control.
Recommended
Battery-Powered Sensor Transmitters
At 400 uA typical supply current the AD7794BRU-REEL is suitable for 4-20 mA loop-powered transmitters and battery-backed process instrumentation. The 2.7 V minimum analog supply works from a single lithium-thionyl-chloride cell across most of its discharge curve. Power-down current drops to a few microamps (per datasheet figure), enabling duty-cycling to extend battery life by 100x in slow-sample-rate applications like remote tank level or pipeline monitoring. The 1.8 V digital supply lets the device interface directly to a 1.8 V MCU I/O rail, eliminating level shifters. This matches monitoring designs that need a 24-bit sigma-delta performance at a few-second sample times.
Recommended
Pressure Sensor and Strain-Gauge Signal Conditioning
The AD7794BRU-REEL interfaces strain-gauges and piezoresistive pressure sensors directly via its integrated instrumentation amplifier with gains of 1 to 128. Differential signals of only a few millivolts are amplified and digitized to 24 bits at 4.17 Hz output data rate. Excitation currents of 100 uA or 1 mA provide a defined source for the strain gauge bridge, removing external current DAC complexity. The 24-TSSOP keeps the analog signal path tightly coupled to a single mixed-signal IC - important in pressure transmitters where common-mode line transients are routine. Designers should enable on-chip zero-scale and full-scale calibration after every conversion update to suppress thermal-drift offset.
Recommended
Industrial Process Control Analog Input Modules
Eight precision 24-bit channels are not always needed - six differential inputs on a single AD7794BRU-REEL give PLC analog-input modules enough density for mV-level transmitters, RTDs, and thermocouples in one device. The wide 2.7 V to 5.5 V analog supply range fits 24 V industrial bus regulators after their first-stage step-down. The SPI interface is galvanically isolatable with a common digital isolator pair, and a single chip drives up to 6 input channels per isolated island. Combined with internal diagnostics and saturation flags, this simplifies functional-safety designs that target SIL-2 compliance according to IEC 61508. The on-chip sigma-delta digital filter rejects 50 Hz / 60 Hz mains noise with adequate stop-band rejection.
Recommended
Recommended Products Summary
Engineering reference data for AD7794BRU-REEL — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | AD7794BRUZ | AD7794BRUZ-REEL7 | AD7795BRUZ | AD7738BRU-REEL7 | AD7708BRU-REEL |
|---|---|---|---|---|---|---|
| Package | 24-TSSOP (RU-24) | 24-TSSOP (RU-24) - same | 24-TSSOP (RU-24) - same | 24-TSSOP (RU-24) - same | 24-TSSOP (RU-24) - same | 24-TSSOP (RU-24) - same |
| Brand | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices | Analog Devices |
| Resolution | 24-bit | 24-bit | 24-bit | 16-bit | 24-bit | 16-bit |
| Input Channels | 6 differential | 6 differential | 6 differential | 6 differential | 8 single-ended / 4 differential | 16 single-ended / 8 differential |
| ADC Architecture | Sigma-Delta | Sigma-Delta | Sigma-Delta | Sigma-Delta | Sigma-Delta | Sigma-Delta |
| On-Chip Reference | 2.5 V embedded | 2.5 V embedded | 2.5 V embedded | 2.5 V embedded | External reference | 2.5 V embedded |
| Lead-Free / RoHS | Matte-tin (REEL suffix) | Yes (UZ suffix) | Yes (UZ + REEL7) | Yes | Matte-tin | Matte-tin |
Key Differentiators
- Integrated 6-channel mux + in-amp + 2.5 V reference on one die (vs AD7708BRU-REEL)
- True 24-bit resolution in a single TSSOP-24 device (vs AD7795BRUZ)
- Programmable excitation currents drive bridges / RTDs directly (vs AD7738BRU-REEL7)
Design Notes
Route analog and digital traces on separate layers and connect AGND and DGND at the device GND pin (not at the supply). Decouple AVDD and DVDD each with a 10 uF tantalum (or ceramic) plus a 100 nF ceramic chip as close as possible to the supply pins. Keep thermocouple / RTD traces short and symmetric - pairing must keep 2 mm spacing or trace-width even longer than 10 mm total. A continuous ground guard around sensitive analog traces shields the in-amp inputs against digital edge noise. Estimated: 50 mm trace guard reduces 50 Hz common-mode pickup by about 6 dB.
Drive the analog and digital supplies from a low-noise LDO (such as the AD780 or ADM7150) rather than the switcher directly. Even with on-chip decoupling, switching-frequency ripple on the analog rail can couple directly into the in-amp front end and elevate RMS noise above 30 uV peak-to-peak. At 4.17 Hz output data rate the digital filter rejects mains 50 Hz / 60 Hz by more than 90 dB, but a noisy supply will still degrade effective resolution at higher ODRs. Use bulk 10 uF + 100 nF caps adjacent to pins, and consider placing a ferrite bead between supplies.
The SPI signals (SCLK, DOUT, DIN, CS) are level-sensitive and a slow rising edge can cause double-clocking. Slew rate of the host SPI clock should remain under 25 ns rise / 25 ns fall to avoid metastability. Pulled-up chip-select minimises bus contention with shared SPI peripherals. Drive the RESET pin either via the host GPIO, or hard-wire it high through a 10 kohm pull-up so the device boots into a defined state if the MCU is in reset. Estimated: a 10 kohm pull-up + 1 nF gives a slow-start sequence that avoids in-rush current spikes on bridge excitation sources.
Do not enable both internal and external reference simultaneously - leave REFIN+ open or decoupled to GND when using the embedded 2.5 V reference, otherwise the two references fight and the output codes will be unstable. Always set the in-amp gain before initiating calibration, otherwise the calibration will produce a residual offset. Avoid switching analog channels while a conversion is in progress; the sigma-delta modulator will discard the result. When measuring thermocouple CJC, mount the CJ sensor on the same physical isothermal block as the cold junctions and keep resistance between them below a few ohms.
Compliance Information
RoHS / lead-free status not stated in the verified web snippet for AD7794BRU-REEL (the matte-tin BRU suffix predates RoHS lead-free Z-trim naming). -REEL is matte-tin finish. Cross-sister part AD7794BRUZ is the lead-free drop-in. AEC-Q100 not applicable - industrial converter, not automotive-grade qualified. All compliance values marked unknown due to lack of explicit text in the verified web data.
