Analog Devices Inc. AD7890BR-4

AD7890BR-4 from Analog Devices Inc. Product Summary and IC Specifications (12-Bit DAS, 117K, 24-SOIC)

The AD7890BR-4 from Analog Devices is a robust, high-speed, multi-channel data acquisition system tailored for demanding industrial and embedded measurement tasks. Featuring an integrated 12-bit analog-to-digital converter (ADC) with a conversion time of just 5.9 µs and support for up to eight single-ended analog input channels, the AD7890BR-4 balances performance and integration. With its 0 V to 4.096 V input range, compact 24-lead SOIC package, and bidirectional serial interface, it is ideally suited for multi-channel voltage monitoring, sensor interfacing, and control system applications requiring space-efficient, low-power data collection at rates up to 117 ksps.

Highlighted Features and Technological Improvements of the AD7890BR-4

The AD7890BR-4 brings several significant advancements to single-chip data acquisition. Notably, its Linear Compatible CMOS (LC²MOS) process combines precision analog performance with low-power digital control, resulting in a system that consumes just 50 mW during operation and as little as 75 µW in power-down mode. Each channel can be configured independently, and the device offers distinct signal conditioning paths thanks to separate multiplexer and ADC access—a rare and valuable feature for optimizing filter and timing architectures in multi-channel environments. The device can operate with its on-chip 2.5 V reference or accept an external precision source, supporting tight gain and offset calibration for instrumentation-grade accuracy.

AD7890BR-4 Functional Structure System Diagram and Component Functions

The AD7890BR-4 incorporates several functional blocks:

An eight-channel input multiplexer, selectable via serial commands

A track/hold amplifier, enabling precise sampling and fast acquisition

A high-speed, 12-bit ADC core

On-chip voltage reference circuitry

Flexible bidirectional serial interface ports (SPI-compatible)

User-accessible control register for configuration of channel selection, conversion initiation, and power-down control

This architectural design allows for independent access between the multiplexer and ADC, facilitating integration of external filters and tailored settling times for each application scenario.

Input Specifications, Channel Adaptability, and Signal Interface of the AD7890BR-4

Supporting analog input voltages from 0 V to 4.096 V with a nominal input resistance of 15 kΩ per channel, the AD7890BR-4 is optimized for common sensor and signal standards. Sampling resolutions are mapped as straight binary (natural, LSB increments of 1 mV per code), ensuring straightforward conversion and scaling. Its flexible channel selection mechanism allows rapid updating of the channel address, enabling time-multiplexed measurements with distinct signal paths, and simplifying integration into systems with multiple, heterogeneous voltage sources.

Track-and-Hold Functionality and Signal Processing Features in AD7890BR-4

The integrated track/hold amplifier is engineered for rapid acquisition, sampling input signals up to 58 kHz to 12-bit precision in under 2 µs. Its high input impedance and minimal leakage current (<50 nA) support direct connection from the multiplexer or via external conditioning circuitry. When designing signal conditioning stages between the multiplexer output (MUX OUT) and the ADC input (SHA IN), engineers must ensure the voltage range into SHA IN remains within 0 V to 2.5 V, leveraging the track/hold’s ability to deliver equidistant sampling and minimize aperture uncertainty—critical for systems requiring phase accuracy and low distortion.

Reference Configuration Choices and Their Effect on Precision in AD7890BR-4

AD7890BR-4’s reference input pin provides flexibility: use the internal 2.5 V reference (output available for external circuits, buffered internally) or overdrive with an external precision reference. The internal reference exhibits ±10 mV tolerance at 25°C and a 25 ppm/°C temperature coefficient, suitable for many applications. For tighter gains or integration into system-wide calibration strategies, external devices such as AD680, AD780, or REF-43 can be employed. Reference source accuracy directly affects gain and offset, so selection is a key consideration for precision data acquisition and metrology.

Serial Communication Types and Timing Approaches for the AD7890BR-4

AD7890BR-4 supports two serial interface modes:

Self-clocking (master): The device provides both serial clock and frame synchronization; ideal for DSPs and microcontrollers allowing external clocking.

External clocking (slave): The host provides clock and sync signals, supporting up to 10 MHz clock rates for optimum performance.

Conversion can be started via hardware (CONVST pulse) for precise timing, or via software (control register write), with internal settling pulses managed through the CEXT pin. Timing management—including serial read/write operations relative to the conversion process—is vital for maintaining signal-to-noise ratio and achieving specified dynamic performance, especially at high conversion rates.

Connecting AD7890BR-4 to Microcontroller and DSP Systems Application Examples

The versatile serial port allows seamless connectivity to standard microcontrollers (such as 8xC51 and 68HC11) and DSPs (ADSP-2101, DSP56000, TMS320C25/30). Depending on master/slave configuration, connections are tailored to accommodate differences in word order, frame sync, and clock rate. Sample engineering setups illustrate solutions for monitoring conversion completion, managing simultaneous read/writes, and maximizing throughput—including recommendations for interrupt-driven data handling and serial bus timing constraints.

Antialiasing Filter Application with AD7890BR-4 Integration

One of AD7890BR-4’s key engineering strengths is the ability to insert a single antialiasing filter on the multiplexer output, rather than one per channel. This design, made possible by separate MUX OUT and SHA IN pins, reduces component count and cost while maintaining optimal analog signal integrity. Filter design (typically low-pass) should take account of the settling time imposed by both the AD7890BR-4’s track/hold acquisition and the filter circuit, with the CEXT pin enabling programmable delay to ensure full signal settling before conversion.

Performance Evaluation Linearity, Signal Noise, and Dynamic Behavior of AD7890BR-4

The 12-bit segmented DAC core of the AD7890BR-4 delivers tight linearity: typical relative accuracy is ±¼ LSB, while differential nonlinearity remains within ±½ LSB. Noise performance is excellent, with rms code uncertainty as low as 143 µV (for AD7890-4’s input range) under optimal timing conditions. Dynamic response is characterized by typical SNR values above 71 dB, THD below -85 dB, and an effective resolution of up to 11 bits at 40 kHz input frequency. Performance is highly dependent on conversion timing—engineers must ensure data readout does not overlap sampling and conversion to preserve SNR and avoid code flicker.

Physical Dimensions and Assembly Factors for the AD7890BR-4 Package

AD7890BR-4 is available in a JEDEC-compliant 24-lead SOIC wide-body package, providing compact footprint and straightforward PCB integration. Its mechanical outline supports automated assembly and is suitable for high-density applications. Engineers should be attentive to lead configuration and ensure pin assignments match planned routing and connection schemes.

Alternative and Comparable Options to the AD7890BR-4

For applications requiring alternate input voltage ranges, other variants in the AD7890 series are available:

AD7890-10: Supports ±10 V input range for higher-voltage sensors

AD7890-2: Supports 0 V to 2.5 V input range for lower-voltage domains

In terms of direct alternatives, engineers may also evaluate functionally similar multi-channel, 12-bit serial ADCs such as Analog Devices' AD7862, AD7658, or Texas Instruments' ADS8508, depending on specific channel count, integration, and speed requirements. Selection should factor in timing architecture, reference options, and the ability to support external filtering and settling time customization.

Conclusion

The AD7890BR-4 from Analog Devices presents a powerful solution for modern multi-channel data acquisition tasks, delivering high-speed conversion, integrated signal conditioning, and highly flexible interfacing options in a compact footprint. Its advanced LC²MOS process, multiple serial modes, and user-accessible multiplexer output empower engineers to tailor measurement accuracy, noise performance, and timing to fit complex real-world scenarios. AD7890BR-4's architecture not only simplifies PCB design and system integration but also provides critical capabilities—such as cost-saving antialiasing strategies and external reference support—for projects where measurement fidelity and throughput are paramount. For design teams and procurement engineers seeking reliability, flexibility, and performance, the AD7890BR-4 remains a leading choice in its class.