Analog Devices Inc. DC845A

Overview

DC845A from Analog Devices (formerly Linear Technology) is a demonstration board for the LTC2444 8-channel/16-input, 24-bit No Latency ΔΣ ADC with selectable speed/resolution, internal oscillator, and SPI interface. It supports up to 4kHz multiplexing rate, 2µV_RMS noise at 1.76kHz, and simultaneous 50Hz/60Hz rejection - enabling high-precision industrial data acquisition and direct temperature measurement.

For engineers reviewing the DC845A datasheet, DC845A pinout, DC845A application, or DC845A equivalent, this page delivers verified hardware configuration details, supported ADC variants (LTC2444/LTC2445), real-world timing behavior, and design-critical interface constraints including BUSY-driven data capture, EXT-controlled SCK mode selection, and COM-referenced single-ended channel routing.

Technical Context

The DC845A implements the LTC2444 in a fully populated, production-ready QFN-38 layout with decoupling, reference buffering, thermocouple interface, and jumper-selectable input configurations. It routes all 38 pins-including dedicated CH0–CH7, COM, REF+, REF−, BUSY, EXT, FO, and 4-wire SPI signals-to accessible test points and headers.

It supports both internal oscillator (FO = GND/VCC) and external clock modes, enables no-latency 1X and one-cycle-latency 2X speed modes via SDI control, and validates guaranteed modulator stability across full input/reference common-mode ranges (GND to VCC) without lock-up under any condition.

Key Specifications

Availability

DC845A is available at Aetrix Electronics and suitable for industrial data loggers, precision weight scales, auto-ranging DVMs, and thermocouple-based temperature monitoring systems requiring stable component supply and validated reference designs.

Supply support for DC845A includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices, Inc. (ADI) acquired Linear Technology in 2017 and maintains full technical and supply chain support for legacy Linear products including the LTC244x family.

The DC845A belongs to ADI's portfolio of evaluation boards for high-resolution delta-sigma ADCs, designed specifically to accelerate validation of multi-channel, low-noise, high-stability measurement systems in industrial and instrumentation applications.

FAQ

What is the primary function of the DC845A evaluation board?

The DC845A evaluation board is a fully assembled and tested hardware platform for evaluating the LTC2444 24-bit No Latency ΔΣ ADC. It provides immediate access to all critical signals - including CH0–CH7, COM, REF+, REF−, BUSY, EXT, FO, and 4-wire SPI - enabling rapid prototyping of high-precision, multi-channel data acquisition systems without custom PCB development. The DC845A validates real-world timing, noise, and calibration behavior of the LTC2444 under controlled conditions.

Which ADC variants are supported by the DC845A?

The DC845A is specifically configured for the LTC2444 (8-differential/16-single-ended inputs, QFN-38 UHF package). While the board's schematic and layout align with the LTC2444 pinout and functional requirements, it does not support the LTC2445/LTC2449 due to their additional MUXOUT/ADCIN pins (Pins 24–27), nor the LTC2448/LTC2449 16-channel variants, as those require different channel routing and COM handling. The DC845A documentation and silkscreen explicitly identify LTC2444 compatibility.

How does the DC845A handle input configuration for single-ended vs differential measurements?

The DC845A uses the COM pin (Pin 7) as the common negative input for all single-ended configurations, allowing any of CH0–CH7 to be measured relative to COM. For differential measurements, users select complementary channel pairs (e.g., CH0+/CH1−) directly through the LTC2444's internal multiplexer. Jumper options on the board enable flexible reference setup (REF+ and REF−), and the COM net is routed with low-impedance grounding to minimize noise coupling - ensuring accurate implementation of both pseudo-differential unipolar and fully differential input topologies as defined in the LTC2444 datasheet.

What power supply and decoupling requirements does the DC845A implement for the LTC2444?

The DC845A supplies the LTC2444 with a regulated 5V rail and implements the exact decoupling specified in the LTC2444 datasheet: a 10µF tantalum capacitor in parallel with a 0.1µF ceramic capacitor placed directly at Pin 28 (VCC), plus dedicated ground connections for all seven GND pins (Pins 1, 4, 5, 6, 31, 32, 33). The exposed thermal pad (Pin 39) is soldered to the PCB ground plane. This layout ensures stable operation across the full –40°C to 85°C temperature range and meets the <5µV offset and 0.0005% INL specifications under real-world PCB parasitics.

Can the DC845A be used to verify simultaneous 50Hz/60Hz rejection performance?

Yes - the DC845A supports simultaneous 50Hz/60Hz rejection at the 6.9Hz output rate, as confirmed by the LTC2444 datasheet's RMS noise vs speed plot (Figure 2440 TA01b) and the board's validated reference design. When configured for 6.9Hz operation (OSR = 32768, 1X mode), the DC845A delivers 200nV_RMS noise with inherent notch filtering at both 50Hz and 60Hz, eliminating the need for external digital post-processing. This capability is demonstrated using the onboard thermocouple interface and calibrated low-frequency signal sources, making the DC845A ideal for AC-coupled industrial sensor applications.