Analog Devices Inc. AD7865AS-3

Overview

AD7865AS-3 from Analog Devices is a four-channel, simultaneous-sampling, 14-bit analog-to-digital converter (ADC) with ±2.5 V input range, 2.4 µs conversion time per channel, and integrated track/hold amplifiers. It operates from a single 5 V supply, consumes 115 mW typical power, and delivers 77 dB SNR at 100 kHz input-designed for precision phase-coherent acquisition in motor control and power monitoring systems.

For engineers reviewing the AD7865AS-3 datasheet, AD7865AS-3 pinout, AD7865AS-3 application, or AD7865AS-3 equivalent, key selection considerations include simultaneous sampling integrity, aperture delay matching (≤4 ns), bipolar zero error (±14 LSB max), two's complement output coding, and PQFP-44 package compatibility with industrial temperature range (–40°C to +85°C).

Technical Context

The AD7865AS-3 implements a successive approximation ADC architecture with four independent track/hold amplifiers, enabling true simultaneous sampling across all channels to preserve inter-channel phase relationships. Its internal 2.5 V reference, laser-trimmed oscillator, and hardware/software channel selection logic support flexible sequencing without external timing components.

Conversion is triggered by a rising edge on CONVST, which simultaneously freezes all four track/holds and initiates conversion on selected channels. EOC signals individual channel completion while BUSY indicates full sequence end; data is accessed via 14-bit parallel bus (DB0–DB13) with CS/RD control and supports both reading-between-conversions and reading-after-sequence modes.

Key Specifications

Pinout & Package

The AD7865AS-3 is housed in a 44-lead Plastic Lead Quad Flatpack (PQFP) with 0.8 mm lead pitch and 0.3 in² footprint, optimized for high-density PCB layouts in industrial instrumentation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar simultaneous-sampling ADC applications.

Compared with AD7865AS-3, AD7656ASTZ offers higher resolution and channel count but demands external timing and reference components, increasing design effort; ADS8588HIPM provides greater channel density and resolution but replaces low-latency parallel access with SPI-making AD7865AS-3 optimal for cost-sensitive, phase-critical 4-channel industrial control where integrated features reduce system-level complexity.

Availability

AD7865AS-3 is available at Aetrix Electronics and suitable for AC motor control, industrial power monitoring, and uninterruptible power supply (UPS) systems requiring stable component supply across extended production lifecycles.

Supply support for AD7865AS-3 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 is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA.

The AD7865 product line delivers simultaneous-sampling ADCs for industrial automation and power electronics, emphasizing phase coherence, robustness in harsh environments, and integration of reference, clock, and interface logic to simplify system design.

FAQ

What input voltage range does the AD7865AS-3 support?

The AD7865AS-3 supports a bipolar ±2.5 V analog input range, optimized for signal processing applications requiring symmetric dynamic range around ground. This range is fixed for the -3 variant and differs from the ±10 V/±5 V ranges of the AD7865AS-1 and the 0 V to 2.5 V/0 V to 5 V ranges of the AD7865AS-2. The AD7865AS-3 uses two's complement output coding to represent negative and positive values within this range.

How does the AD7865AS-3 achieve simultaneous sampling across four channels?

The AD7865AS-3 achieves true simultaneous sampling using four independent track/hold amplifiers, each dedicated to one analog input pair (VIN1A/VIN1B through VIN4A/VIN4B). A single rising edge on the CONVST pin places all four amplifiers into hold mode at the exact same instant, freezing their input voltages before conversion begins. This preserves relative phase information between channels-critical for applications like motor control and power analysis where timing alignment is essential. The AD7865AS-3 maintains ≤4 ns aperture delay matching between these amplifiers.

What is the role of the H/S SEL pin on the AD7865AS-3?

The H/S SEL (Hardware/Software Select) pin on the AD7865AS-3 determines the channel selection method: when pulled low, channel enable/disable is controlled by SL1–SL4 hardware pins; when pulled high, channel sequencing is programmed via the channel select register using DB0–DB3 and WR. This dual-mode flexibility allows the AD7865AS-3 to support both fixed-function hardware configurations and dynamic firmware-controlled channel activation-enabling adaptable system architectures without redesigning the PCB layout.

Does the AD7865AS-3 include an internal voltage reference?

Yes, the AD7865AS-3 integrates a 2.5 V ±20 mV internal reference accessible via the VREF pin, eliminating the need for an external reference in most applications. It also supports overdriving with an external 2.5 V ±5% reference for improved stability and accuracy. A 0.1 µF decoupling capacitor is required between VREF and AGND. The internal reference is used for all conversions unless overridden, and its temperature coefficient is 25 ppm/°C typical-ensuring predictable performance across the –40°C to +85°C operating range of the AD7865AS-3.

Can the AD7865AS-3 interface directly with 3 V microcontrollers?

Yes, the AD7865AS-3 supports direct interfacing with 3 V microcontrollers via its VDRIVE pin, which powers the DB0–DB13 data bus, BUSY, EOC, and FRSTDATA outputs. When VDRIVE is supplied with 3 V ±10%, the digital outputs meet 3 V logic thresholds (VOH ≥ 2.4 V, VOL ≤ 0.4 V), allowing seamless connection without level shifters. This feature maintains signal integrity while reducing BOM count and board area-particularly valuable in compact industrial control modules where the AD7865AS-3 serves as the primary acquisition engine.