Analog Devices Inc. AD7655ASTZ

Overview

AD7655ASTZ from Analog Devices is a low-cost, 4-channel, 16-bit, simultaneous-sampling SAR analog-to-digital converter with dual track-and-hold amplifiers, 500 kSPS throughput in normal mode, 0 V to 5 V analog input range, and parallel/serial 3 V/5 V interface - used in multichannel industrial data acquisition systems requiring precise phase-coherent sampling across two differential pairs.

For engineers reviewing the AD7655ASTZ datasheet, AD7655ASTZ pinout, AD7655ASTZ application, or AD7655ASTZ equivalent, key selection criteria include simultaneous dual-channel sampling capability, impulse-mode power scaling (2.6 mW at 10 kSPS), no pipeline delay, ±6 LSB integral linearity, and pin compatibility with AD7654 for drop-in migration in motor control and power monitoring designs.

Technical Context

The AD7655ASTZ implements a charge redistribution SAR architecture with internal error correction and dual independent track-and-hold circuits enabling true simultaneous sampling of two differential input pairs (INA1/INB1 or INA2/INB2) selected via A0. Its conversion logic supports both normal (500 kSPS) and impulse (444 kSPS) modes, where power scales linearly with throughput.

It integrates dual 16-bit conversion paths, an internal conversion clock, and flexible digital interfacing - supporting parallel 16-bit bus operation or SPI/QSPI/MICROWIRE-compatible serial protocols with master/slave configurations, byte-swapping, and configurable SYNC/SCLK polarity via dedicated control pins (INVSYNC, INVSCLK, EXT/INT).

Key Specifications

Pinout & Package

AD7655ASTZ is packaged in a 48-lead LQFP (Leadless Quad Flat Package) with exposed pad grounded for thermal management. Pin functions are validated per Analog Devices Rev. E datasheet Figure 4 and Table 6.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7654ASTZ, the AD7655ASTZ delivers 2× throughput and tighter linearity at modest power increase; versus AD7656ASTZ, it offers optimal cost/performance balance for 4-channel systems without over-spec'ing channel count or power consumption.

Availability

AD7655ASTZ is available at Aetrix Electronics and suitable for AC motor control, 3-phase power monitoring, and industrial data acquisition requiring stable component supply, long-term lifecycle support, and traceable sourcing from authorized channels.

Supply support for AD7655ASTZ 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. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA, with design centers worldwide and ISO 9001-certified manufacturing.

The AD7655ASTZ belongs to Analog Devices' PulSAR® family of precision SAR ADCs, engineered specifically for industrial automation, energy metering, and motor control applications demanding simultaneous sampling, low latency, and robust noise immunity.

FAQ

What is the maximum sampling rate of the AD7655ASTZ and under what conditions?

The AD7655ASTZ achieves a maximum throughput of 500 kSPS in normal mode with AVDD = DVDD = 5 V, OVDD ≥ 2.7 V, and VREF = 2.5 V. This rate corresponds to a 2 µs complete conversion cycle for both channels. In impulse mode, the rate is 444 kSPS (2.25 µs cycle), with power scaled proportionally - delivering 114 mW typical at that speed. Both modes operate across the full −40°C to +85°C industrial temperature range.

Does the AD7655ASTZ require an external reference voltage, and what are the acceptable ranges?

Yes, the AD7655ASTZ requires an external reference voltage applied to the REF pin. The specified range is 2.3 V to AVDD/2 (i.e., up to 2.5 V when AVDD = 5 V). It draws up to 180 µA from the reference source at 500 kSPS. The device also supports independent reference inputs REFA and REFB for each channel pair, referenced to REFGND, enabling ratiometric or isolated measurements - a capability confirmed in the General Description and Table 2 of the Rev. E datasheet.

How does the A0 pin control input channel selection in the AD7655ASTZ?

The A0 pin selects which pair of differential inputs is simultaneously sampled: when A0 is logic LOW, the AD7655ASTZ samples INA1 and INB1; when A0 is HIGH, it samples INA2 and INB2. This 2:1 multiplexer front-end enables full 4-channel operation using only two track-and-hold amplifiers - a core architectural feature documented in the Functional Block Diagram, General Description, and Pin Function Descriptions (Table 6, Pin 3) of the AD7655ASTZ datasheet.

Can the AD7655ASTZ interface directly with a 3 V microcontroller, and how is level compatibility achieved?

Yes, the AD7655ASTZ supports direct interfacing with 3 V logic systems via its OVDD pin, which powers the digital I/O interface independently. When OVDD is set to 3 V, all digital outputs (D[0:15], BUSY, EOC, etc.) swing between 0 V and 3 V, and inputs (SER/PAR, A0, RD, CS, etc.) accept 0 V to 3 V logic levels - verified in Table 2 (Digital Inputs/Outputs) and Pin Function Descriptions (Pin 18). This eliminates level-shifters in mixed-voltage systems.

What is the significance of the IMPULSE pin on the AD7655ASTZ, and how does it affect power consumption?

The IMPULSE pin enables a low-power operating mode where the AD7655ASTZ dynamically scales its power consumption with throughput. When IMPULSE = HIGH, power drops from 120 mW at 500 kSPS to 114 mW at 444 kSPS and further to 2.6 mW at 10 kSPS - a >45× reduction. This behavior is intrinsic to the internal clock and bias circuitry, as confirmed in the Product Highlights, Specifications table (Power Dissipation), and Modes of Operation section of the AD7655ASTZ Rev. E datasheet.