Analog Devices Inc. AD1555AP

Overview

AD1555AP from Analog Devices is a 24-bit sigma-delta modulator with integrated programmable gain amplifier (PGA), designed for high-precision, low-frequency measurement systems. It delivers ≥116 dB dynamic range at 1 kHz output word rate with PGA gain of 1, features fourth-order continuous-time modulator architecture, supports five PGA gains (1/2.5/8.5/34/128), and operates from ±5 V analog supplies with 5 V digital supply. It targets seismic data acquisition where ultra-low noise and robust input handling are critical.

For engineers reviewing the AD1555AP datasheet, AD1555AP pinout, AD1555AP application, or AD1555AP equivalent, key selection considerations include its guaranteed minimum dynamic range across gain settings (Table Ia), jitter tolerance (300 ps), differential input impedance (140 MΩ), common-mode rejection (≥91 dB), and compatibility with AD1556 digital filter for full 24-bit ADC implementation.

Technical Context

The AD1555AP implements a fourth-order continuous-time sigma-delta modulator that eliminates need for external antialias filtering. Its fully differential PGA accepts inputs via AIN(±) or TIN(±), with gain selected by CB0–CB4 control pins - enabling precise signal conditioning before modulation.

It outputs a ones-density bitstream synchronized to MCLK (256 kHz nominal), with modulator error flagged via MFLG and overvoltage detection embedded. The device uses separate analog grounds (AGND1/AGND2/AGND3) and digital ground (DGND) to maintain >116 dB dynamic range under specified conditions.

Key Specifications

Pinout & Package

AD1555AP is housed in a 28-lead Plastic Lead Chip Carrier (PLCC) package (P-28A), with exposed thermal pad not connected internally. Pin layout follows standard PLCC orientation with Pin 1 identifier corner.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar sigma-delta modulator applications.

Compared with AD1555BP and ADS1282IPWR, the AD1555AP provides optimal trade-off between guaranteed dynamic range at 0°C–85°C, discrete modulator+filter flexibility, and proven robustness in high-EMI seismic instrumentation - without requiring layout changes or firmware rework.

Availability

AD1555AP is available at Aetrix Electronics and suitable for seismic data acquisition, chromatography instrumentation, automatic test equipment, high-accuracy sensor signal conditioning, and industrial process monitoring requiring stable component supply across extended production lifecycles.

Supply support for AD1555AP 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.

The AD1555AP belongs to Analog Devices' precision sigma-delta modulator product line, engineered specifically for ultra-low-noise, high-dynamic-range measurement of sub-kHz analog signals in instrumentation and scientific applications.

FAQ

What is the guaranteed minimum dynamic range of the AD1555AP at 1 kHz output word rate with PGA gain of 1?

The AD1555AP guarantees a minimum dynamic range of 116 dB at 1 kHz output word rate with PGA gain of 1, as specified in Table Ia of the datasheet. This value is guaranteed by design and applies across the full 0°C to +85°C operating temperature range. The AD1555AP achieves this performance using its fourth-order continuous-time sigma-delta modulator architecture and low-noise PGA front-end.

Can the AD1555AP operate without the AD1556 digital filter?

Yes, the AD1555AP can operate independently as a standalone sigma-delta modulator, outputting a 256 kSPS ones-density bitstream on MDATA. However, it does not produce a usable digital word without external decimation filtering. The AD1555AP is designed to interface with the AD1556 for full 24-bit conversion, but users may implement custom FIR or CIC filters. The AD1555AP itself contains no on-chip digital filter.

What are the absolute maximum ratings for the analog supply pins of the AD1555AP?

The AD1555AP absolute maximum ratings specify +VA to –VA ≤ 14 V, +VA to AGND ≤ +7 V, and –VA to AGND ≥ –7 V. Exceeding these limits risks permanent damage. The recommended operating range is ±5 V ±5% (i.e., +VA = 4.75–5.25 V, –VA = –5.25 to –4.75 V). These ratings are defined in the Absolute Maximum Ratings table on page 8 of the AD1555/AD1556 Rev. B datasheet.

How is the reference voltage applied to the AD1555AP, and what is the recommended source?

The AD1555AP accepts a 3.0 V ±10 mV reference at the REFIN pin (Pin 25), which is internally divided to set the modulator full-scale range. Analog Devices recommends the AD780BR as the reference source. External 22 µF tantalum capacitors must be placed from REFCAP1 (Pin 23) to AGND3 (Pin 22) and from REFCAP2 (Pin 24) to AGND2 (Pin 27) to stabilize the reference path and ensure specified dynamic performance of the AD1555AP.

Does the AD1555AP support differential input configurations, and what is the common-mode rejection ratio?

Yes, the AD1555AP supports true differential input via AIN(+) and AIN(–) or TIN(+) and TIN(–), with common-mode rejection ratio (CMRR) of ≥91 dB at PGA gain of 1 and fIN = 200 Hz. CMRR improves with higher PGA gains - reaching 108 dB at PGA = 128. This performance is measured with ±2.25 V common-mode voltage and is critical for rejecting noise in industrial sensor interfaces using the AD1555AP.