Analog Devices Inc. AD7485BSTZ

Overview

AD7485BSTZ from Analog Devices is a 14-bit, 1 MSPS successive-approximation ADC with serial interface, internal 2.5 V reference, and 40 MHz full-power bandwidth. It operates from a single 4.75–5.25 V supply, supports flexible digital I/O via VDRIVE (2.7–5.25 V), and delivers ±1 LSB INL, 76.5 dB SINAD at 500 kHz, and 10 µW STANDBY power. It is used in high-speed data acquisition systems requiring precision analog-to-digital conversion with low latency and low power.

For engineers reviewing the AD7485BSTZ datasheet, AD7485BSTZ pinout, AD7485BSTZ application, or AD7485BSTZ equivalent, this page provides verified technical context, real-world timing constraints (e.g., 24-MCLK conversion time, 70 ns track/hold acquisition), confirmed power modes (NAP: 3 mW, STANDBY: 10 µW), and exact package mapping to 48-lead LQFP for layout and thermal design.

Technical Context

The AD7485BSTZ implements an algorithmic SAR architecture using a capacitive DAC and internal comparator, requiring exactly 24 MCLK cycles per conversion. Its track-and-hold supports input frequencies up to 40 MHz with 10 ns aperture delay and 70 ns acquisition time for full-scale step inputs.

It features dual serial interface modes (SMODE-selectable), with SCO derived from MCLK and SDO outputting overrange bit + 14-bit MSB-first straight binary data. Power management is hardware-controlled via dedicated STBY and NAP logic inputs, enabling deterministic transitions between 80 mW normal, 3 mW NAP, and 10 µW STANDBY states.

Key Specifications

Pinout & Package

The AD7485BSTZ is housed in a 48-lead LQFP package (7 mm × 7 mm, 0.5 mm pitch) with exposed pad, rated for –40°C to +85°C operation. Pin functions are validated per Analog Devices AD7485 datasheet Rev. A (2010), including dedicated AGND/DGND separation, dual supply domains (AVDD, DVDD), and mode-control pins (STBY, NAP, SMODE).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 14-bit, 1 MSPS SAR ADC applications.

Compared with AD7485BSTZ, AD7490BRUZ offers higher resolution and channel count but sacrifices VDRIVE flexibility and overrange detection; ADS8326IPW trades throughput and supply range for lower power and simpler interface-neither is pin-compatible, and both require PCB redesign for replacement.

Availability

AD7485BSTZ is available at Aetrix Electronics and suitable for medical ultrasound beamforming, industrial PLC analog input modules, test & measurement oscilloscope front ends, and communications baseband receivers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for AD7485BSTZ 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 AD7485BSTZ belongs to Analog Devices' precision SAR ADC product line, designed specifically for high-speed, low-power data acquisition systems where DC accuracy, AC performance, and flexible digital interfacing are critical in demanding industrial and instrumentation applications.

FAQ

What is the minimum master clock frequency required for AD7485BSTZ operation?

The AD7485BSTZ specifies a minimum master clock (MCLK) frequency of 10 kHz per its timing characteristics table. At this rate, conversion time is 2.4 ms (24 × 100 µs), yielding a maximum throughput of ~416 SPS. For 1 MSPS operation, MCLK must be ≥20.83 MHz (24 cycles per sample). The device supports MCLK from 10 kHz to 25 MHz, enabling scalable performance from low-power monitoring to high-speed acquisition. AD7485BSTZ timing tolerances (e.g., t3, t12) are validated across this full range.

Does AD7485BSTZ support external reference sources, and what are the requirements?

Yes, AD7485BSTZ supports external 2.5 V references applied to the REFIN pin. The reference must be stable within ±1% for specified performance, with ≤1 µA DC leakage and ≤25 pF capacitance. When using an external source, REFSEL must be tied to AGND and a 470 nF capacitor placed between REFIN and AGND. Internal reference remains disabled unless REFSEL is decoupled with 1 nF to AGND. AD7485BSTZ draws ~220 µA from REFIN during conversion, so the source must sustain this transient load without droop.

How does the overrange bit function in AD7485BSTZ serial output?

The AD7485BSTZ serial output frame is 15 bits: the first bit is the overrange (OR) flag, followed by 14 data bits (MSB first) and a trailing zero. OR = 1 indicates VIN < 0 V or VIN > 2.5 V. This bit is latched on the first SCO rising edge after CONVST falling edge and appears before the MSB. It is valid regardless of reference source (internal or external) and requires no additional configuration. AD7485BSTZ does not clamp or saturate-the OR bit enables firmware to detect out-of-range conditions and trigger corrective action without losing data integrity.

What are the PCB layout recommendations specific to AD7485BSTZ for optimal performance?

AD7485BSTZ requires a minimum 3-layer PCB with a solid internal ground plane. Analog and digital sections must be physically separated; AGND and DGND connect at a single point near CBIAS and AVDD decoupling. A 1 nF capacitor must be placed between CBIAS and AGND, and 470 nF between REFOUT and AGND. AVDD/DVDD require local 0.1 µF + 10 µF decoupling. Signal traces (especially VIN, CONVST, SCO) must avoid crossing split planes or running parallel to noisy digital lines. AD7485BSTZ thermal pad must be soldered to ground plane for thermal and electrical integrity.

Can AD7485BSTZ operate with different analog and digital supply voltages?

AD7485BSTZ requires AVDD and DVDD to be within 4.75–5.25 V, but it supports independent digital I/O voltage via VDRIVE (2.7–5.25 V). This allows DVDD = 5 V for core logic while VDRIVE = 3.3 V sets SDO/SCO/SMODE logic levels compatible with 3.3 V controllers. AVDD and DVDD may share a common 5 V rail, but best practice is separate filtering. AD7485BSTZ does not support split analog/digital supply voltages below 4.75 V-both AVDD and DVDD must meet the 5 V ±5% specification.