Analog Devices Inc. AD7485BST

Overview

AD7485BST from Analog Devices is a 14-bit, 1 MSPS successive-approximation analog-to-digital converter (SAR ADC) with serial interface, internal 2.5 V reference, and full-scale overrange indication. It features 40 MHz input bandwidth, ±1 LSB integral nonlinearity, 76.5 dB SINAD at 500 kHz, and operates from a single 4.75–5.25 V supply. It is used in high-speed data acquisition systems requiring precision digitization of analog sensor or signal chain outputs.

For engineers reviewing the AD7485BST datasheet, AD7485BST pinout, AD7485BST application, or AD7485BST equivalent, this page delivers verified technical context, real-world timing and power behavior, package-specific layout guidance, and validated alternative options for industrial instrumentation, medical imaging front-ends, and test equipment design.

Technical Context

The AD7485BST implements an algorithmic SAR architecture using a capacitive DAC and integrated track-and-hold amplifier with 70 ns acquisition time for full-scale step inputs. Its conversion is synchronized to an external master clock (up to 25 MHz), requiring exactly 24 MCLK cycles per sample and delivering data via serial output with MSB-first straight binary coding.

It supports two serial interface modes (selected by SMODE pin): Mode 1 uses CONVST for both conversion initiation and frame synchronization; Mode 2 separates these functions using TFS for framing. Power management includes NAP mode (3 mW, reference active) and STANDBY mode (10 µW, full shutdown), with distinct wake-up times depending on reference source (internal vs. external).

Key Specifications

Pinout & Package

The AD7485BST is housed in a 48-lead LQFP package (7 mm × 7 mm, 0.5 mm pitch) with exposed thermal pad. Pin assignments are validated per Analog Devices AD7485 datasheet Rev. A (2010), including dual ground domains (AGND/DGND), separate analog/digital supplies (AVDD/DVDD), and dedicated reference control pins (REFSEL, REFIN, REFOUT).

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7476AST and ADS8325IPW, the AD7485BST uniquely balances 14-bit accuracy, 1 MSPS speed, integrated reference, and overrange flag in a single 48-lead LQFP-making it optimal for mid-speed instrumentation where feature completeness matters more than absolute resolution or minimal footprint.

Availability

AD7485BST is available at Aetrix Electronics and suitable for industrial PLC analog input modules, portable medical monitors, automated test equipment channels, and ultrasound imaging front-ends requiring stable component supply across extended product lifecycles.

Supply support for AD7485BST 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 AD7485BST belongs to Analog Devices' precision SAR ADC product line, engineered for applications demanding high throughput, low power, and guaranteed DC accuracy without external calibration-especially in portable, industrial, and medical instrumentation.

FAQ

What is the maximum master clock frequency supported by the AD7485BST?

The AD7485BST supports a master clock (MCLK) frequency up to 25 MHz, as specified in the Timing Characteristics table. At this rate, the minimum conversion time is 960 ns (24 × 40 ns), enabling the full 1 MSPS throughput. Operation above 25 MHz violates absolute maximum ratings and may cause timing violations or data corruption. The AD7485BST must be operated within the 10 kHz–25 MHz MCLK range for guaranteed functionality.

Does the AD7485BST require external decoupling capacitors, and if so, where?

Yes, the AD7485BST requires specific external decoupling: a 1 nF capacitor between CBIAS and AGND; a 470 nF capacitor between REFOUT and AGND; a 1 nF capacitor between REFSEL and AGND (when using internal reference) or direct AGND connection (when using external reference); and standard 0.1 µF + 10 µF bulk capacitance on AVDD and DVDD rails. These values are mandatory per the Pin Function Descriptions and Typical Connection Diagram-omission causes degraded PSRR, increased noise, or reference instability in the AD7485BST.

How does the overrange bit function in the AD7485BST serial output?

The AD7485BST serial output delivers 15 bits per frame: the first bit is the overrange indicator, followed by 14 data bits (MSB first) and a trailing zero. The overrange bit is set to logic high whenever the analog input voltage falls outside the 0 V to 2.5 V range-regardless of whether the violation is negative (below 0 V) or positive (above 2.5 V). This bit appears on SDO before any data bits and is sampled on the first SCO rising edge after CONVST falling edge in Mode 1, enabling real-time fault detection without additional circuitry in the AD7485BST system.

Can the AD7485BST operate with an external reference while using the internal reference buffer?

No-the AD7485BST cannot simultaneously use an external reference voltage and its internal reference buffer. When an external 2.5 V reference is applied to REFIN, the internal reference is disabled, and REFSEL must be tied directly to AGND. Conversely, when using the internal reference, REFIN must be left unconnected or grounded, and a 1 nF capacitor must be placed between REFSEL and AGND. The AD7485BST's reference architecture is mutually exclusive: either internal (buffered 2.5 V on REFOUT) or external (driven into REFIN), not both.

What is the wake-up time from STANDBY mode for the AD7485BST when using an external reference?

When the AD7485BST is in STANDBY mode and an external 2.5 V reference remains powered, the wake-up time before initiating a valid conversion is 80 µs. This interval allows internal circuitry-including bias networks and comparator settling-to stabilize after power restoration. Initiating CONVST before this period expires will produce invalid or corrupted conversion results. This 80 µs value is strictly shorter than the 500 ms required when using the internal reference, making external reference essential for low-latency wake-up in battery-powered AD7485BST applications.