Analog Devices Inc. AD7938BSUZ

Overview

AD7938BSUZ from Analog Devices is a 12-bit, 8-channel, 1.5 MSPS successive approximation register (SAR) ADC with integrated channel sequencer, on-chip 2.5 V reference (±0.2% max @ 25°C), and high-speed parallel interface supporting word/byte modes. It operates from a single 2.7 V to 5.25 V supply and delivers 69 dB SINAD at 50 kHz input frequency in differential mode - used in multichannel data acquisition systems for industrial process monitoring.

For engineers reviewing the AD7938BSUZ datasheet, AD7938BSUZ pinout, AD7938BSUZ application, or AD7938BSUZ equivalent, key selection criteria include its 8-channel sequencer with software-configurable input types (single-ended, pseudo-differential, fully differential), VDRIVE-independent 3 V/5 V interface compatibility, no pipeline delay, and autoshutdown mode consuming ≤2 µA.

Technical Context

The AD7938BSUZ implements a SAR architecture with a differential track-and-hold amplifier capable of handling analog inputs up to 50 MHz full-power bandwidth. Its sequencer supports preprogrammed channel conversion order across all eight VIN0–VIN7 inputs without host intervention.

Conversion is triggered by a falling edge on CONVST, with timing synchronized to CLKIN (up to 25.5 MHz); result availability is signaled via BUSY, and data is read via parallel DB0–DB11 bus under CS/RD control. The on-chip 2.5 V reference has 25 ppm/°C max drift and can be overdriven externally.

Key Specifications

Pinout & Package

AD7938BSUZ is housed in a 32-lead LFCSP (Lead Frame Chip Scale Package) with exposed thermal pad requiring PCB ground vias per Analog Devices' layout guidelines. Pin functions are validated per Figure 2 and Table 6 of Rev. F datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar multichannel SAR ADC applications.

Compared with AD7939BSUZ, AD7938BSUZ provides 2 additional bits and 8 dB higher SINAD at 50 kHz but shares identical packaging, sequencer logic, and power management features; versus AD7606BSTZ, it offers lower latency and simpler parallel interfacing but lacks simultaneous sampling and PGA support - making it optimal for cost- and latency-sensitive sequential acquisition.

Availability

AD7938BSUZ is available at Aetrix Electronics and suitable for industrial process monitoring, motor control feedback, and programmable logic controller (PLC) analog input modules requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for AD7938BSUZ 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 AD7938BSUZ belongs to Analog Devices' precision SAR ADC product line, designed specifically for high-speed, multichannel data acquisition in industrial automation, test equipment, and energy metering where low latency, sequenced sampling, and integrated reference are critical.

FAQ

What is the maximum clock frequency supported by AD7938BSUZ for achieving 1.5 MSPS throughput?

The AD7938BSUZ requires a CLKIN frequency of 25.5 MHz to achieve its rated 1.5 MSPS throughput, as conversion time equals 13 clock cycles plus t2 setup time. Lower CLKIN frequencies reduce throughput proportionally; minimum CLKIN is 700 kHz for specified operation. The AD7938BSUZ datasheet specifies timing parameters t2 through t22 relative to this clock, and all timing margins assume 25 pF load capacitance.

Does AD7938BSUZ support external reference voltage, and what is the acceptable input range?

Yes, AD7938BSUZ supports external reference via the VREFIN/VREFOUT pin, with an operational input range of 0.1 V to VDD. When using an external reference, the internal 2.5 V reference is disabled. The device maintains specified performance only if the external reference voltage remains within ±1% of nominal value - for example, 2.475 V to 2.525 V when targeting 2.5 V. Reference noise must also be considered, as the AD7938BSUZ exhibits 130 µV typical noise in 0.1 Hz to 1 MHz bandwidth.

How does the VDRIVE pin affect interfacing of AD7938BSUZ with a 3.3 V microcontroller?

The VDRIVE pin sets the logic threshold for all parallel interface pins (DB0–DB11, RD, WR, CS, HBEN, BUSY), allowing AD7938BSUZ to interface directly with 3.3 V microcontrollers even when VDD is 5 V. This decoupling eliminates level shifters and ensures reliable communication - for instance, with a 3.3 V ARM Cortex-M4, VDRIVE is tied to 3.3 V while VDD supplies the analog core at 5 V for optimal SNR. The AD7938BSUZ input high voltage (VINH) is guaranteed ≥2.4 V at VDRIVE = 3.3 V.

Can AD7938BSUZ perform fully differential measurements, and how is the input range defined?

Yes, AD7938BSUZ supports fully differential analog inputs on any pair of VINx/VINy channels, with twos complement output coding. The input range is defined as VIN+ and VIN− each spanning VCM ± VREF/2, where VCM is the common-mode voltage (typically VREF/2 = 1.25 V). Alternatively, with VCM = VREF, the range extends to VCM ± VREF, provided VIN+ and VIN− remain within GND to VDD. This flexibility enables accurate measurement of floating or bipolar sensor outputs without external amplification.

What power-saving modes are available in AD7938BSUZ, and what is the lowest quiescent current?

AD7938BSUZ offers three power-saving modes: normal, autostandby, and full/autoshutdown. In full/autoshutdown mode, quiescent current is ≤2 µA - verified across −40°C to +85°C - with all circuitry powered down except wake-up logic. Autostandby reduces current to ~160 µA at 100 kSPS, while normal operational mode draws ≤2.7 mA at 5 V. Power dissipation scales linearly with throughput, enabling dynamic power management in battery-powered DAQ systems using the AD7938BSUZ control register.