Analog Devices Inc. AD7938BCP

Overview

AD7938BCP from Analog Devices is a 12-bit, 8-channel, 1.5 MSPS successive approximation register (SAR) analog-to-digital converter with integrated channel sequencer, on-chip 2.5 V reference (±0.2% max @ 25°C), and parallel word/byte interface. It operates from a single 2.7 V to 5.25 V supply, consumes 6 mW at 3 V/1.5 MSPS, and supports single-ended, pseudo-differential, and fully differential input configurations for industrial data acquisition systems.

For engineers reviewing the AD7938BCP datasheet, AD7938BCP pinout, AD7938BCP application, or AD7938BCP equivalent, key selection considerations include its 12-bit resolution, 8-channel sequencer with software-configurable input modes, no-pipeline-delay conversion architecture, VDRIVE-enabled 3 V/5 V processor interfacing, and LFCSP-32 package compatibility with high-density PCB layouts.

Technical Context

The AD7938BCP implements a SAR ADC core with a wide-bandwidth differential track-and-hold amplifier supporting up to 50 MHz full-power bandwidth. Its sequencer enables preprogrammed, automatic cycling across eight analog inputs without host intervention, and internal control registers configure input range (0–VREF or 0–2×VREF), output coding (straight binary or two's complement), and power modes (normal, autostandby, full shutdown).

Conversion is triggered by a falling edge on CONVST, with BUSY signaling completion; data is read via parallel interface using CS, RD, and WR with byte/word mode selectable via W/B. The VDRIVE pin decouples logic I/O voltage (2.7–5.25 V) from analog supply (VDD), enabling direct interfacing to mixed-voltage microprocessor buses.

Key Specifications

Pinout & Package

The AD7938BCP is housed in a 32-lead Lead Frame Chip Scale Package (LFCSP) with exposed pad, requiring connection of the EPAD to PCB ground plane via multiple vias for optimal thermal and electrical performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7939BCP, AD7938BCP delivers 2 extra bits of resolution and 2 dB higher SINAD at 50 kHz, justifying its use in closed-loop control; versus AD7682BCP, it trades resolution for double the channel count, 6× higher throughput, and integrated sequencer-making it superior for real-time multi-sensor systems with tight timing constraints.

Availability

AD7938BCP is available at Aetrix Electronics and suitable for industrial automation, motor control, portable instrumentation, and medical sensor signal acquisition requiring stable component supply and long-term production continuity.

Supply support for AD7938BCP 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 AD7938 is part of Analog Devices' precision SAR ADC product line, engineered for high-speed, low-power, multichannel data acquisition in space-constrained industrial and medical systems where deterministic latency and integrated features reduce system complexity.

FAQ

What is the maximum sampling rate supported by the AD7938BCP?

The AD7938BCP supports a maximum throughput rate of 1.5 MSPS, achieved with a 25.5 MHz master clock input and fixed 13-clock-cycle conversion time. This rate is guaranteed across the full operating temperature range (−40°C to +85°C) and supply voltage range (2.7 V to 5.25 V). The AD7938BCP maintains this performance without pipeline delay, making it suitable for time-critical applications requiring deterministic latency.

Does the AD7938BCP require an external reference voltage?

No, the AD7938BCP includes an accurate on-chip 2.5 V reference with ±0.2% maximum error at 25°C and 25 ppm/°C temperature coefficient, sufficient for most industrial applications. However, the VREFIN/VREFOUT pin can be overdriven with an external reference from 0.1 V to VDD if tighter accuracy or custom full-scale range is required. The AD7938BCP operates correctly with either internal or external reference without hardware modification.

How does the channel sequencer in the AD7938BCP operate?

The AD7938BCP's hardware sequencer automatically cycles through up to eight analog input channels in a user-programmed order stored in its shadow register. Once enabled, it performs conversions without host CPU intervention, reducing firmware overhead. Sequencing is triggered by CONVST edges or can run continuously; channel selection, input mode (single-ended/differential), and range are configured per channel via the control register. This feature is integral to the AD7938BCP's architecture and requires no external logic.

What is the purpose of the VDRIVE pin on the AD7938BCP?

The VDRIVE pin sets the logic voltage level for all digital interface pins (CS, RD, WR, DB0–DB11), independent of the analog supply VDD. This allows the AD7938BCP to interface directly with 3 V or 5 V microprocessors even when VDD is at a different voltage-eliminating level shifters. VDRIVE must be between 2.7 V and 5.25 V and within −0.3 V to VDD + 0.3 V. This dual-supply flexibility is a defined feature of the AD7938BCP interface design.

Can the AD7938BCP operate in low-power modes, and how are they controlled?

Yes, the AD7938BCP supports three power modes: normal, autostandby, and full shutdown. Autostandby reduces current to 160 µA at 100 kSPS; full shutdown draws ≤2 µA. These modes are controlled via the on-chip control register-no external hardware is needed. The AD7938BCP exits shutdown automatically on a rising edge of CONVST, enabling rapid wake-up for burst-mode acquisition. Power state transitions are fully specified in the AD7938BCP datasheet timing tables.