Analog Devices Inc. AD7939BCPZ

Overview

AD7939BCPZ from Analog Devices is a 10-bit, 8-channel, 1.5 MSPS successive approximation register (SAR) ADC with integrated channel sequencer, on-chip 2.5 V reference (±0.2% @ 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, or fully differential analog inputs for industrial data acquisition systems.

For engineers reviewing the AD7939BCPZ datasheet, AD7939BCPZ pinout, AD7939BCPZ application, or AD7939BCPZ equivalent, key selection considerations include its 10-bit resolution with ±0.5 LSB INL, 61 dB SINAD at 50 kHz, software-configurable input modes, VDRIVE-independent 3 V/5 V interface compatibility, and LFCSP-32 package with exposed thermal pad.

Technical Context

The AD7939BCPZ implements a SAR architecture with no pipeline delay, enabling deterministic conversion timing of t₂ + 13 × t_CLKIN. Its track-and-hold amplifier supports full-power bandwidth up to 50 MHz and handles 125 ns max acquisition time for full-scale step inputs.

Channel sequencing is managed via an on-chip control register supporting preprogrammed scan orders across all eight analog inputs (VIN0–VIN7). Input configuration-single-ended, pseudo-differential (7- or 4-channel), or fully differential-is selected in real time via register bits, with straight binary or two's complement output coding.

Key Specifications

Pinout & Package

AD7939BCPZ is housed in a 32-lead LFCSP (CP-32-7) package with exposed thermal pad requiring PCB vias to ground plane per Analog Devices layout guidelines.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7939BCPZ, AD7938BCPZ delivers higher resolution at identical speed and footprint, while ADS8688IPWR trades throughput for resolution and adds PGA functionality - neither is pin-compatible, but both address adjacent design requirements in multichannel data acquisition.

Availability

AD7939BCPZ is available at Aetrix Electronics and suitable for industrial PLC analog input modules, medical patient monitors, automotive battery management systems, and portable test equipment requiring stable component supply and long-term manufacturability.

Supply support for AD7939BCPZ 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, with R&D and manufacturing operations worldwide.

The AD793x family targets high-speed, low-power, multichannel data acquisition in space-constrained industrial and medical systems - emphasizing integration (on-chip reference, sequencer), flexible interfacing (VDRIVE), and robust noise immunity.

FAQ

What is the maximum clock frequency supported by AD7939BCPZ for 1.5 MSPS operation?

The AD7939BCPZ requires a CLKIN frequency of 25.5 MHz to achieve its rated 1.5 MSPS throughput. This is derived from its fixed 13-clock-cycle conversion time plus setup timing (t₂). Operation at lower CLKIN frequencies reduces throughput linearly; the minimum specified CLKIN is 700 kHz for functional operation, though performance specifications apply only at or above 25.5 MHz. The AD7939BCPZ does not support variable oversampling or decimation modes.

Can AD7939BCPZ operate with an external reference voltage, and what is the acceptable range?

Yes, AD7939BCPZ supports external reference input via the VREFIN/VREFOUT pin. The acceptable external reference range is 0.1 V to VDD, as confirmed in the datasheet's Reference section. When using an external reference, the internal 2.5 V reference is disabled. For optimal performance, the external reference must meet noise (<130 µV rms, 0.1 Hz–1 MHz) and impedance (<10 Ω) requirements specified for the internal reference, and the pin must be decoupled with a 470 nF capacitor to AGND.

How does the VDRIVE pin affect interfacing with a 3.3 V microcontroller while VDD is 5 V?

The VDRIVE pin sets the logic threshold for all parallel interface pins (DB0–DB11, RD, WR, CS, etc.), independent of VDD. When VDRIVE = 3.3 V and VDD = 5 V, the AD7939BCPZ digital interface operates at 3.3 V logic levels, allowing direct connection to a 3.3 V microcontroller without level shifters. VDRIVE must remain within −0.3 V to VDD + 0.3 V, so 3.3 V is fully compliant with 5 V VDD. This feature is explicitly designed into the AD7939BCPZ to simplify mixed-voltage system design.

What is the purpose of the HBEN pin, and how does it behave in byte versus word mode?

The DB8/HBEN pin serves dual functions depending on the W/B (Word/Byte) pin state. When W/B = high (word mode), DB8/HBEN acts as Data Bit 8. When W/B = low (byte mode), it becomes the High-Byte Enable (HBEN) control: when HBEN = low, DB0–DB7 carry the low byte; when HBEN = high, DB0–DB3 carry the top 4 bits of the high byte, and DB4–DB6 contain the channel ID. This mode is documented in Table 10 of the AD7939BCPZ datasheet and enables flexible data access without requiring full 12-bit bus width.

Does AD7939BCPZ support simultaneous sampling across all 8 channels?

No, AD7939BCPZ does not support true simultaneous sampling. It uses a single SAR core with an 8-channel multiplexer and sequencer, meaning channels are sampled sequentially - one after another - with deterministic inter-channel delay determined by conversion time (≈13 × t_CLKIN) and t_QUIET. While the sequencer automates channel selection, the architecture is inherently multiplexed, not parallel-sampled. For simultaneous sampling, a device with multiple independent ADC cores (e.g., AD7606 family) would be required.