Analog Devices Inc. AD7856ANZ

Overview

AD7856ANZ from Analog Devices is a 14-bit, 285 kSPS successive approximation register (SAR) analog-to-digital converter (ADC) operating from a single 5 V supply. It features eight single-ended or four pseudo-differential analog inputs, on-chip reference (4.096 V), self- and system calibration, and SPI/QSPI/μP-compatible serial interface - used in portable instrumentation, medical data acquisition, and high-speed modem front-ends.

For engineers reviewing the AD7856ANZ datasheet, AD7856ANZ pinout, AD7856ANZ application, or AD7856ANZ equivalent, key selection considerations include its 14-bit resolution with ±2 LSB INL, 78 dB SNR at 10 kHz input, 3.5 µs conversion time (A-grade), flexible power-down modes (2.5 mW typ), and 24-pin PDIP package compatibility.

Technical Context

The AD7856ANZ implements a charge redistribution SAR architecture with integrated track-and-hold (500 ns acquisition), internal 4.096 V reference, and programmable channel configuration via a 14-bit control register. Its serial interface supports Mode 1 (two-wire DIN/DOUT sharing) and Mode 2 (three-wire), with SYNC framing and SCLK up to 6 MHz (A-grade).

Calibration is managed through dedicated CAL pin and control register bits (CALMD, CALSLT1/0, STCAL), enabling automatic power-up self-calibration, system offset/gain calibration, and retention of coefficients in sleep mode. Power management uses SLEEP pin combined with PMGT1/PMGT0 bits to achieve full or partial power-down states.

Key Specifications

Pinout & Package

AD7856ANZ is housed in a 24-lead, 0.3-inch-wide plastic dual in-line package (PDIP), designated N-24 per Analog Devices' ordering guide. Pin spacing is 0.1 inch (2.54 mm), compatible with standard through-hole PCB layouts and socketing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7856ARZ, AD7856ANZ provides identical electrical performance in a through-hole package ideal for prototyping and low-volume industrial assemblies, while ADS8320U trades integrated calibration and reference for higher resolution at reduced speed and increased system complexity.

Availability

AD7856ANZ is available at Aetrix Electronics and suitable for portable medical instrumentation, battery-powered data loggers, and industrial process control systems requiring stable component supply, long-lifecycle availability, and traceable sourcing from authorized channels.

Supply support for AD7856ANZ 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 Wilmington, MA.

The AD7856ANZ belongs to Analog Devices' precision SAR ADC product line, designed specifically for applications demanding high resolution, low power, and integrated calibration in portable and industrial measurement systems.

FAQ

What is the maximum sampling rate supported by the AD7856ANZ?

The AD7856ANZ achieves a maximum throughput rate of 285 kSPS in its A-grade version, corresponding to a 3.5 µs conversion time. This is achieved using a 6 MHz master clock (CLKIN) and requires reading data during conversion (Interface Mode 2) to sustain full speed. The K-grade version operates at 102 kSPS with a 4 MHz clock. Both versions maintain 14-bit accuracy and ±2 LSB INL across their respective speed ranges. The AD7856ANZ's track-and-hold acquisition time is 500 ns, enabling accurate sampling of signals up to 10 MHz full-power bandwidth.

Does the AD7856ANZ require an external reference voltage?

No, the AD7856ANZ does not require an external reference voltage because it integrates a precise 4.096 V reference with 20 ppm/°C tempco, accessible at the REFIN/REFOUT pin. However, the device supports external reference override: applying a stable 1.2 V to V_DD reference to REFIN/REFOUT allows user-defined scaling. When using the internal reference, external capacitors (0.1 µF + 470 nF on CREF1, 0.01 µF on CREF2) must be connected to AGND for DAC stability. The AD7856ANZ's reference output remains functional even in sleep mode if calibration data retention is required.

How does the AD7856ANZ handle channel selection and input configuration?

The AD7856ANZ supports eight single-ended inputs (AIN1–AIN8 referenced to AGND) or four pseudo-differential pairs (e.g., AIN1–AIN2, AIN3–AIN4) via software configuration. Channel selection and mode are controlled by three bits (CH2–CH0) and the SGL/DIFF bit in the 14-bit control register. Default power-up state selects AIN1(+) and AIN2(–) in pseudo-differential mode. No hardware jumpers or strapping pins are needed - all configuration is performed over the serial interface. The AD7856ANZ's input structure ensures AIN(+) never falls below AIN(–), preventing invalid differential conditions that could corrupt conversion results.

What power management options are available on the AD7856ANZ?

The AD7856ANZ offers three distinct power management states: normal operation (60 mW typ), automatic power-down after conversion (2.5 mW typ), and SLEEP-mode power-down (5 µA max with external clock off). These are controlled jointly by the SLEEP pin and two power management bits (PMGT1/PMGT0) in the control register. Full power-down disables the internal reference and analog circuitry while retaining calibration memory; partial power-down maintains reference bias for faster wake-up. The AD7856ANZ's power-down sequencing is transparent to the serial interface, allowing seamless resumption of conversions after wake-up without reinitialization.

Can the AD7856ANZ perform system-level calibration, and how is it initiated?

Yes, the AD7856ANZ supports both self-calibration (on-chip DAC and reference) and system calibration (correcting external sensor and signal chain errors). System calibration is initiated by setting CALMD = 1 and selecting CALSLT1/CALSLT0 = 11 in the control register, then asserting the CAL pin. It requires applying precise zero-scale (system offset) and full-scale (system gain) voltages to the selected input channel. The AD7856ANZ stores resulting correction coefficients in on-chip calibration registers and applies them automatically during conversion. This capability enables end-equipment manufacturers to achieve <0.1% total measurement uncertainty without factory-trimmed components, and the AD7856ANZ retains these coefficients across sleep cycles.