Analog Devices Inc. AD7821KRZ

Overview

AD7821KRZ from Analog Devices is a high-speed, 8-bit LC2MOS analog-to-digital converter with integrated track-and-hold, 660 ns conversion time (WR-RD mode), ±1 LSB total unadjusted error over –40°C to +85°C, and dual-supply (±5 V) or single-supply (+5 V) operation for unipolar (0–5 V) or bipolar (±2.5 V) input ranges. It serves as a sampling front-end in real-time data acquisition systems requiring precise digitization of up to 100 kHz analog signals.

For engineers reviewing the AD7821KRZ datasheet, AD7821KRZ pinout, AD7821KRZ application, or AD7821KRZ equivalent, key selection considerations include its half-flash architecture eliminating external clock dependency, ratiometric reference support, 1 MHz maximum sample rate, and microprocessor-compatible control interface (CS, RD, WR, INT, RDY).

Technical Context

The AD7821KRZ implements a half-flash conversion architecture using two cascaded 4-bit flash ADCs - one for MSBs and one for LSBs - with internal DAC feedback and comparator-based sampling. Its sampling instant is precisely defined on the falling edge of WR (WR-RD mode) or RD (RD mode), enabling deterministic timing for DSP applications.

It features fully differential ratiometric reference inputs (VREF(+) and VREF(–)), supports both unipolar and bipolar configurations via VSS pin selection (0 V or –5 V), and delivers dynamic performance including 45 dB SNR and –50 dB THD at 99.85 kHz full-scale sine input with 500 kHz sampling.

Key Specifications

Pinout & Package

AD7821KRZ is housed in a 20-lead SOIC (Small Outline Integrated Circuit) package, RoHS-compliant and surface-mount compatible. Pin 19 (VSS) enables bipolar operation when tied to –5 V; grounding it configures unipolar +5 V operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit, high-speed ADC applications.

Compared with AD7820KN and MAX1112CPE+, the AD7821KRZ uniquely combines sub-microsecond conversion, integrated track-and-hold, bipolar/unipolar configurability, and parallel microprocessor interface - making it optimal for latency-sensitive, mixed-signal embedded systems where timing precision and analog fidelity are non-negotiable.

Availability

AD7821KRZ is available at Aetrix Electronics and suitable for industrial data acquisition, DSP signal sampling, embedded test equipment, and motor control feedback systems requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for AD7821KRZ 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, serving industrial, automotive, communications, and healthcare markets since 1965.

The AD7821KRZ belongs to Analog Devices' legacy high-speed ADC product line, designed specifically for microprocessor-centric data acquisition systems demanding fast, accurate, and easy-to-interface digitization without external timing or support components.

FAQ

What is the maximum analog input frequency the AD7821KRZ can accurately digitize without an external track-and-hold?

The AD7821KRZ can accurately digitize full-scale sine-wave inputs up to 100 kHz without external track-and-hold circuitry, thanks to its inherent sampled-data comparator architecture and 1.6 V/µs slew rate capability. This is confirmed by specifications showing 45 dB SNR and –50 dB THD at 99.85 kHz input under 500 kHz sampling. The AD7821KRZ achieves this through internal timing that samples precisely on the falling edge of WR or RD, ensuring stability during conversion.

Does the AD7821KRZ require an external clock signal to operate?

No, the AD7821KRZ does not require an external clock signal. Its half-flash conversion architecture generates internal timing, eliminating the need for CLK input. Conversion is initiated by WR (in WR-RD mode) or RD (in RD mode), and timing parameters such as tCRD (700 ns max) and tACC1 (240 ns max) are internally controlled. This simplifies system design and reduces noise susceptibility compared to clock-dependent ADCs.

How does the MODE pin affect the AD7821KRZ's interface behavior?

The MODE pin selects between two distinct interface protocols: when MODE = 1 (high), the AD7821KRZ operates in WR-RD mode, using WR to start conversion and RD to read data; when MODE = 0 (low), it enters RD mode, where a single RD strobe initiates and completes conversion. Pin 6 functions as WR input in WR-RD mode and as open-drain RDY output in RD mode - this dual-role pin reduces pin count while supporting both wait-state and non-wait-state microprocessors.

Can the AD7821KRZ operate with a single +5 V supply in bipolar input mode?

No, the AD7821KRZ cannot operate in true bipolar input mode (±2.5 V) with only a single +5 V supply. Bipolar operation requires VSS = –5 V to establish the negative reference rail, as specified in the Absolute Maximum Ratings and General Description. However, the AD7821KRZ supports unipolar 0–5 V input with VSS = GND and +5 V on VDD - this configuration uses only one positive supply and is fully functional for single-ended applications.

What is the purpose of the OFL (overflow) pin on the AD7821KRZ?

The OFL pin on the AD7821KRZ is an active-low, non-three-state output that asserts when the analog input exceeds VREF(+) – ½ LSB, indicating overflow. It is designed for cascading multiple AD7821KRZ devices to achieve higher resolution - for example, two units can be configured so the MSB device's OFL triggers the LSB device's conversion, forming a 12-bit system. Unlike DBx outputs, OFL has no tri-state control and must be externally terminated.