Analog Devices Inc. AD7870LNZ

Overview

AD7870LNZ from Analog Devices is a complete monolithic 12-bit successive approximation ADC with integrated track-and-hold amplifier, laser-trimmed internal clock, and on-chip 3 V buried Zener reference. It delivers 100 kHz sampling rate, 72 dB SNR at 10 kHz input, ±3 V bipolar input range, and 57 ns data access time. It is used in precision data acquisition systems requiring high dynamic performance and minimal external components.

For engineers reviewing the AD7870LNZ datasheet, AD7870LNZ pinout, AD7870LNZ application, or AD7870LNZ equivalent, this page provides verified technical context, real-world interface timing constraints, confirmed analog input scaling behavior, and validated alternative options for industrial and DSP-oriented signal chain design.

Technical Context

The AD7870LNZ implements a SAR architecture with a fast-settling DAC and high-speed comparator, paired with a 2 μs track-and-hold amplifier that acquires full-scale signals to 12-bit accuracy before conversion begins. Its internal 3 V reference is laser-trimmed to ±10 mV and temperature-compensated to ±35 ppm/°C (L/C grade), enabling stable dc accuracy without external trimming.

It supports three digital output formats-parallel 12-bit word, two 8-bit bytes, or serial data-with mode selection controlled by the 12/8/CLK pin. Conversion is initiated either asynchronously via CONVST rising edge or synchronously via CS falling edge, and BUSY/INT provides status feedback with guaranteed 70 ns propagation delay.

Key Specifications

Pinout & Package

AD7870LNZ is housed in a 24-pin, 0.3-inch-wide plastic DIP package (N-24). Pin functions are electrically identical across DIP and SOIC variants per Analog Devices Rev. C datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 12-bit SAR ADC applications.

Compared with AD7870LNZ, AD7871KNZ offers broader temperature tolerance at minor SNR trade-off, while ADS7800U shifts complexity to external reference and supply but gains single-rail compatibility - both require layout review due to differing decoupling and grounding requirements.

Availability

AD7870LNZ is available at Aetrix Electronics and suitable for industrial sensor interfaces, portable test equipment, and embedded data acquisition systems requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for AD7870LNZ 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, founded in 1965 and headquartered in Wilmington, MA.

The AD7870 series belongs to Analog Devices' legacy precision SAR ADC product line, designed specifically for high-accuracy, medium-speed data acquisition in industrial, instrumentation, and DSP-adjacent applications where integration, stability, and ease of use outweigh ultra-high speed or ultra-low power demands.

FAQ

What is the maximum recommended load capacitance on the REF OUT pin of the AD7870LNZ?

The AD7870LNZ REF OUT pin has a maximum recommended load capacitance of 50 pF for stable operation. Exceeding this value may cause reference instability or increased noise. If external buffering or filtering is needed, Analog Devices recommends using a 200 Ω series resistor followed by a parallel 10 μF tantalum and 0.1 μF ceramic capacitor to maintain regulation and suppress switching spikes generated during conversion cycles. This configuration is validated in the AD7870LNZ datasheet Figure 6.

Does the AD7870LNZ support true 12-bit parallel output without byte splitting?

Yes, the AD7870LNZ supports native 12-bit parallel output when the 12/8/CLK pin is held at +5 V. In this mode, DB11 through DB0 function as dedicated data outputs with no multiplexing, and HBEN, SSTRB, SCLK, and SDATA operate solely as inputs or are disabled. The full 12-bit word is available within 57 ns after RD assertion, meeting timing requirements for direct interfacing with 80Cxx and 68000-family microprocessors without glue logic.

Can the AD7870LNZ operate with an external clock, and what is the specified frequency range?

Yes, the AD7870LNZ accepts an external TTL-compatible clock applied to the CLK pin. The specified frequency is 2.5 MHz, yielding a guaranteed maximum conversion time of 8 μs. Operation outside this frequency is not characterized - deviation may affect timing margins, SNR, or integral linearity. When using external clocking, the 12/8/CLK pin must be set to +5 V for parallel mode or 0 V/−5 V for byte/serial modes, and the internal oscillator is automatically disabled.

What is the analog input impedance of the AD7870LNZ, and how does it vary with input voltage?

The AD7870LNZ exhibits a typical analog input impedance of 15 kΩ, measured differentially across VIN and AGND. This value remains stable across the full ±3 V input range and is independent of input signal polarity or amplitude. The impedance is defined by internal scaling resistors (Figure 8 of the datasheet) and does not vary with sampling state - it is present continuously during track and hold phases, making it suitable for direct connection to op-amp buffers or passive RC anti-alias filters without loading error.

Is the AD7870LNZ pin-compatible with other members of the AD7870/AD7875/AD7876 family?

No, the AD7870LNZ is not fully pin-compatible with AD7875 or AD7876 variants. While all share the same 24-pin DIP footprint and identical pin numbering, their analog input structures differ: AD7870LNZ expects ±3 V inputs referenced to AGND, whereas AD7876 requires ±10 V and uses different internal scaling (Figure 9), and AD7875 accepts 0 V to +5 V unipolar inputs (Figure 10). Swapping devices without modifying front-end scaling or reference routing will result in incorrect full-scale code mapping and saturation.