Analog Devices Inc. AD7870CQ

Overview

AD7870CQ from Analog Devices is a complete monolithic 12-bit successive approximation analog-to-digital converter (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 AD7870CQ datasheet, AD7870CQ pinout, AD7870CQ application, or AD7870CQ equivalent, this page provides verified technical context, real-world interface timing constraints, confirmed analog input behavior, and validated alternative options for industrial signal conditioning and DSP front-end designs.

Technical Context

The AD7870CQ implements a SAR architecture with a fast-settling DAC, high-speed comparator, and internal 3 V temperature-compensated Zener reference. Its track-and-hold acquires signals to 12-bit accuracy in ≤2 μs and supports full-power input frequencies up to 50 kHz.

It features three configurable digital interfaces: 12-bit parallel, two-byte (8-bit) mode, and serial (SCLK/SSTRB/SDATA), all controlled by the 12/8/CLK and HBEN pins. Conversion is initiated either by CONVST rising edge or CS falling edge, with BUSY/INT indicating completion.

Key Specifications

Pinout & Package

The AD7870CQ is housed in a 24-pin, 0.3-inch-wide hermetic dual-in-line package (DIP), designated "CQ" per Analog Devices' ordering guide. Pin functions are electrically identical to the plastic DIP version but qualified for extended temperature and reliability requirements.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7870KN and AD7871KP, the AD7870CQ provides superior long-term stability via hermetic sealing, guaranteed 72 dB SNR across temperature, and tighter track-and-hold acquisition specification-making it the preferred choice for calibrated test gear and safety-critical embedded systems.

Availability

AD7870CQ is available at Aetrix Electronics and suitable for industrial data acquisition, DSP front-end interfacing, test equipment signal capture, and medical instrumentation requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for AD7870CQ 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 AD7870CQ belongs to Analog Devices' legacy LC2MOS precision ADC family, designed specifically for high-accuracy, low-power, self-contained data acquisition in industrial, instrumentation, and embedded control applications.

FAQ

What is the maximum analog input frequency the AD7870CQ can accurately digitize?

The AD7870CQ supports full-power analog input signals up to 50 kHz while maintaining 12-bit accuracy. This is enabled by its track-and-hold amplifier, which acquires input signals to 12-bit precision in ≤2 μs and has a 0.1 dB bandwidth of ~500 kHz. For signals above 50 kHz, amplitude accuracy degrades due to Nyquist limitation at 100 kHz sampling rate. The AD7870CQ datasheet specifies dynamic performance only up to 50 kHz input frequency.

Does the AD7870CQ require external clock components?

No, the AD7870CQ does not require external clock components. It integrates a laser-trimmed internal oscillator that delivers guaranteed conversion times of 6.5–9 μs. Tying the CLK pin to VSS enables this internal clock. An external TTL-compatible clock may be applied to CLK if precise timing control or synchronization with other system clocks is needed-but it is optional, not required. The AD7870CQ achieves full functionality with only ±5 V supplies and decoupling capacitors.

What is the purpose of the 12/8/CLK pin on the AD7870CQ?

The 12/8/CLK pin on the AD7870CQ configures both data format and serial clock behavior. At +5 V, it selects 12-bit parallel output only. At 0 V, it enables byte or serial mode with gated SCLK (stops after transmission). At −5 V, it enables byte or serial mode with continuous SCLK. This single pin eliminates external mode-select logic and allows runtime reconfiguration of the digital interface without hardware changes-critical for flexible test equipment and multi-protocol embedded systems using the AD7870CQ.

Can the AD7870CQ's internal reference be used externally?

Yes, the AD7870CQ's internal 3 V buried Zener reference is available at the REF OUT pin and can supply up to 500 μA to external circuitry. However, the datasheet mandates strict load conditions: maximum 50 pF capacitance and recommended decoupling with a 200 Ω series resistor plus parallel 10 μF tantalum and 0.1 μF ceramic capacitors. Exceeding these limits causes instability and degraded ADC accuracy. For applications requiring 5 V or 10 V references, Figure 7 in the AD7870CQ datasheet shows resistor-divider scaling from REF OUT.

How does the AD7870CQ handle offset and full-scale calibration?

The AD7870CQ supports external offset and full-scale adjustment via dedicated trim pads (not pins), as documented in the "Offset And Full-Scale Adjustment-AD7870" section of its datasheet. Offset must be adjusted before full-scale. In most DSP applications, these errors are digitally corrected post-conversion; however, for metrology-grade systems, analog trimming using precision potentiometers connected to the trim pads ensures optimal linearity. The AD7870CQ's specified ±5 LSB max full-scale error and ±5 LSB max bipolar zero error reflect unadjusted performance at temperature extremes.