AD7870JPZ

Overview

The AD7870JPZ is a complete monolithic 12-bit analog-to-digital converter (ADC) manufactured by Analog Devices Inc. It features an internal track-and-hold amplifier with a maximum acquisition time of 2 μs and a successive approximation ADC core with a conversion time of 8 μs. The device operates from ±5 V power supplies and accepts a single-ended analog input voltage range of ±3 V. It incorporates a laser-trimmed internal clock and a 3 V buried Zener reference, eliminating the need for external timing components or reference sources. Data output is available via parallel, byte, or serial interfaces, supporting data access times as fast as 57 ns. The component is housed in a 28-pin plastic leaded chip carrier (PLCC) package.

Feature Summary

• Integrates a 12-bit SAR ADC with a high-speed track-and-hold amplifier and a factory-trimmed internal clock oscillator.
• Includes an on-chip temperature-compensated 3 V buried Zener reference with sufficient drive capability for external loads.
• Offers versatile digital interfacing options including 12-bit parallel, two-byte, and serial data formats controlled by logic inputs.
• Provides dynamic performance specifications such as signal-to-noise ratio and harmonic distortion suitable for DSP applications.

Applications

• Data acquisition systems requiring fast microprocessor interfacing
• Digital signal processing (DSP) front-ends
• Portable battery-powered instrumentation

Procurement Notes

Verify the specific suffix JPZ corresponds to the commercial temperature range (0°C to +70°C) and the PLCC-28 package configuration. Confirm that the ordering part number matches the exact pinout and electrical specifications defined in the official Analog Devices datasheet for the AD7870 series before finalizing procurement decisions.

Selection Notes

Select the AD7870JPZ when a ±3 V input range is required alongside a complete 12-bit sampling solution. Ensure the system design accommodates ±5 V dual power supplies. Consider the internal 3 V reference limitations if higher external reference voltages are necessary, as scaling circuits may be required for other variants in the family.

Part Context

The AD7870 is part of the AD7870/AD7875/AD7876 family of 12-bit sampling ADCs. While sharing the same core architecture and interface logic, the AD7870 is distinguished by its bipolar ±3 V analog input range. Other family members offer different input ranges, such as unipolar 0 V to +5 V or wider bipolar ±10 V ranges, allowing for flexible selection based on signal conditioning requirements.

Replacement Considerations

Direct functional replacements within the same manufacturer's portfolio include the AD7875 and AD7876, though these differ in analog input voltage ranges. Verify pin compatibility and software register configurations when substituting between these family members to ensure seamless integration into existing designs.

FAQ

How is the internal clock configured?

The internal laser-trimmed clock is enabled by tying the CLK pin to VSS. An external TTL-compatible clock can be applied to this pin to override the internal oscillator if required.

What is the function of the 12/8/CLK pin?

This three-function input defines the data format and serial clock behavior. A high level selects 12-bit parallel output, while low or negative levels enable byte or serial data modes with corresponding serial clock gating.

Can the internal reference be used externally?

Yes, the REF OUT pin provides the internal 3 V reference. It can supply up to 500 μA to an external load but requires decoupling with a series resistor and capacitors to suppress voltage spikes during conversion.