AD7878BQ

Overview

The AD7878BQ is a complete 12-bit, 100 kHz sampling Analog-to-Digital Converter (ADC) featuring an integrated DSP interface. It utilizes Linear Compatible CMOS (LC2MOS) technology and operates on dual ±5 V supplies with a typical power dissipation of 60 mW. The device includes an on-chip track/hold amplifier with a 2 μs acquisition time, a 3 V zener reference, and an 8-word FIFO memory to reduce software overhead. Key performance metrics include a Signal-to-Noise Ratio (SNR) of 72 dB at a 10 kHz input frequency and a maximum data access time of 57 ns. The analog input range is bipolar ±3 V.

Feature Summary

• Integrated 8-word First-In, First-Out (FIFO) memory reduces microprocessor servicing overhead by allowing multiple samples to be digitized before data retrieval.
• Versatile DSP interface with fast data access times compatible with high-speed processors such as the ADSP-2100 and TMS320 series.
• On-chip status and control register provides real-time monitoring of FIFO word count, empty/full states, and sample overrange conditions.
• Extended read/write capability allows bus disabling during conversion start to prevent transients from affecting the track/hold amplifier.

Applications

• Digital Signal Processing systems
• Speech recognition and synthesis hardware
• Spectrum analysis equipment
• High-speed modem implementations
• DSP-based servo control loops

Procurement Notes

Verify the specific grade suffix 'BQ' corresponds to the -25°C to +85°C industrial temperature range and Q-28 Cerdip package when sourcing. Confirm that the ordering part number matches the required SNR specification of 72 dB min. Ensure compatibility with the ±5 V supply requirements and TTL-compatible logic levels for the digital interface connections.

Selection Notes

Select the AD7878BQ for applications requiring a complete ADC solution with minimal external components and direct interfacing to DSPs. The 72 dB SNR and 57 ns access time make it suitable for high-performance signal processing. Consider the B-grade version for industrial temperature environments (-25°C to +85°C). Verify that the system clock can support the required 8 MHz operation for optimal dynamic performance.

Part Context

The AD7878 belongs to Analog Devices' LC2MOS family of complete A/D converters designed for high-speed data acquisition. The 'B' suffix denotes the industrial temperature grade (-25°C to +85°C), while 'Q' indicates the hermetic ceramic DIP (Cerdip) package style. This component is distinct from the AD7874 or AD7876, which lack the integrated FIFO and DSP-specific interface logic found in the AD7878 architecture.

Replacement Considerations

Public confirmed substitutes include AD7878JN, AD7878KN, AD7878LN, AD7878AQ, AD7878SQ, AD7878JP, AD7878KP, and AD7878LP. Note that variations exist in temperature range, package type, and data access time (41 ns vs 57 ns) across these alternatives.