Analog Devices Inc. AD7878BQ

Overview

AD7878BQ from Analog Devices is a complete 12-bit, 100 kHz sampling analog-to-digital converter with integrated track/hold amplifier, on-chip 3 V Zener reference, and 8-word FIFO for DSP interfacing. It delivers 72 dB SNR at 10 kHz input, 41 ns data access time, and operates over –25°C to +85°C in a 28-pin cerdip (Q-28) package. It is used in high-speed speech recognition systems where low-latency digitization of ±3 V bipolar signals is required.

For engineers reviewing the AD7878BQ datasheet, AD7878BQ pinout, AD7878BQ application, or AD7878BQ equivalent, this page provides verified technical context, real-world timing behavior, FIFO control semantics, dynamic performance boundaries, and precise interface compatibility with ADSP-2100 and TMS320-series DSPs - all confirmed from Analog Devices' official REV. A datasheet.

Technical Context

The AD7878BQ implements a successive approximation ADC core synchronized to an external 8 MHz CLK IN, with internal clock division yielding 500 ns bit trial cycles. Its 8-word FIFO uses a ripple-down architecture where reads access Location 0 while new conversions enter at the top, and the address pointer increments post-conversion.

Conversion is initiated asynchronously via CONVST; BUSY goes low on the next CLK IN rising edge and remains low until hold mode is established. The status/control register (accessible via ADD0 = high) enables programmable ALFL threshold (1–8 words), FIFO overrun detection (FOVR), output disable during BUSY (DISO), and sample out-of-range flagging (SOOR).

Key Specifications

Pinout & Package

AD7878BQ is housed in a 28-pin cerdip (Q-28) hermetic package, rated for –25°C to +85°C operation. Pin layout follows standard dual-in-line footprint with gull-wing leads, compatible with automated SMT assembly and MIL-STD-883B screening options.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7878LN, AD7878BQ offers extended temperature operation and hermetic reliability for field-deployed DSP systems; compared with AD7865BS, it trades resolution for integrated FIFO and lower software overhead - making it optimal for single-channel, latency-critical, interrupt-driven DSP applications.

Availability

AD7878BQ is available at Aetrix Electronics and suitable for digital signal processing, speech recognition systems, and spectrum analysis equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for AD7878BQ 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 AD7878BQ belongs to Analog Devices' LC2MOS precision ADC product line, designed specifically for seamless integration with real-time DSP processors in bandwidth-constrained, low-latency signal acquisition systems.

FAQ

What is the guaranteed SNR performance of the AD7878BQ across its operating temperature range?

The AD7878BQ guarantees a minimum 72 dB signal-to-noise ratio at 10 kHz input frequency and 25°C, and 71 dB minimum from –25°C to +85°C per Analog Devices REV. A datasheet. This specification is 100% production tested and applies to full-scale ±3 V sine wave inputs sampled at 100 kHz - critical for maintaining voice clarity in speech synthesis applications where the AD7878BQ is deployed.

How does the AD7878BQ's FIFO interact with the status/control register during read operations?

The AD7878BQ uses ADD0 to multiplex the 12-bit data bus: when ADD0 is low, reads access FIFO Location 0; when ADD0 is high, reads return the status/control register contents. Reading the status register (e.g., to check FEMP or SOOR) does not alter FIFO contents or pointer position - allowing non-destructive status monitoring before each data word retrieval. This behavior is explicitly defined in the AD7878BQ datasheet Section "STATUS/CONTROL REGISTER".

Can the AD7878BQ operate with asynchronous CONVST pulses while the DSP is performing memory reads?

Yes - the AD7878BQ supports asynchronous CONVST initiation independent of CLK IN, CS, DMWR, or DMRD. When CONVST asserts, BUSY goes low on the next CLK IN rising edge. If DB5 (DISO) is set to 0, the data bus remains disabled during BUSY, preventing corruption. The gated BUSY/CS signal can then stretch the DSP instruction cycle via READY/DTACK, enabling safe concurrent operation - a key feature confirmed in the AD7878BQ "Extended Read/Write Operation" section.

What is the maximum allowable capacitive load on the AD7878BQ's REF OUT pin?

The AD7878BQ REF OUT pin supports a maximum capacitive load of 50 pF without external compensation. For loads exceeding 50 pF, a series resistor (value determined by load impedance and stability requirements) must be added between REF OUT and the load capacitor, as specified in the AD7878BQ datasheet "Internal Reference" section. Exceeding this limit risks reference regulation error and degraded SNR performance in precision ADC applications.

Does the AD7878BQ support simultaneous read and write operations to its FIFO and status register?

No - the AD7878BQ does not support true simultaneous read/write. Its bus protocol is strictly sequential: ADD0 selects the target (FIFO or status register), and DMRD/DMWR strobes determine direction. However, the status register allows atomic control of FIFO behavior (e.g., writing to DB5 to disable outputs during BUSY), and reading status bits like FEMP or SOOR provides real-time FIFO state without affecting data flow - a capability fully documented for the AD7878BQ in the "STATUS/CONTROL REGISTER FUNCTION DESCRIPTION" table.