Analog Devices Inc. AD7878AQ

Overview

AD7878AQ 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 70 dB SNR at 10 kHz input, 41 ns data access time (L-grade variant), and operates over –25°C to +85°C. It serves as a high-speed digitizer in real-time signal acquisition systems interfacing directly with ADSP-2100 or TMS320xx processors.

For engineers reviewing the AD7878AQ datasheet, AD7878AQ pinout, AD7878AQ application, or AD7878AQ equivalent, key selection considerations include its bipolar ±3 V analog input range, FIFO programmable almost-full threshold, BUSY-synchronized read/write control, and LC2MOS process–enabled low-power (60 mW typ) operation in demanding DSP front-end designs.

Technical Context

The AD7878AQ implements a successive approximation register (SAR) ADC core with asynchronous CONVST triggering and internal clock division (÷4) for bit trials. Its 8-word FIFO operates with address pointer increment-on-conversion and ripple-down read behavior synchronized to CLK IN.

Control logic includes a 12-bit status/control register accessible via ADD0-high reads/writes, supporting ALFL flag programming (DB10–DB8), FIFO overrun/out-of-range monitoring (DB6, DB5), and output disable during BUSY (DB5 = 0). All timing parameters-including t9 = 57 ns data access-are fully specified across –25°C to +85°C.

Key Specifications

Pinout & Package

AD7878AQ is housed in a 28-pin cerdip (Q-28) hermetic package, rated for –25°C to +85°C operation and compatible with standard DIP socket footprints.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7878LN, AD7878AQ trades 16 ns slower access time for extended –25°C to +85°C operation and improved reliability in industrial environments; versus AD7865BS, it delivers lower system cost and simpler firmware through integrated FIFO, reference, and DSP-native control signals - at the expense of channel count and resolution.

Availability

AD7878AQ is available at Aetrix Electronics and suitable for digital signal processing front-ends, speech recognition hardware, and spectrum analyzer subsystems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for AD7878AQ 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, headquartered in Norwood, MA.

The AD7878AQ belongs to Analog Devices' LC2MOS precision ADC product line, engineered specifically for real-time DSP interfacing with integrated FIFO, reference, and asynchronous sampling - targeting applications where low software overhead and guaranteed ac performance are critical.

FAQ

What is the operating temperature range of the AD7878AQ?

The AD7878AQ is rated for operation from –25°C to +85°C. This extended industrial temperature range distinguishes it from commercial-grade variants like AD7878JN (0°C to +70°C) and makes it suitable for deployment in harsher environments such as factory automation controllers or outdoor communications equipment. The full set of dynamic and dc specifications - including 70 dB SNR and ±6 LSB full-scale error - is guaranteed across this entire range.

Does the AD7878AQ require an external reference voltage?

No, the AD7878AQ includes an on-chip 3 V Zener reference provided at the REF OUT pin. This internal reference is specified to ±10 mV at 25°C and ±15 mV over the full –25°C to +85°C range. It can source up to 500 µA, but for capacitive loads exceeding 50 pF, a series resistor must be added per the datasheet's Internal Reference section to maintain stability. No external reference IC is needed for standard operation.

How does the FIFO in the AD7878AQ function during continuous sampling?

The AD7878AQ contains an 8-word first-in, first-out (FIFO) memory that automatically stores conversion results as they complete. Each new conversion increments the internal address pointer and writes to the top of the FIFO. Reads access Location 0 and cause all remaining words to shift down by one position. The ALFL flag - programmable via DB10–DB8 in the status/control register - asserts when the word count reaches a user-defined threshold (1–8), enabling interrupt-driven buffer management without polling overhead in real-time DSP firmware.

Can the AD7878AQ interface directly with the ADSP-2100 processor?

Yes, the AD7878AQ is explicitly designed for seamless interfacing with the ADSP-2100. Its control signals map directly: DMWR corresponds to ADSP-2100's DMWR, DMRD to DMRD, and BUSY can be connected to the processor's READY input to generate WAIT states. The 57 ns data access time meets ADSP-2100 timing requirements, and the 8-word FIFO reduces interrupt frequency - collectively enabling efficient, low-overhead data streaming without external glue logic.

What is the purpose of the DISO bit (DB5) in the AD7878AQ status/control register?

The DISO bit (DB5) in the AD7878AQ status/control register controls whether the three-state output drivers are disabled during BUSY low. When DB5 = 0, data bus activity is blocked while the track/hold transitions from track to hold mode - preventing internal transients from corrupting the held analog value. When DB5 = 1, outputs remain enabled during BUSY low, allowing read/write operations to proceed without WAIT-state extension. This bit enables flexible timing coordination based on host processor capabilities.