Analog Devices Inc. AD7878KP

Overview

AD7878KP 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 0°C to +70°C with ±3 V bipolar analog input range - deployed in high-speed modems and DSP servo control systems.

For engineers reviewing the AD7878KP datasheet, AD7878KP pinout, AD7878KP application, or AD7878KP equivalent, this page provides verified technical context, real-world timing behavior, FIFO-controlled throughput trade-offs, and direct interface compatibility with ADSP-2100 and TMS320xx processors.

Technical Context

The AD7878KP implements a successive approximation ADC core synchronized to an external 8 MHz TTL-compatible CLK IN, with internal clock division yielding 500 ns bit trial cycles. Its 8-word FIFO uses ripple-down architecture where reads access Location 0 while new conversions enter at the top, requiring synchronous clocking between microprocessor and CLK IN to avoid read/write conflicts.

Conversion initiation is fully asynchronous via CONVST, with BUSY signaling track-to-hold transition; ALFL status is programmable (1–8 words) via DB10–DB8 in the status/control register, and output drivers can be disabled during BUSY low by writing 0 to DB5 (DISO) to prevent bus transients from corrupting hold voltage.

Key Specifications

Pinout & Package

AD7878KP is housed in a 28-pin Plastic Leaded Chip Carrier (PLCC, package code P-28A), with gull-wing leads, JEDEC MS-026 compliant footprint, and 1.27 mm pitch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD7878KP, AD7879KP adds gain flexibility at the expense of cost and power, while ADS8320U trades parallel DSP interface and FIFO for higher resolution and serial simplicity - neither is pin- or code-compatible, making AD7878KP the sole drop-in solution for legacy ADSP-2100 systems requiring 12-bit, 100 kHz, FIFO-buffered acquisition.

Availability

AD7878KP is available at Aetrix Electronics and suitable for digital signal processing, speech recognition, and DSP servo control applications requiring stable component supply across industrial temperature ranges and long-lifecycle programs.

Supply support for AD7878KP 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, founded in 1965 and headquartered in Wilmington, MA.

The AD7878KP belongs to Analog Devices' LC2MOS precision ADC product line, engineered specifically for seamless integration with real-time DSP processors through hardware-accelerated FIFO buffering and asynchronous sampling control.

FAQ

What is the maximum sampling rate supported by the AD7878KP?

The AD7878KP supports a maximum sampling rate of 100 kHz, validated across its full 0°C to +70°C operating range. This rate is achievable using an 8 MHz CLK IN and accounts for worst-case conversion time of 7.125 µs with no external read/write operations. At this rate, the device fully resolves input signals up to 50 kHz per the Nyquist-Shannon sampling theorem, and maintains 72 dB SNR performance at 10 kHz input frequency as specified in the AD7878KP datasheet.

Does the AD7878KP require an external reference voltage?

No, the AD7878KP does not require an external reference voltage. It integrates a precision 3.0 V Zener reference (REF OUT) with ±10 mV accuracy at 25°C and ±15 mV over temperature. This on-chip reference drives the ADC core directly and is rated for 500 µA load current. External loading beyond 50 pF requires a series resistor per the AD7878KP datasheet, but no external reference IC or trimming components are needed for standard operation.

How does the FIFO in the AD7878KP reduce software overhead in DSP systems?

The AD7878KP's 8-word FIFO allows up to eight consecutive conversions to be stored before the DSP must service the device. This eliminates the need for per-sample interrupt handling, reducing CPU interrupt load by up to 8×. Reads access Location 0 in first-in-first-out order, and the FIFO word count (DB2–DB0) and ALFL flag provide real-time status - enabling efficient burst-mode data transfers aligned with DSP DMA engines or block-processing algorithms.

Can the AD7878KP interface directly with the ADSP-2100 processor?

Yes, the AD7878KP interfaces directly with the ADSP-2100 processor without glue logic. Its DMRD, DMWR, and BUSY signals map natively to ADSP-2100's DMRD, DMWR, and READY pins. The 41 ns data access time meets ADSP-2100's timing requirements, and the asynchronous CONVST input allows precise sampling synchronization. The AD7878KP datasheet explicitly lists ADSP-2100 as a supported target, confirming full electrical and functional compatibility.

What is the purpose of the DISO bit (DB5) in the AD7878KP status/control register?

The DISO bit (DB5) in the AD7878KP status/control register controls whether the data bus outputs (DB11–DB0) are enabled during BUSY low. Writing 0 to DB5 disables outputs while BUSY is active, preventing data bus switching transients from disturbing the track/hold amplifier's held voltage - a critical feature for jitter-sensitive applications. Writing 1 allows outputs to remain active during BUSY low, supporting non-WAIT-state processors but requiring careful timing validation per the AD7878KP timing diagrams.