Analog Devices Inc. AD7861AP

Overview

AD7861AP from Analog Devices is an 11-bit simultaneous-sampling analog-to-digital converter (ADC) with four-channel sample-and-hold, internal 2.5 V reference, ±2 LSB relative accuracy, and 3.2 µs per-channel conversion time at 12.5 MHz clock - designed for stator current acquisition in motor control systems and three-phase power measurement.

For engineers reviewing the AD7861AP datasheet, AD7861AP pinout, AD7861AP application, or AD7861AP equivalent, key selection considerations include simultaneous 4-channel sampling capability, channel sequencing via M0/M1 control, 12-bit parallel interface with D0 tied low, and P-44A ceramic LCC package compatibility with industrial temperature range (–40°C to +85°C).

Technical Context

The AD7861AP implements a successive approximation ADC architecture with a dedicated 4-channel SHA front-end that preserves phase relationships across VIN1–VIN3 and one auxiliary channel. Acquisition time is fixed at 1.6 µs (20 CLK cycles), independent of channel count, and conversion requires exactly 40 clock cycles per channel.

Channel selection is controlled by dual-mode logic: M1/M0 configure group size (2–4 channels), while S0/S1 select among AUX0–AUX3 for multiplexed auxiliary sampling. Data output uses twos-complement format, left-justified across D1–D11, with D0 hardwired low - requiring no external pull-down in interfacing.

Key Specifications

Pinout & Package

AD7861AP is housed in a 44-lead plastic leadless chip carrier (P-44A), hermetically sealed ceramic package with 0.050" pitch, rated for –40°C to +85°C operation. Pin 1 identifier located at top-left corner (top view, pins down). SGND, AGND, and DGND require star-point grounding near the device per layout guidelines.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar multichannel simultaneous-sampling ADC applications.

Compared with AD7861AP, AD7865-1ARSZ trades integrated reference and parallel interface for higher resolution and serial simplicity, while ADS8556IPMR delivers greater channel count and precision at the cost of larger footprint and higher power - making AD7861AP optimal for cost-constrained, DSP-coupled motor control where 11-bit phase coherence is sufficient.

Availability

AD7861AP is available at Aetrix Electronics and suitable for motor control systems, three-phase power monitoring, industrial data acquisition modules, DSP-based signal processing systems, and embedded energy metering applications requiring stable component supply across extended product lifecycles.

Supply support for AD7861AP 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, serving industrial, automotive, communications, and healthcare markets since 1965.

The AD7861AP belongs to Analog Devices' precision data acquisition ADC family, engineered specifically for real-time control and power electronics applications demanding simultaneous sampling, deterministic timing, and robust industrial-grade operation.

FAQ

What is the absolute maximum clock frequency supported by the AD7861AP?

The AD7861AP operates with an external system clock ranging from 6.25 MHz to 12.5 MHz. At 12.5 MHz, the minimum clock period is 80 ns, and conversion time per channel is precisely 40 clock cycles (3.2 µs). Exceeding 12.5 MHz violates the AC timing specifications and may cause BUSY assertion failure or data corruption in the AD7861AP.

How does the AD7861AP handle auxiliary channel selection during conversion?

The AD7861AP uses S0 and S1 pins to select one of AUX0–AUX3 prior to CONVST assertion; the selected channel is sampled simultaneously with VIN1–VIN3 (if enabled) and digitized in sequence. S0/S1 must be stable for at least two clock cycles before CONVST goes high - otherwise the AD7861AP may latch an indeterminate auxiliary channel value.

Is the internal 2.5 V reference of the AD7861AP usable without external components?

Yes - the AD7861AP's internal 2.5 V reference is fully functional when REFOUT is connected to REFIN. A 200 nF capacitor between REFIN and SGND is required per the datasheet to ensure stability and noise immunity; no additional regulators or buffers are needed for basic operation of the AD7861AP.

What is the function of the D0 pin on the AD7861AP, and why is it tied low?

D0 on the AD7861AP is permanently tied low to provide a fixed 12-bit bus interface while delivering only 11 bits of valid data (D1–D11). This design simplifies connection to 12-bit-wide data buses (e.g., ADSP-21xx) and ensures consistent left-justified twos-complement alignment - meaning the AD7861AP always outputs 11-bit resolution with D0 = 0, regardless of input voltage.

Can the AD7861AP perform conversions without an external clock source?

No - the AD7861AP requires an external clock input (CLK) between 6.25 MHz and 12.5 MHz to drive its internal timing, including SHA acquisition, conversion cycles, and BUSY pulse generation. There is no internal oscillator; omitting CLK or operating outside the specified range will halt all conversion activity and invalidate the AD7861AP's timing guarantees.