AD421BN

Overview

The AD421BN is a loop-powered, 16-bit digital-to-analog converter (DAC) designed for industrial control smart transmitters. It generates a 4 mA to 20 mA current output with 16-bit monotonicity and ±0.01% integral nonlinearity. The device integrates a selectable voltage regulator providing +5 V, +3.3 V, or +3 V outputs, alongside precision +2.5 V and +1.25 V reference sources. It operates on a single supply of 2.95 V to 5.05 V, features a high-speed 3-wire serial interface supporting up to 10 Mbps, and includes programmable alarm current capabilities. The component is housed in a 16-lead plastic DIP package and functions within an industrial temperature range of –40 °C to +85 °C.

Feature Summary

• 16-bit sigma-delta DAC architecture ensuring guaranteed monotonicity and ±0.01% INL.
• Integrated selectable voltage regulator (+5 V, +3.3 V, or +3 V) and precision references (+2.5 V, +1.25 V).
• HART® protocol compatible with standard FSK communication circuitry.
• Programmable alarm current capability allowing output outside the standard 4–20 mA range.

Applications

• Smart industrial control transmitters requiring loop-powered operation.
• High-resolution extension for existing 4 mA to 20 mA transmitter systems.
• Applications utilizing HART® communication protocols for data transmission.

Procurement Notes

Verify that the ordering suffix 'BN' corresponds to the Plastic DIP package variant as specified in the Analog Devices Ordering Guide. Confirm that the required operating temperature range aligns with the B version specification of –40 °C to +85 °C. Ensure external components, such as the depletion mode FET pass transistor, are selected to meet breakdown voltage requirements for the specific loop voltage application.

Selection Notes

Select the AD421BN when a through-hole DIP package is required for the system design. The part supports both normal 4–20 mA operation and alarm current modes via the serial interface. Designers must account for the external N-channel depletion mode FET required for the voltage regulator loop. Ensure the microcontroller interface matches the 3-wire serial timing requirements, specifically the clock period and latch delay specifications.

Part Context

The AD421 series serves as a complete solution for generating 4 mA to 20 mA signals in smart transmitters. The AD421BN specifically denotes the B grade version packaged in a 16-lead Plastic DIP (N-16). This contrasts with the SOIC variants, such as the AD421BR, which utilize surface-mount technology. The B version is rated for the industrial temperature range.

Replacement Considerations

The AD421BR is the equivalent surface-mount alternative in the same family. For higher performance requirements, the AD5421 offers enhanced specifications but differs in pinout and feature set. Direct pin-compatible replacements are not explicitly listed in the provided documentation.