Analog Devices Inc. 1B21AN

Overview

1B21AN from Analog Devices is an isolated, loop-powered voltage-to-current converter designed for industrial process control signal conditioning. It accepts 0 V to 10 V input, delivers programmable 4 mA to 20 mA or 0 mA to 20 mA output, provides 1500 V_rms galvanic isolation, and operates across −25°C to +85°C with ±0.02% nonlinearity and ±50 ppm/°C gain tempco.

For engineers reviewing the 1B21AN datasheet, 1B21AN pinout, 1B21AN application, or 1B21AN equivalent, key selection considerations include its transformer-isolated architecture, resistor-programmable input gain/offset, loop-side compliance up to 27 V, low-drift reference (±15 ppm/°C), and DIP-8 package compatibility with AC1060 socket mounting.

Technical Context

The 1B21AN implements transformer-based signal and power isolation: a 25 kHz oscillator drives T2 for output-side power generation and T1 for amplitude-modulated signal transfer. Its input stage is an inverting amplifier with user-configurable RI, RF, and RO resistors to set gain, span, and 4 mA offset-enabling precise mapping of 0 V–10 V inputs to 0–20 mA or 4–20 mA outputs.

Demodulation and filtering on the output side reconstruct a control voltage for the current source, which drives the external loop load. The internal +6.225 V reference (±1.0% error, ±15 ppm/°C) enables accurate 4 mA offset generation without external components, while CMR ≥90 dB at 60 Hz suppresses common-mode interference in noisy industrial environments.

Key Specifications

Pinout & Package

1B21AN uses an 8-lead nonstandard DIP package (1B21-N-08), measuring 0.7″ × 2.1″ × 0.35″ (17.8 × 53.3 × 8.9 mm), compatible with AC1060 socket mounting. Pin numbering follows bottom-view orientation per Figure 2 of Rev. C datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar isolated voltage-to-current conversion applications.

Compared with AD421BN and ISO124U, the 1B21AN uniquely combines transformer-isolated signal conversion, programmable analog scaling via resistors, and integrated loop-powered current sourcing - delivering a self-contained solution for legacy analog systems where simplicity, reliability, and minimal external components are prioritized over digital features or bandwidth.

Availability

1B21AN is available at Aetrix Electronics and suitable for industrial process control, analog transmitter interfacing, and multichannel data acquisition systems requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for 1B21AN 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 semiconductor company specializing in high-performance analog, mixed-signal, and digital signal processing technologies for industrial, automotive, communications, and healthcare applications.

The 1B21AN belongs to Analog Devices' legacy industrial signal conditioning product line, engineered specifically for robust, transformer-isolated analog I/O in harsh electromagnetic environments - emphasizing galvanic separation, low drift, and field-deployable reliability over decades.

FAQ

What is the operating temperature range for the 1B21AN?

The 1B21AN is fully specified for rated performance from −25°C to +85°C and operates across the extended industrial range of −40°C to +85°C. Its ±50 ppm/°C gain tempco and ±300 nA/°C offset tempco ensure stable calibration over this full range without active compensation, making it suitable for outdoor or unconditioned cabinet deployments where ambient temperatures fluctuate widely.

How does the 1B21AN achieve galvanic isolation without optocouplers?

The 1B21AN uses transformer-based isolation: a 25 kHz oscillator drives transformer T2 for output-side power generation and transformer T1 for amplitude-modulated signal transfer. This dual-transformer architecture provides 1500 V_rms continuous isolation between input and output sides, eliminating LED aging and CTR drift issues associated with optocouplers while maintaining high CMR (≥90 dB at 60 Hz).

Can the 1B21AN be configured for both 0–20 mA and 4–20 mA output ranges?

Yes, the 1B21AN supports both output ranges via external resistor configuration. For 0–20 mA, only RI and RF are used; for 4–20 mA, RO is added to inject offset current from the internal +6.225 V reference. Table 2 in the datasheet provides exact resistor values (e.g., RI = 50 kΩ, RF = 20 kΩ, RO = 124.3 kΩ for 0–10 V input → 4–20 mA output), enabling precise, repeatable setup without trimming.

What is the maximum load resistance supported by the 1B21AN in a 4–20 mA loop?

The 1B21AN supports up to 1.35 kΩ load resistance when powered by a 30 V loop supply, based on its 27 V minimum load compliance voltage. This allows operation over long cable runs (e.g., >1 km of 24 AWG twisted pair) while maintaining full 4–20 mA regulation, provided the loop supply voltage remains ≥30 V and total series resistance (load + wiring) stays within the 1.35 kΩ limit.

Does the 1B21AN require external power supplies on both input and loop sides?

Yes - the 1B21AN requires ±15 V analog supplies on the input side (pins 20 and 22) to power its internal circuitry and oscillator, and a separate +15 V to +30 V loop supply connected in series with the load on the output side (between OUT HIGH and the load). It is not loop-powered on the input side; the "loop-powered" designation refers only to the output current loop being externally energized.