Texas Instruments UC3901N

Overview

UC3901N from Texas Instruments is an isolated feedback generator IC designed for closed-loop regulation across voltage isolation boundaries in switch-mode power supplies. It implements amplitude modulation using an internal 130–180 kHz oscillator (typ. 150 kHz), features a 1.5 V ±1.5% reference, integrated error amplifier with 60 dB CMRR and 100 dB PSRR, and provides DRIVERA/DRIVERB emitter-follower outputs for transformer-coupled feedback in AC-DC adapters and industrial SMPS.

For engineers reviewing the UC3901N datasheet, UC3901N pinout, UC3901N application, or UC3901N equivalent, this device serves as a low-cost, transformer-based alternative to optocouplers-offering supply range of 4.5–40 V, UVLO at 4.5 V, status monitoring with ±150 mV input window, and compatibility with external clock synchronization up to 5 MHz.

Technical Context

The UC3901N uses an internal amplitude-modulation architecture where the error amplifier output modulates a high-frequency carrier (130–180 kHz) generated by a programmable RC oscillator. The modulated signal drives two complementary emitter-follower outputs (DRIVERA and DRIVERB) capable of sourcing ≥15 mA and sinking ≥700 µA each, enabling direct drive of small RF transformers or capacitive isolation networks.

Its error amplifier includes internal compensation (unity-gain stable), 1 MHz gain-bandwidth product, 0.3 V/µs slew rate, and operates with common-mode input range from –0.5 V to +35 V. A dedicated STATUS output asserts active-low when the error amplifier's differential input falls within ±150 mV of the 1.5 V reference-enabling loop health monitoring without external circuitry.

Key Specifications

Pinout & Package

UC3901N is housed in a 14-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width and through-hole mounting. Thermal resistance θ_JA is 70°C/W; maximum power dissipation at T_A = 25°C is 1000 mW.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar isolated feedback generator applications.

Compared with UC2901N, UC3901N trades extended temperature support for lower cost and qualification scope-ideal for commercial power adapters. Versus LM5018, UC3901N delivers dedicated, high-fidelity isolated feedback without compromising controller flexibility or requiring optocoupler replacement.

Availability

UC3901N is available at Aetrix Electronics and suitable for AC-DC adapters, industrial SMPS, programmable power supplies, and medical isolated DC-DC modules requiring stable component supply, RoHS-compliant green packaging, and long-term production continuity.

Supply support for UC3901N 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

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, delivering analog, embedded processing, and connectivity solutions for industrial, automotive, and consumer markets since 1930.

The UC3901N belongs to TI's legacy power management interface IC family, specifically engineered to replace optocouplers in isolated feedback paths of switch-mode power supplies-prioritizing reliability, simplicity, and transformer-based isolation.

FAQ

What is the operating temperature range of the UC3901N?

The UC3901N is rated for 0°C to +70°C ambient operation, making it suitable for commercial-grade power supplies such as consumer AC-DC adapters and office equipment SMPS. This contrasts with the UC2901N (–40°C to +85°C) and UC1901J (–55°C to +125°C), which target industrial and military applications. The UC3901N's specifications-including reference voltage accuracy, oscillator frequency, and error amplifier performance-are guaranteed across this full range.

Can the UC3901N be synchronized to an external clock?

Yes, the UC3901N supports external clock synchronization via Pin 2 (CLK). When Pin 1 (CR) is tied to VIN, the internal oscillator is disabled and the device accepts a TTL/CMOS-compatible clock signal up to 5 MHz on Pin 2. This allows precise alignment of the carrier frequency with the main SMPS switching frequency-reducing beat interference and improving EMI performance. The UC3901N maintains full modulator functionality and driver output behavior under external clock mode.

How does the STATUS output function in the UC3901N?

The STATUS output of the UC3901N is an active-low, open-collector indicator that asserts when the error amplifier's differential input (EA+ minus EA–) falls within ±150 mV of the internal 1.5 V reference. This corresponds to the regulated condition-i.e., when output voltage is within ~1% of target. The output can directly interface with microcontroller interrupt pins or latch circuits. It remains high-impedance until supply reaches UVLO threshold (~4.5 V), ensuring clean startup behavior.

What package type is used for the UC3901N?

The UC3901N uses a 14-pin plastic dual in-line package (PDIP-N) with 0.3-inch body width and through-hole leads. It is RoHS-compliant and green (no Sb/Br flame retardants), with CU NIPDAU lead finish. This package is compatible with standard wave-solder and hand-solder processes, and its thermal resistance (θ_JA = 70°C/W) supports up to 1000 mW dissipation at 25°C ambient-sufficient for typical feedback generator duty cycles.

Does the UC3901N require external compensation components?

Yes, the UC3901N requires external compensation on Pin 7 (COMP), the error amplifier output terminal. A series RC network (typically 1–10 kΩ resistor + 1–10 nF capacitor) is connected between COMP and EA– to stabilize the control loop. The amplifier is internally compensated for unity-gain operation, but external components tailor phase margin and bandwidth to the specific power stage. TI's SLUS279A datasheet provides design examples for flyback and forward converters using the UC3901N.