Texas Instruments UC3901DWTR

Overview

UC3901DWTR 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-modulated RF coupling via small transformers or capacitors, features a 1% internal reference, integrated error amplifier, and programmable oscillator up to 5 MHz, enabling compact, low-cost alternatives to optical couplers in AC-DC and DC-DC converters.

For engineers reviewing the UC3901DWTR datasheet, UC3901DWTR pinout, UC3901DWTR application, or UC3901DWTR equivalent, key selection considerations include its 0°C to +70°C operating range, SOIC-16 (DW) package, ±150 mV status input window, 12 dB modulator gain, and UVLO activation at 3.9 V - all critical for stable isolated feedback design in cost-sensitive industrial and consumer SMPS.

Technical Context

The UC3901DWTR uses an internal carrier oscillator (130–180 kHz typical over temperature) to generate a squarewave modulated by the error amplifier output, with fixed 50% duty cycle when using internal timing. Its error amplifier provides 40–60 dB open-loop gain and 60–80 dB CMRR, referenced to a 1.5 V ±1.5% bandgap source.

Driver outputs (DRIVERA/DRIVERB) operate as emitter followers capable of sourcing ≥15 mA and sinking ≥700 µA; STATUS output asserts active-low when error voltage falls within ±150 mV of the reference. The device enables only after VIN exceeds 3.9 V, ensuring reliable startup behavior in noisy supply environments.

Key Specifications

Pinout & Package

UC3901DWTR is housed in a 16-pin SOIC wide-body (DW) package with 1.27 mm pitch, RoHS-compliant Cu/NiPdAu lead finish, and JEDEC Level-2 moisture sensitivity rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC2901DTR, UC3901DWTR offers lower cost and smaller footprint for commercial-temperature applications but lacks extended thermal robustness; compared with LM5018MM/NOPB, UC3901DWTR provides dedicated, high-precision isolated feedback functionality without integrating power stage control logic.

Availability

UC3901DWTR is available at Aetrix Electronics and suitable for AC-DC adapters, isolated DC-DC converters, USB PD power supplies, and programmable lab PSUs requiring stable component supply, consistent parametric performance, and long-term manufacturability.

Supply support for UC3901DWTR 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 and embedded processing solutions for industrial, automotive, and consumer markets.

The UC3901DWTR belongs to TI's legacy isolated feedback IC product line, engineered specifically to replace optocouplers in cost-sensitive, medium-power SMPS designs where reliability, temperature stability, and minimal external components are critical.

FAQ

What is the primary function of the UC3901DWTR in a power supply design?

The UC3901DWTR serves as an isolated feedback generator that transmits regulation error signals across a transformer or capacitor barrier using amplitude modulation. It replaces optical couplers in switch-mode power supplies by generating a modulated RF carrier synchronized to the error voltage, enabling precise closed-loop control without LED aging or CTR degradation. The UC3901DWTR integrates a 1.5 V reference, error amplifier, oscillator, and dual driver outputs - all essential for implementing robust, low-drift isolated feedback in AC-DC and DC-DC converters.

Does the UC3901DWTR support external clock synchronization, and how is it implemented?

Yes, the UC3901DWTR supports external clock synchronization via Pin 2 (CLK). When Pin 1 (CR) is tied to VIN, the internal oscillator is disabled, and the modulator synchronizes to the external clock applied to Pin 2. This allows alignment of the carrier frequency with the main SMPS switching node, reducing beat frequencies and improving EMI performance. The UC3901DWTR accepts TTL/CMOS-level clock inputs and maintains 12 dB gain from COMP to DRIVER outputs regardless of clock source - a key feature confirmed in the device's Electrical Characteristics table and Application Information section.

What is the purpose of the STATUS output on the UC3901DWTR, and what triggers its assertion?

The STATUS output (Pin 11) is an active-low, open-collector indicator that asserts when the error amplifier's differential input voltage falls within ±150 mV of the 1.5 V reference - corresponding to ±10% regulation error. It monitors loop convergence in real time and can interface directly with supervisor ICs or latch circuits for overvoltage/undervoltage protection. The UC3901DWTR specifies this window as ±130 to ±170 mV over temperature, with typical value ±150 mV at 25°C, and requires a pull-up resistor for proper logic-level operation.

Can the UC3901DWTR be used with optical couplers, and if so, how?

Yes, the UC3901DWTR can drive optical couplers directly as a DC-coupled driver. Its DRIVERA and DRIVERB outputs function as emitter followers capable of sourcing ≥15 mA and sinking ≥700 µA - sufficient to bias standard optocoupler LEDs. In this configuration, the internal oscillator is disabled (Pin 1 → VIN), and the error amplifier output at Pin 5 (COMP) controls LED current linearly. The UC3901DWTR's 4.5–40 V supply range, 1% reference, and high-gain amplifier provide advantages even in DC-driven optocoupler applications, as noted in the device's Description section.

What are the key differences between UC3901DWTR and UC2901DTR beyond temperature rating?

Beyond the operating temperature range (UC3901DWTR: 0°C to +70°C vs. UC2901DTR: –40°C to +85°C), the UC3901DWTR and UC2901DTR share identical electrical specifications, pinout, and functional behavior - including reference voltage (1.47–1.53 V), oscillator accuracy (120–180 kHz), status window (±130–±170 mV), and driver capability. Both use SOIC packages (DW for 16-pin, D for 14-pin), but UC3901DWTR's DW package offers two additional NC pins for mechanical stability. No performance trade-offs exist between them outside thermal grade - making UC2901DTR a drop-in upgrade for extended environments while retaining full UC3901DWTR compatibility.