Texas Instruments UC3901DW

Overview

UC3901DW 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 (1–5 MHz carrier) using a 1% internal reference, error amplifier with 60 dB CMRR, and dual emitter-follower driver outputs capable of ±2.8 V swing and 15 mA source current. It operates from 4.5 V to 40 V and supports external clock synchronization.

For engineers reviewing the UC3901DW datasheet, UC3901DW pinout, UC3901DW application, or UC3901DW equivalent, key selection considerations include its SOIC-16 DW package, 0°C to +70°C temperature grade, transformer-coupled feedback architecture, UVLO threshold at 3.9 V, and status monitor output active-low within ±150 mV of reference.

Technical Context

The UC3901DW integrates a programmable oscillator (130–180 kHz typical over temperature), error amplifier with 1 MHz gain-bandwidth product and 0.3 V/µs slew rate, and modulator drivers with fixed 12 dB gain from compensation pin to output. Its STATUS output asserts low when error voltage deviates ≤±150 mV from the 1.5 V reference, enabling loop health monitoring.

Driver outputs (DRIVERA and DRIVERB) are emitter followers with 15 mA sourcing capability and 700 µA internal sink limit-expandable via external pull-down resistors. The device enables only after VIN exceeds 4.5 V (UVLO), and features internal 1% reference accuracy with ±15 mV load regulation over 0–5 mA.

Key Specifications

Pinout & Package

UC3901DW is housed in a 16-pin SOIC Wide (DW) package per JEDEC MS-013AC, with 1.27 mm pitch and exposed pad not present. Thermal resistance θ_JA = 100°C/W (typical).

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC2901DW, UC3901DW trades extended temperature operation for lower cost and tighter production binning in commercial environments; compared with LM5018, UC3901DW delivers transformer-coupled feedback without optocoupler latency or CTR drift but requires external power stage design.

Availability

UC3901DW is available at Aetrix Electronics and suitable for industrial AC-DC adapters, telecom rectifiers, medical power supplies, and programmable lab PSUs requiring stable component supply, RoHS-compliant packaging, and long-term lifecycle support.

Supply support for UC3901DW 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 communications markets since 1930.

The UC3901DW belongs to TI's legacy isolated control IC product line, engineered specifically to replace optocouplers in regulated SMPS feedback paths using RF transformer coupling - targeting cost-sensitive, high-reliability power conversion applications.

FAQ

What is the function of Pin 1 (CR) on the UC3901DW?

Pin 1 (CR) on the UC3901DW connects to the timing capacitor that sets the internal oscillator frequency. When CR is tied to VIN, the internal oscillator is disabled and the device accepts an external clock signal on Pin 2 (CLK). This allows synchronization to the SMPS switching frequency, reducing EMI and avoiding beat frequencies. The UC3901DW oscillator operates from 120 kHz to 180 kHz over temperature with RT = 10 kΩ and CT = 820 pF.

Does the UC3901DW require external components to operate?

Yes, the UC3901DW requires external components for full operation: a timing capacitor on Pin 1 (CR), feedback resistors connecting Pins 5 (EA–) and 6 (EA+) to the secondary-side voltage divider, and an RF transformer or capacitor between Pins 9 (DRIVERB) and 10 (DRIVERA) and the secondary-side rectifier. A pull-up resistor on Pin 11 (STATUS) is also needed for active-low logic interfacing. The UC3901DW integrates the reference, error amplifier, oscillator, and drivers - eliminating need for discrete counterparts.

How does the STATUS output of the UC3901DW indicate loop health?

The STATUS output of the UC3901DW is an active-low open-collector pin that asserts low when the error amplifier input differential voltage is within ±150 mV of the 1.5 V internal reference - indicating the power supply output is regulated within approximately ±10% of target. It remains high during startup, overload, or open-loop faults. The UC3901DW STATUS pin can directly drive an LED or microcontroller GPIO with appropriate pull-up; leakage is <5 µA when high and saturation voltage is 0.45 V at 1.6 mA sink.

Can the UC3901DW be used with optical couplers?

Yes, the UC3901DW can drive optical couplers as a DC-coupled error amplifier: its DRIVERA and DRIVERB outputs provide ≥15 mA source current and can sink up to 700 µA (extendable with external resistors), making them compatible with standard optocoupler LED anodes. The UC3901DW's 1% reference, 4.5–40 V supply range, and high-gain error amplifier offer advantages even in DC-coupled configurations - though its primary design intent is RF transformer coupling for lower latency and drift-free isolation.

What is the thermal performance of the UC3901DW in SOIC-16 DW package?

The UC3901DW in SOIC-16 DW package has a typical junction-to-ambient thermal resistance (θ_JA) of 100°C/W on standard 2-layer PCBs with 1 in² copper pour. Maximum power dissipation is 1000 mW at TA = 25°C and 2000 mW at TC = 25°C. The device operates from 0°C to +70°C ambient, with maximum junction temperature limited to +150°C. Derating is required above 25°C ambient per the thermal curve in the UC3901DW datasheet - confirming safe operation under full-load conditions in typical power supply layouts.