Texas Instruments UC3901Q

Overview

UC3901Q 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 delivers ±2.8 V driver output swing to drive RF transformers or capacitive couplers.

For engineers reviewing the UC3901Q datasheet, UC3901Q pinout, UC3901Q application, or UC3901Q equivalent, key selection considerations include its 0°C to +70°C operating range, PLCC-20 package with 20-pin leadframe, status monitor output active-low within ±150 mV of reference, and compatibility with external clock synchronization at Pin 2.

Technical Context

The UC3901Q uses an internal amplitude-modulation architecture where the error amplifier's compensation terminal (Pin 12) feeds a modulator stage that drives two emitter-follower outputs (DRIVERA and DRIVERB) with fixed 12 dB gain and 50% duty cycle when using the internal oscillator. Its carrier frequency is programmable via RT/CT pins and supports up to 5 MHz with external clock input.

It integrates UVLO activation at 3.9–4.5 V on VIN, disables all outputs until supply stabilization, and provides loop status monitoring via an active-low STATUS output triggered when error voltage deviates ≤±150 mV from the 1.5 V reference - enabling real-time fault detection in isolated SMPS feedback paths.

Key Specifications

Pinout & Package

UC3901Q is housed in a 20-lead PLCC (FN package) with gull-wing leads, moisture sensitivity level 2 (260°C peak reflow), RoHS-compliant tin-lead finish, and body dimensions of 9.0 mm × 9.0 mm × 3.1 mm.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC2901Q and UC3901D, the UC3901Q uniquely balances commercial-temperature operation, full feature set (including STATUS), and PLCC-20 mechanical robustness - making it optimal for cost-sensitive, volume production of regulated AC-DC and telecom power supplies.

Availability

UC3901Q is available at Aetrix Electronics and suitable for AC-DC adapters, industrial SMPS, medical power supplies, and programmable lab PSUs requiring stable component supply, consistent parametric performance, and long-term sourcing continuity.

Supply support for UC3901Q 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 UC3901Q belongs to TI's legacy isolated feedback generator product line, engineered specifically to replace optocouplers in regulated switch-mode power supplies by enabling transformer- or capacitor-coupled error signal transmission with improved accuracy and reliability.

FAQ

What is the operating temperature range of the UC3901Q?

The UC3901Q is specified for operation from 0°C to +70°C - the commercial temperature grade within the UC1901/UC2901/UC3901 family. This range is validated per TI's datasheet Electrical Characteristics table for UC3901, with parameters such as reference voltage (1.455–1.545 V), oscillator accuracy (120–180 kHz), and error amplifier offset (≤8 mV) guaranteed across this interval. The UC3901QTRG3 tape-and-reel variant maintains this rating.

Does the UC3901Q support external clock synchronization?

Yes, the UC3901Q 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 an external TTL/CMOS clock signal at Pin 2 to control carrier frequency and duty cycle. This capability allows alignment of the modulation frequency with the SMPS switching node - reducing EMI and improving system-level noise immunity in the UC3901Q-based design.

What is the function of the STATUS output on the UC3901Q?

The STATUS output (Pin 13) is an active-low open-collector indicator that asserts low when the error amplifier inputs are within ±150 mV of the internal 1.5 V reference - signaling loop convergence. In the UC3901Q, this output remains high-impedance until VIN exceeds the UVLO threshold (3.9–4.5 V), then transitions low only during valid regulation. It is commonly used for fault flagging, enable sequencing, or microcontroller interrupt generation in UC3901Q-powered systems.

Can the UC3901Q drive an optocoupler directly?

Yes, the UC3901Q can drive an optocoupler directly in DC mode. Its DRIVERA and DRIVERB outputs function as emitter followers capable of sourcing ≥15 mA - sufficient to forward-bias standard optocoupler LEDs. The UC3901Q's 4.5–40 V supply range, 1% reference, and high-gain error amplifier provide advantages even when AC transformer coupling is not used, making it a flexible solution for both RF-modulated and DC-driven isolation interfaces in UC3901Q implementations.

What package type is used for the UC3901Q?

The UC3901Q uses a 20-lead PLCC (Plastic Leaded Chip Carrier) package with FN drawing code, gull-wing leads, and RoHS-compliant tin-lead finish. Its dimensions are 9.0 mm × 9.0 mm × 3.1 mm, and it carries JEDEC MSL Level-2 moisture sensitivity (260°C peak reflow). This package is distinct from SOIC-14 (UC3901D) and SOIC-16 (UC3901DW) variants, and shares pin compatibility only with other PLCC-20 members of the UCx901 family such as UC2901Q.