Texas Instruments UC3842ADG4

Overview

UC3842ADG4 from Texas Instruments is a current-mode PWM controller IC designed for off-line and DC-DC switch-mode power supplies. It features 500 kHz maximum switching frequency, <0.5 mA start-up current, 8.3 mA trimmed oscillator discharge current, undervoltage lockout with hysteresis (14.5 V turn-on / 8.5 V turn-off), and a 1 A totem-pole output stage driving MOSFET gates directly in flyback and forward converters.

For engineers reviewing the UC3842ADG4 datasheet, UC3842ADG4 pinout, UC3842ADG4 application, or UC3842ADG4 equivalent, key selection criteria include its 8-pin SOIC (D) package, peak-current-mode control architecture, 5 V ±1% internal reference, pulse-by-pulse current limiting, and compatibility with universal-input AC/DC adapter designs requiring stable duty-cycle programming and low-noise error amplifier performance.

Technical Context

The UC3842ADG4 implements fixed-frequency peak-current-mode control using an internal oscillator with programmable RT/CT timing network, a high-gain (80 dB) error amplifier with 1 MHz unity-gain bandwidth, and a current-sense comparator clamping peak ISENSE at 1 V. Its UVLO circuit ensures controlled startup with 1.5 V hysteresis and enables sinking ≥10 mA during lockout.

It operates in continuous or discontinuous conduction mode, supports automatic feedforward compensation via the FB pin, and delivers up to 96% maximum duty cycle. The device integrates a short-circuit protected 5 V reference (±1% over temperature), 1-A gate driver with 25–150 ns rise/fall times, and double-pulse suppression logic to prevent false triggering.

Key Specifications

Pinout & Package

UC3842ADG4 is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, optimized for surface-mount assembly and thermal dissipation in compact power modules.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar current-mode PWM controller applications.

Compared with UC3842BDG4, UC3842ADG4 trades minor reference and oscillator tolerance for lower cost and broader availability; versus TL494CN, it delivers integrated current-mode control and gate drive but lacks dual-output flexibility-making UC3842ADG4 optimal for cost-sensitive, single-switch flyback or forward converters.

Availability

UC3842ADG4 is available at Aetrix Electronics and suitable for AC/DC adapters, flyback PSUs, and industrial DC-DC converters requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for UC3842ADG4 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 leader delivering analog, embedded processing, and power management solutions with emphasis on reliability, efficiency, and system-level integration.

The UC3842ADG4 belongs to TI's UCx84xA family of current-mode PWM controllers, engineered specifically for cost-effective, high-efficiency off-line and isolated DC-DC power conversion in consumer, industrial, and telecom applications.

FAQ

What is the maximum operating frequency of the UC3842ADG4?

The UC3842ADG4 supports oscillator frequencies up to 500 kHz, enabling compact magnetic design and reduced filter component size. This maximum is achievable with appropriate RT/CT values-TI recommends RT between 5 kΩ and 100 kΩ and CT between 470 pF and 4.7 nF. Frequency stability is maintained across temperature due to the trimmed 8.3 mA oscillator discharge current. The UC3842ADG4 datasheet confirms this rating under recommended operating conditions.

Does the UC3842ADG4 require an external gate driver?

No, the UC3842ADG4 does not require an external gate driver. Its integrated totem-pole output stage sources and sinks up to 1 A of peak current, sufficient to directly drive the gate of medium-power N-channel MOSFETs used in ≤100 W flyback and forward converters. The OUTPUT pin's 25–150 ns rise/fall times support efficient switching at up to 500 kHz. External series gate resistors are still recommended for EMI control and ringing suppression in the UC3842ADG4 layout.

What is the purpose of the VREF pin on the UC3842ADG4?

On the UC3842ADG4, the VREF pin delivers a precision 5 V ±1% output used for multiple functions: biasing the RT/CT timing network, powering opto-isolator LEDs in isolated feedback paths, and serving as a stable reference for external voltage dividers. It is short-circuit protected at ~100 mA and must supply no more than 10 mA under normal operation. A 1 µF high-frequency bypass capacitor is required per the UC3842ADG4 datasheet to maintain stability.

How does the UC3842ADG4 implement current limiting?

The UC3842ADG4 implements pulse-by-pulse current limiting via its ISENSE pin, which feeds a comparator that clamps the peak sensed voltage at 1 V. When the current-sense resistor voltage reaches this threshold, the PWM latch resets immediately, terminating the current pulse. This cycle-resolved protection is inherent to peak-current-mode control and requires no external latching circuitry. The UC3842ADG4's 1 V clamp is internally trimmed and stable over temperature, ensuring repeatable current limits across operating conditions.

What is the UVLO behavior of the UC3842ADG4 during power-up?

During power-up, the UC3842ADG4 remains in undervoltage lockout (UVLO) until VCC rises to 14.5 V (typical turn-on threshold). While in UVLO, the IC draws <0.5 mA, the OUTPUT pin stays low, and the internal reference is inactive. Once VCC exceeds the threshold, the device activates fully: VREF rises to 5 V, the oscillator starts, and normal PWM operation begins. If VCC drops below 8.5 V (turn-off threshold), the UC3842ADG4 re-enters UVLO, halting switching and pulling OUTPUT low to prevent parasitic MOSFET turn-on.