Texas Instruments UC3844AD8G4

Overview

UC3844AD8G4 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, 16 V/10 V undervoltage lockout (UVLO) thresholds, ≤50% max duty cycle, 8.3 mA trimmed oscillator discharge current, and 1 A totem-pole output drive - enabling compact, stable flyback and forward converter designs in industrial PSUs and battery-operated power modules.

For engineers reviewing the UC3844AD8G4 datasheet, UC3844AD8G4 pinout, UC3844AD8G4 application, or UC3844AD8G4 equivalent, key selection criteria include its fixed 50% max duty cycle limitation, SOIC-8 package compatibility, UVLO hysteresis for reliable start-up in unregulated inputs, and pulse-by-pulse current limiting for robust overcurrent protection in cost-sensitive AC/DC adapters.

Technical Context

The UC3844AD8G4 implements peak-current-mode control with an internal error amplifier (80 dB open-loop gain, 1 MHz unity-gain bandwidth), a precision 5 V bandgap reference (±1% over temperature), and a programmable oscillator using external RT/CT components. Its architecture integrates automatic feedforward compensation and double-pulse suppression to improve transient response and prevent false triggering during fault recovery.

It operates exclusively in current-mode control with a dedicated ISENSE input clamped at 1 V, COMP output driving the PWM comparator, and OUTPUT capable of sourcing/sinking 1 A. Unlike UC3842A/UC3843A variants, UC3844AD8G4 enforces ≤50% maximum duty cycle via internal logic - making it suitable for transformer-isolated topologies requiring duty-cycle limiting to avoid core saturation.

Key Specifications

Pinout & Package

UC3844AD8G4 is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, optimized for automated assembly and thermal performance in board-level power converters.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC3844D8, UC3844AD8G4 adds RoHS compliance and tape-and-reel delivery; compared with SG3525AN, it delivers integrated current sensing and UVLO hysteresis essential for robust, low-component-count flyback converters - making UC3844AD8G4 the optimal choice for cost-sensitive, isolated AC/DC applications.

Availability

UC3844AD8G4 is available at Aetrix Electronics and suitable for AC/DC adapters, industrial flyback PSUs, and battery-operated DC-DC converters requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for UC3844AD8G4 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 specializing in analog, embedded processing, and power management technologies, with decades of expertise in power conversion ICs.

The UCx84xA family was engineered specifically for cost-effective, high-reliability current-mode switch-mode power supplies - targeting off-line AC/DC adapters, industrial PSUs, and DC-DC modules where precision timing, low start-up current, and integrated protection are critical.

FAQ

What is the maximum operating frequency of the UC3844AD8G4?

The UC3844AD8G4 supports up to 500 kHz oscillator frequency, determined by external RT and CT components. Its trimmed 8.3 mA oscillator discharge current ensures stable timing accuracy across temperature and unit variation, enabling reliable high-frequency operation in compact power supplies without external frequency calibration.

Does the UC3844AD8G4 support duty cycles above 50%?

No, the UC3844AD8G4 enforces a hard limit of ≤50% maximum duty cycle due to internal architecture - unlike UC3842A/UC3843A variants. This is intentional for flyback and forward converters to prevent transformer core saturation; slope compensation is required if attempting higher effective duty cycles in specific topologies.

What is the purpose of the VREF pin on the UC3844AD8G4?

UC3844AD8G4's VREF pin delivers a precision 5.0 V ±1% output used to bias the RT/CT timing network, power optocoupler LEDs in isolated feedback loops, or supply auxiliary circuitry. It is short-circuit protected (~100 mA) and rated for ≤10 mA continuous load; a 1 µF high-frequency bypass capacitor is mandatory for stability.

How does the UC3844AD8G4 handle undervoltage lockout?

The UC3844AD8G4 features a dedicated UVLO circuit with 16 V turn-on and 10 V turn-off thresholds (6 V hysteresis). During UVLO, the OUTPUT pin is held low, the reference is disabled, and supply current drops to <0.5 mA - preventing parasitic MOSFET turn-on and ensuring clean, glitch-free startup in offline power supplies.

Can the UC3844AD8G4 directly drive a power MOSFET?

Yes, UC3844AD8G4's OUTPUT pin provides 1 A of peak sink/source current in a totem-pole configuration, enabling direct gate drive of medium-power MOSFETs (e.g., 400 V/2 A types) in sub-100W converters. A series gate resistor (typically 10–47 Ω) is required to control slew rate and suppress ringing, per TI's layout guidelines.