Texas Instruments UC2844AQD

Overview

UC2844AQD from Texas Instruments is a current-mode PWM controller IC designed for off-line and DC-DC power converters, featuring 16 V UVLO turn-on threshold, <50% maximum duty cycle, and 500 kHz oscillator operation. It delivers high-current totem-pole output (±1 A), low start-up current (<0.5 mA), and internal 5.0 V ±1% bandgap reference - enabling compact, stable flyback and forward converter designs in automotive-grade temperature range (–40°C to 125°C).

For engineers reviewing the UC2844AQD datasheet, UC2844AQD pinout, UC2844AQD application, or UC2844AQD equivalent, key selection criteria include its fixed 50% duty-cycle limit, UVLO hysteresis (16 V ON / 10 V OFF), oscillator discharge current trim (8.3 mA typ), pulse-by-pulse current limiting, and SOIC-14 package compatibility with standard PCB layouts for industrial SMPS designs.

Technical Context

The UC2844AQD implements a current-mode control architecture with a toggle flip-flop that enforces ≤50% maximum duty cycle - critical for preventing transformer saturation in push-pull and half-bridge topologies. Its error amplifier provides 90 dB open-loop gain and 1 MHz unity-gain bandwidth, supporting precise voltage regulation via optocoupler feedback.

Oscillator frequency is set by external RT/CT components and internally divided by two to yield 500 kHz output switching frequency. The current sense path features 3.0 V/V gain and 300 ns delay, while UVLO ensures reliable startup and brownout recovery with 6 V hysteresis (16 V ON → 10 V OFF).

Key Specifications

Pinout & Package

UC2844AQD is supplied in a 14-pin SOIC (D package) with 1.27 mm pitch, 8.65 mm × 3.91 mm body size, and RoHS-compliant green finish (CU NIPDAU, MSL Level-1).

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC2844AD, UC2844AQD offers guaranteed operation down to –40°C and up to 125°C - essential for under-hood or factory-floor deployments - while TL494CN demands external circuitry to match UC2844AQD's integrated current-sense, reference, and protection functions, increasing design complexity and footprint.

Availability

UC2844AQD is available at Aetrix Electronics and suitable for AC-DC adapters, industrial DC-DC converters, automotive infotainment power supplies, and medical isolated auxiliary supplies requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for UC2844AQD 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 UC284xA family was engineered specifically for high-reliability current-mode switched-mode power supplies in automotive, industrial, and telecom infrastructure - emphasizing robust UVLO, precision timing, and integrated protection features.

FAQ

What is the maximum duty cycle supported by UC2844AQD?

The UC2844AQD supports a maximum duty cycle of less than 50%, enforced by an internal toggle flip-flop to prevent transformer saturation in push-pull and half-bridge topologies. This is a hard limit distinct from the UC2842AQD/UC2843AQD variants, which allow up to 100%. Designers must account for this constraint when selecting transformer turns ratio and output rectification scheme in UC2844AQD-based power supplies.

Does UC2844AQD require an external current sense resistor?

Yes, UC2844AQD requires an external current sense resistor placed in series with the primary-side switch to generate the voltage signal applied to the ISENSE pin. The device compares this signal against a 1.0 V threshold to implement pulse-by-pulse current limiting. Typical values range from 0.1 Ω to 1 Ω depending on peak primary current, and layout must minimize noise coupling using short, Kelvin-connected traces.

Can UC2844AQD operate without the VREF pin connected?

No, UC2844AQD requires the VREF pin (Pin 8) to be externally decoupled with a 0.1 µF ceramic capacitor to ground, even if the 5.0 V reference is not used by external circuitry. This capacitor stabilizes the internal bandgap reference and oscillator timing network. Leaving VREF floating or un-decoupled causes erratic frequency behavior and potential startup failure in UC2844AQD systems.

What is the purpose of the VC pin (Pin 11) on UC2844AQD?

The VC pin on UC2844AQD provides access to the internal voltage-controlled oscillator bias node and enables automatic feed-forward compensation. By connecting a resistor-capacitor network from VC to VREF, designers inject line-voltage proportional correction into the oscillator ramp, improving regulation accuracy and transient response during input voltage variations - a key advantage over basic voltage-mode controllers.

Is UC2844AQD pin-compatible with UC2842AQD or UC2843AQD?

Yes, UC2844AQD is pin-for-pin compatible with UC2842AQD, UC2843AQD, and UC2845AQD in both SOIC-8 and SOIC-14 packages. However, functional differences exist: UC2844AQD and UC2845AQD share identical UVLO thresholds (16 V ON / 10 V OFF) and ≤50% duty cycle, whereas UC2842AQD/UC2843AQD support ≤100% duty cycle and different UVLO points. Swapping requires verifying duty-cycle and startup voltage requirements.