Texas Instruments UC3844AN

Overview

UC3844AN from STMicroelectronics is a high-performance current-mode PWM controller IC designed for fixed-frequency DC-DC and off-line power supplies. It features 500 kHz operation, internal toggle flip-flop limiting max duty cycle to <50%, trimmed 5 V reference (±2%), under-voltage lockout (16 V on / 10 V off), and ±1 A totem-pole output capable of directly driving N-channel MOSFETs in flyback or forward converters.

For engineers reviewing the UC3844AN datasheet, UC3844AN pinout, UC3844AN application, or UC3844AN equivalent, this device is selected for cost-sensitive, isolated AC-DC adapters, industrial auxiliary supplies, and low-power offline SMPS where precise current-mode control, latch protection, and minimal external components are required.

Technical Context

The UC3844AN implements current-mode control via a high-speed current-sense comparator with 3 V/V gain and 150 ns propagation delay, synchronized to an internally trimmed oscillator whose frequency (47–57 kHz typical) is set by RT/CT. Its error amplifier provides 90 dB open-loop gain and 1 MHz unity-gain bandwidth for stable loop compensation.

Under-voltage lockout includes hysteresis (16 V turn-on, 10 V turn-off), and the internal toggle flip-flop ensures every other clock cycle blanks the output - enforcing ≤50% maximum duty cycle without external circuitry. The 5 V reference is trimmed to ±2% over temperature and load, with 0.2 mV/°C stability.

Key Specifications

Pinout & Package

DIP-8 package (0.300" wide body, through-hole mounting) with standard lead pitch (2.54 mm), rated for 1.25 W power dissipation at T_amb ≤ 25 °C and junction temperature range –40 to +150 °C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC3844BD1, the UC3844AN offers lower thermal resistance and through-hole manufacturability; versus TL494CN, it delivers integrated current-mode control with fewer external components but lacks dual-output flexibility.

Availability

UC3844AN is available at Aetrix Electronics and suitable for AC-DC adapters, industrial auxiliary supplies, LED drivers, and telecom DC-DC bricks requiring stable component supply across extended production lifecycles.

Supply support for UC3844AN 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, delivering analog, microcontroller, power, and automotive ICs with emphasis on industrial and power conversion reliability.

The UC384x family was developed specifically for cost-effective, high-efficiency current-mode switch-mode power supplies - targeting off-line and DC-DC applications where minimal external parts and robust fault protection are essential.

FAQ

What is the maximum recommended switching frequency for UC3844AN?

The UC3844AN supports oscillator frequencies up to 500 kHz with appropriate RT/CT values, though its typical operating range is 47–57 kHz per datasheet characterization. At higher frequencies, gate drive rise/fall times (50–150 ns) and current-sense propagation delay (150–300 ns) become limiting factors for stable current-mode control and minimum on-time accuracy.

Can UC3844AN be used in boost converter topologies?

Yes - UC3844AN is commonly used in boost configurations, especially with continuous conduction mode (CCM). Its current-mode architecture provides inherent cycle-by-cycle protection, and the 5 V reference enables precise feedback scaling. However, external slope compensation is required for CCM stability, as noted in Figure 20 of the datasheet.

How does the internal toggle flip-flop affect duty cycle in UC3844AN?

The internal toggle flip-flop forces the OUTPUT pin to remain low every other clock cycle, limiting maximum duty cycle to <50%. This eliminates external duty-cycle clamping circuits and prevents transformer saturation in push-pull or half-bridge topologies - a key differentiator from UC3842A/UC3843A variants.

Is UC3844AN compatible with UC3842AN in the same PCB footprint?

No - although both use DIP-8 packages, UC3844AN and UC3842AN differ in UVLO thresholds (16 V/10 V vs. 16 V/10 V same), but critically, UC3842AN supports up to 100% duty cycle while UC3844AN is limited to <50%. Swapping them risks loss of regulation or transformer saturation unless circuit timing and feedback are redesigned.