Texas Instruments UC2844D8

Overview

UC2844D8 from Texas Instruments is a fixed-frequency current-mode PWM controller IC designed for off-line AC-DC power supplies. It features 16 V turn-on / 10 V turn-off UVLO hysteresis, ≤1 mA start-up current, 50% maximum duty cycle, 5 V internal reference, and up to 500 kHz oscillator frequency. It drives N-channel MOSFETs directly via a totem-pole output stage capable of ±1 A peak current.

For engineers reviewing the UC2844D8 datasheet, UC2844D8 pinout, UC2844D8 application, or UC2844D8 equivalent, key selection criteria include its 50% max duty cycle (vs. 100% in UC2842/3), UVLO thresholds optimized for unregulated high-voltage inputs, SOIC-8 package footprint, and compatibility with transformer-coupled flyback and forward converter topologies requiring cycle-skipping operation.

Technical Context

The UC2844D8 implements current-mode control using an internal PWM comparator that compares sensed primary current (via ISENSE) against the error amplifier output (COMP). Its oscillator uses RT/CT pin with external R–C network to set frequency, where f_SW = f_OSC/2 due to integrated toggle flip-flop - a defining architectural difference from UC2842/3.

UVLO circuitry ensures reliable start-up only when VCC ≥ 16 V and maintains latched operation until VCC drops below 10 V, preventing erratic switching during brown-out conditions. The 5-V bandgap reference (VREF) is internally trimmed to ±2% and supplies timing current and error amplifier bias, supporting stable closed-loop regulation across –40°C to 85°C.

Key Specifications

Pinout & Package

UC2844D8 is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, with gull-wing leads and standard JEDEC MS-012AC outline.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC2844N8 and UC3844D8, the UC2844D8 uniquely balances industrial temperature operation, surface-mount manufacturability, and proven thermal performance in SOIC-8 - making it the optimal choice for volume production of robust off-line power supplies.

Availability

UC2844D8 is available at Aetrix Electronics and suitable for AC-DC flyback adapters, industrial DC-DC forward converters, and offline LED driver power supplies requiring stable component supply and long-term design continuity.

Supply support for UC2844D8 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 over 50 years of power IC innovation.

The UC284x family was engineered specifically for cost-effective, high-reliability current-mode switching power supplies - targeting off-line AC-DC and isolated DC-DC converter applications where minimal external components and robust protection are essential.

FAQ

What is the maximum duty cycle supported by UC2844D8?

The UC2844D8 supports a maximum duty cycle of 50%, enforced by an internal toggle flip-flop that blanks the OUTPUT every other oscillator cycle. This distinguishes it from UC2842/3 (100% max duty) and is critical for safe operation in flyback converters where excessive conduction time risks transformer saturation. The 50% limit is a hard architectural feature, not a configuration option.

Does UC2844D8 require an external oscillator component?

Yes, UC2844D8 requires external timing components: a resistor (R_RT) connected between VREF and RT/CT, and a capacitor (C_CT) from RT/CT to GROUND. These set the oscillator frequency using f_OSC = 1.72/(R_RT × C_CT). The OUTPUT switching frequency is exactly half f_OSC due to the internal toggle logic - no crystal or external clock source is needed or supported.

How does the UVLO behavior of UC2844D8 differ from UC2842D8?

UC2844D8 and UC2842D8 share identical UVLO thresholds: turn-on at 16 V and turn-off at 10 V, providing 6 V hysteresis. This is confirmed in TI's device comparison table and electrical specifications. The key functional difference lies in maximum duty cycle (50% vs. 100%) and oscillator-to-output frequency division - not UVLO behavior. Both are optimized for off-line applications requiring high-noise immunity.

Can UC2844D8 drive a P-channel MOSFET directly?

No, UC2844D8 is designed to drive N-channel MOSFETs only. Its OUTPUT stage is a totem-pole configured to sink current when active low and source current when active high - ideal for pulling an N-MOSFET gate to ground or VCC. Driving a P-channel device would require level-shifting circuitry or an external driver, as UC2844D8 lacks high-side gate drive capability or bootstrap support.

What is the purpose of the VREF pin on UC2844D8?

The VREF pin on UC2844D8 provides a stable, internally trimmed 5 V reference used for two critical functions: (1) supplying the charging current to the RT/CT timing capacitor via the external resistor, and (2) serving as the precision reference for the error amplifier's feedback network. It must be bypassed with ≥0.1 µF ceramic capacitor to GROUND, placed adjacent to the pin, to ensure oscillator stability and regulation accuracy.