Texas Instruments UC2844NG4

Overview

UC2844NG4 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, ≤50% maximum duty cycle, 5 V internal reference (±2%), and up to 500 kHz oscillator frequency. The device drives N-channel MOSFETs via a 1 A peak totem-pole output and supports pulse-by-pulse current limiting in flyback and forward converter topologies.

For engineers reviewing the UC2844NG4 datasheet, UC2844NG4 pinout, UC2844NG4 application, or UC2844NG4 equivalent, key selection criteria include its 50% max duty cycle limitation, UVLO thresholds optimized for unregulated high-voltage inputs, low start-up current (<1 mA), and compatibility with standard SOIC-8 PCB footprints.

Technical Context

The UC2844NG4 implements current-mode control using an internal PWM comparator that terminates switch conduction based on ISENSE voltage, with built-in slope compensation capability via external ramp injection. Its oscillator uses RT/CT pin with R_RT–C_CT network to set f_OSC, while OUTPUT switching frequency is exactly half f_OSC due to an integrated toggle flip-flop.

This architecture enforces strict 0–50% duty cycle operation and eliminates subharmonic oscillation without external compensation. The error amplifier delivers 90 dB open-loop gain and 1 MHz unity-gain bandwidth, with COMP pin capable of sourcing/sinking current and commanding zero duty cycle when pulled to ground.

Key Specifications

Pinout & Package

UC2844NG4 is housed in an 8-pin SOIC package (D package), 4.90 mm × 6.00 mm body size with standard 1.27 mm pitch. Pin functions are validated per TI SLUS223H Rev. October 2024.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC2844NG4, UC2844D offers identical performance with standard RoHS compliance, while UC3844N sacrifices temperature range for PDIP packaging - making UC2844NG4 the optimal choice for industrial-grade, surface-mount flyback controllers requiring guaranteed –40°C startup.

Availability

UC2844NG4 is available at Aetrix Electronics and suitable for AC-DC flyback adapters, industrial auxiliary supplies, and offline LED drivers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for UC2844NG4 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 company specializing in analog and embedded processing technologies, with leadership in power management ICs since the 1970s.

The UC284x product line was engineered specifically for cost-sensitive, high-reliability off-line and DC-DC current-mode power supplies - delivering integrated UVLO, precision reference, and robust gate drive in minimal external-component configurations.

FAQ

What is the maximum switching frequency supported by UC2844NG4?

The UC2844NG4 oscillator operates from 100 kHz to 500 kHz. Because the OUTPUT pin toggles at half the oscillator frequency due to its internal toggle flip-flop, the effective PWM switching frequency range is 50–250 kHz. This is confirmed in Section 6.5 of the SLUS223H datasheet, where f_OSC initial accuracy is specified at 47–57 kHz for test conditions - scaling linearly with RT/CT values.

Does UC2844NG4 support duty cycles above 50%?

No. The UC2844NG4 enforces a hard 50% maximum duty cycle via an internal toggle flip-flop that blanks the OUTPUT every other oscillator cycle. This architectural feature is intrinsic to all UCx844/UCx845 variants and is explicitly documented in Figures 7-2 and Section 7.3.1.6 of the datasheet. Attempting to exceed 50% results in immediate cycle skipping.

How does the UVLO behavior of UC2844NG4 differ from UC2842NG4?

The UC2844NG4 has 16 V turn-on and 10 V turn-off UVLO thresholds, providing 6 V hysteresis optimized for noisy, unregulated rectified AC inputs. In contrast, UC2842NG4 shares these same thresholds - both belong to the "2/4" subgroup. The UC2843/UC2845 variants use 8.4 V / 7.6 V thresholds instead, as clarified in Table 4 and Section 7.1 of the UCx84x datasheet.

Can UC2844NG4 be used in voltage-mode control configurations?

Yes. Although designed for current-mode control, the UC2844NG4 supports voltage-mode operation by injecting a sawtooth ramp onto the ISENSE pin - overriding the current-sense comparator's function. Section 7.3.1.3 confirms this capability, noting that "a voltage ramp can be applied to this pin to run the device with a voltage-mode control configuration." The internal gain remains 3 V/V regardless of mode.

What is the purpose of the VC pin, and is it present on UC2844NG4?

The VC pin provides a dedicated bias supply for the output gate driver stage and appears only on 14-pin and 20-pin UCx84x packages (e.g., SOIC-14, LCCC-20). The UC2844NG4 is an 8-pin SOIC device and does not include the VC pin - its gate driver is biased directly from VCC, as stated in Table 5-1 and Section 7.3.1.6 of the datasheet.