Texas Instruments UC3843AD8TRG4

Overview

UC3843AD8TRG4 from Texas Instruments is a current-mode PWM controller IC designed for off-line and DC-DC switch-mode power supplies. It features 8.3 mA trimmed oscillator discharge current, <0.5 mA start-up current, undervoltage lockout with 8.4 V turn-on/7.6 V turn-off hysteresis, 1 A totem-pole output drive, and operates up to 500 kHz - enabling compact, high-efficiency flyback and forward converter designs in industrial PSUs.

For engineers reviewing the UC3843AD8TRG4 datasheet, UC3843AD8TRG4 pinout, UC3843AD8TRG4 application, or UC3843AD8TRG4 equivalent, key selection criteria include its 8-pin SOIC (D) package, peak-current-mode control architecture, internal 5 V reference with ±1% tolerance over temperature, pulse-by-pulse current limiting, and compatibility with WEBENCH® Power Designer for rapid custom SMPS design.

Technical Context

The UC3843AD8TRG4 implements fixed-frequency peak-current-mode control using an internal oscillator with programmable RT/CT timing network, a 1-MHz error amplifier with 80 dB open-loop gain, and a current-sense comparator clamping at 1 V. Its UVLO circuit ensures controlled startup with 8.4 V activation and 7.6 V hysteresis, while the totem-pole output delivers ±1 A gate drive capable of directly driving MOSFETs in low-to-mid-power converters.

This device belongs to the UCx84xA family - a pin-for-pin enhanced revision of the legacy UCx84x series - with improved oscillator discharge current trimming, lower start-up current, and higher output sink capability during UVLO (≥10 mA at <1.2 V). It supports duty cycles up to 100% and is optimized for universal-input AC-DC adapters, battery-operated DC-DC modules, and industrial power supplies requiring stable regulation under line and load transients.

Key Specifications

Pinout & Package

UC3843AD8TRG4 is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, with surface-mount footprint and standard JEDEC MS-012AC dimensions.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC3843BD8TRG4, the UC3843AD8TRG4 trades minor reference and oscillator tolerances for broader availability and lower cost in volume production; versus NCP1014ST100T3G, it provides full external component control and scalability beyond 15 W, making it suitable for mid-power industrial and battery-fed designs where layout and thermal management are prioritized over integration density.

Availability

UC3843AD8TRG4 is available at Aetrix Electronics and suitable for AC-DC adapters, isolated DC-DC modules, and industrial power supply units requiring stable component supply, long-term lifecycle support, and consistent parametric performance across manufacturing lots.

Supply support for UC3843AD8TRG4 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, embedded processing, and power management technologies, with decades of leadership in power conversion ICs.

The UCx84xA product line was engineered specifically for cost-sensitive, high-reliability current-mode switch-mode power supplies - targeting off-line AC-DC, battery-fed DC-DC, and industrial PSU applications where predictable startup, robust current limiting, and stable reference performance are essential.

FAQ

What is the operating temperature range for UC3843AD8TRG4?

The UC3843AD8TRG4 is specified for an operating free-air temperature range of 0°C to 70°C, aligning with the UC384xA family classification. This makes it suitable for commercial and industrial indoor environments but not extended-temperature applications like automotive under-hood or military-grade deployments. The device's thermal metrics - including RθJA = 117.4°C/W for the SOIC-8 package - require appropriate PCB copper area and airflow to maintain junction temperature within the 150°C absolute maximum limit during continuous operation.

Does UC3843AD8TRG4 support duty cycles above 50%?

Yes, UC3843AD8TRG4 supports up to 100% duty cycle, unlike UC3844A/UC3845A variants limited to ≤50%. This capability is enabled by its UCx842A/UCx843A functional group designation and is confirmed in the Device Comparison Table and Section 6.3.5 of the datasheet. For applications requiring >50% duty cycle - such as forward converters or low-input-voltage flybacks - slope compensation via resistive summation of the oscillator ramp into the ISENSE node is recommended to prevent subharmonic oscillation.

How does the UVLO behavior of UC3843AD8TRG4 differ from UC3842A?

UC3843AD8TRG4 has an 8.4 V turn-on threshold and 7.6 V turn-off hysteresis, whereas UC3842A uses 16 V/10 V. This narrower hysteresis is optimized for DC-DC applications with regulated input rails, allowing faster, more stable startup under varying bias conditions. During UVLO, UC3843AD8TRG4's OUTPUT pin remains low and its VREF stays inactive, while the IC draws only 0.3–0.5 mA - significantly less than legacy UCx84x devices - reducing startup resistor dissipation in battery or auxiliary-winding powered systems.

Can UC3843AD8TRG4 drive a MOSFET directly without an external gate driver?

Yes, UC3843AD8TRG4 can drive medium-power MOSFETs directly via its OUTPUT pin, which sources and sinks up to ±1 A with 25–150 ns rise/fall times into 1 nF capacitive load. This eliminates external drivers in designs with MOSFETs having total gate charge ≤20 nC (e.g., IRF540N, FDP5800). For higher gate charge devices or layouts with long traces, a small series gate resistor (e.g., 10 Ω) is recommended to damp ringing and reduce EMI, while preserving switching speed and efficiency.

What is the purpose of the VREF pin on UC3843AD8TRG4, and how should it be decoupled?

The VREF pin on UC3843AD8TRG4 delivers a precision 5.0 V ±1% reference used for internal comparators and external feedback scaling. It must supply no more than 10 mA and is short-circuit protected at ~100 mA. To ensure stability and low noise, TI specifies a minimum 1 µF high-frequency ceramic capacitor (X7R or better) placed as close as possible to the VREF and GND pins. The VCC bypass capacitor should be ≥10× larger than the VREF capacitor to prevent coupling of switching noise into the reference path.