Texas Instruments UC3842AD8TRG4

Overview

UC3842AD8TRG4 from Texas Instruments is a current-mode PWM controller IC designed for off-line and DC-DC switch-mode power supplies. It features 16 V UVLO turn-on threshold, 8.3 mA trimmed oscillator discharge current, 1 A totem-pole output drive, ±1 A output current capability, and supports up to 500 kHz switching frequency in flyback and forward converter topologies.

For engineers reviewing the UC3842AD8TRG4 datasheet, UC3842AD8TRG4 pinout, UC3842AD8TRG4 application, or UC3842AD8TRG4 equivalent, key selection criteria include startup current (<0.5 mA), pulse-by-pulse current limiting, undervoltage lockout hysteresis, internal 5 V reference accuracy (±1%), and SOIC-8 package compatibility with legacy UC3842 designs.

Technical Context

The UC3842AD8TRG4 implements peak-current-mode control using an internal error amplifier (80 dB open-loop gain, 1 MHz unity-gain bandwidth) and a dedicated current-sense comparator clamped at 1 V. Its oscillator uses RT/CT programming with trimmed discharge current (7.6–8.8 mA) to ensure stable duty-cycle control across temperature and supply voltage.

During undervoltage lockout, the device draws only 0.3–0.5 mA start-up current and forces OUTPUT low while sinking ≥10 mA at ≤1.2 V - a critical feature for reliable high-voltage bootstrap startup in AC-DC adapters. The 5 V bandgap reference (±1% over 0°C to 70°C) supplies both internal comparators and external feedback circuitry.

Key Specifications

Pinout & Package

UC3842AD8TRG4 is housed in an 8-pin SOIC (D) package measuring 4.90 mm × 6.00 mm, optimized for surface-mount assembly and thermal performance in power supply PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UC3842BD1R2G and NCP1014DR2G, UC3842AD8TRG4 offers balanced trade-offs: full programmability (RT/CT), robust 1 A drive, and proven reliability in mid-power (20–100 W) industrial and adapter designs - without sacrificing layout simplicity or thermal performance.

Availability

UC3842AD8TRG4 is available at Aetrix Electronics and suitable for AC-DC adapters, flyback power supplies, and industrial DC-DC converters requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for UC3842AD8TRG4 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 for industrial, automotive, and consumer applications.

The UCx84xA product line was engineered specifically for cost-effective, high-reliability current-mode switch-mode power supplies - targeting off-line AC-DC conversion, isolated DC-DC modules, and battery-operated power systems where startup efficiency and fault resilience are critical.

FAQ

What is the maximum operating temperature range for UC3842AD8TRG4?

The UC3842AD8TRG4 is rated for 0°C to 70°C ambient operating temperature, matching the UC384xA family specification. This range supports commercial and industrial power supply environments but excludes extended-temperature applications covered by UC284xA (–40°C to 85°C) or UC184xA (–55°C to 125°C). Derating may be required above 60°C depending on PCB copper area and airflow. UC3842AD8TRG4 thermal resistance (R_θJA) is 117.4°C/W in SOIC-8 package.

Does UC3842AD8TRG4 support duty cycles above 50%?

UC3842AD8TRG4 supports up to 100% duty cycle in its base configuration, as confirmed by the device comparison table listing "<100%" for UC3842A/UC3843A variants. However, stable operation above 50% requires external slope compensation injected into the ISENSE node to prevent subharmonic oscillation - a standard practice in current-mode controllers. The internal oscillator and current-sense architecture fully support this implementation per TI application notes.

How does the UVLO behavior of UC3842AD8TRG4 differ from the original UC3842?

UC3842AD8TRG4 features improved UVLO with 14.5–17.5 V turn-on threshold and 8.5–11.5 V turn-off threshold (1.5–2.5 V hysteresis), versus the original UC3842's 16 V/10 V. During UVLO, UC3842AD8TRG4 sinks ≥10 mA at ≤1.2 V on OUTPUT - significantly stronger than the legacy part - preventing parasitic MOSFET turn-on due to Miller effect during startup. This enhances reliability in high-voltage bootstrap circuits.

Can UC3842AD8TRG4 replace UC3842N in a through-hole design?

No - UC3842AD8TRG4 is a surface-mount SOIC-8 device and is not a direct replacement for through-hole PDIP-8 UC3842N. While electrically identical in function and pinout, the package change requires PCB redesign. For drop-in replacement, use UC3842AN (PDIP-8) or UC3842AD8 (SOIC-8 without tape-and-reel suffix). Always verify VREF accuracy, oscillator discharge current, and UVLO thresholds match the legacy design's requirements before substitution.

What is the recommended minimum VREF bypass capacitance for UC3842AD8TRG4?

Texas Instruments specifies a minimum 1 µF high-frequency ceramic capacitor directly at the VREF pin of UC3842AD8TRG4 to suppress noise and ensure reference stability. This capacitor must be placed adjacent to the pin with short traces. Additionally, the VCC bypass capacitor should be at least 10× larger than the VREF capacitor (i.e., ≥10 µF) and located near the VCC pin to maintain gate driver stability and reduce supply ripple coupling into the oscillator and error amplifier.