Texas Instruments UC3855ADWTR

Overview

UC3855ADWTR from Texas Instruments is a high-frequency average current mode PFC controller IC designed for boost-type power factor correction preregulators. It delivers fixed-frequency control up to 500 kHz, integrates active snubbing (ZVT) for reduced MOSFET turn-on and diode recovery losses, features an inductor current synthesizer for single-current-transformer sensing, and includes a precision analog multiplier with line compensation for universal input operation. It operates across 0°C to 70°C and targets AC-DC front-end stages in industrial power supplies.

For engineers reviewing the UC3855ADWTR datasheet, UC3855ADWTR pinout, UC3855ADWTR application, or UC3855ADWTR equivalent, key selection criteria include its ZVT gate drive capability (±0.25 A continuous), 7.5 V ±1% reference accuracy, 2.5 MHz current amplifier bandwidth, and SOIC-20 package compatibility with standard PCB layout practices.

Technical Context

The UC3855ADWTR implements average current mode control using a wide-bandwidth (2.5 MHz) current amplifier and inductor current synthesizer that reconstructs the boost inductor waveform from a single current transformer signal. Its internal single-quadrant multiplier generates the current command by scaling VRMS², enabling stable line current programming without slope compensation.

It integrates dual gate drivers: a 1.5 A peak PFC switch driver (GTOUT) and a 0.75 A peak ZVT auxiliary switch driver (ZVTOUT), both supporting resonant soft-switching. The controller includes overvoltage protection with 7.66 V threshold and 400 mV hysteresis, UVLO with 15.5 V turn-on (A version), and a 1% 7.5 V reference with ±15 mV load regulation.

Key Specifications

Pinout & Package

UC3855ADWTR is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, 12.83 mm long, 2.65 mm max height, RoHS-compliant with NiPdAu lead finish and JEDEC MS-013 outline.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28070DR and ICE3PCS01G, UC3855ADWTR uniquely combines average current mode control, integrated ZVT gate drive, and current synthesis-enabling high-efficiency, low-EMI, 500 kHz PFC in a single SOIC-20 package without requiring phase interleaving or external snubber controllers.

Availability

UC3855ADWTR is available at Aetrix Electronics and suitable for industrial AC-DC power supplies, server front-end rectifiers, and medical equipment power modules requiring stable component supply and long-term design continuity.

Supply support for UC3855ADWTR 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 and industrial control solutions.

The UC3855 family was engineered specifically for high-efficiency, high-frequency boost PFC preregulators in commercial and industrial power supplies, emphasizing ZVT enablement, line-voltage feedforward, and noise-immune current sensing.

FAQ

What is the operating temperature range for UC3855ADWTR?

The UC3855ADWTR is rated for 0°C to +70°C ambient operation, consistent with its UC3855A designation. This commercial-grade range supports deployment in enclosed power supplies, server PSUs, and industrial equipment where airflow and heatsinking maintain junction temperatures within specification. The device's thermal derating begins above 70°C, and extended temperature variants (e.g., UC2855A) are not pin-compatible replacements.

Does UC3855ADWTR support zero-voltage switching (ZVS) for the main boost MOSFET?

No, UC3855ADWTR does not directly sense or control ZVS of the main boost MOSFET. It implements Zero Voltage Transition (ZVT) via the ZVTOUT driver and external auxiliary circuitry - which resonantly discharges the boost diode and main switch node prior to turn-on. ZVS of the main switch depends on external resonant tank design, not direct UC3855ADWTR ZVS sensing; the ZVS pin monitors drain voltage but only resets the ZVT latch.

Can UC3855ADWTR be used with resistive current sensing instead of a current transformer?

Yes, UC3855ADWTR supports both methods: a simple resistive shunt may be used at the CS pin for average current sensing, though this introduces conduction loss and noise sensitivity. The current synthesizer path (ION→CI→CS) is optimized for transformer-based sensing and delivers superior SNR and efficiency - especially above 500 W - but shunt-based designs remain viable for lower-power or cost-constrained implementations.

What is the purpose of the VRMS pin on UC3855ADWTR?

The VRMS pin on UC3855ADWTR accepts a DC voltage proportional to the RMS value of the rectified AC input (typically 1.5 V at low line, 4.7 V at high line). It feeds the internal analog multiplier to scale the current command by 1/VRMS², ensuring constant output power and near-unity power factor across universal input ranges (90–264 VAC) without software or external compensation.

Is UC3855ADWTR pin-compatible with UC2855ADWTR?

No, UC3855ADWTR and UC2855ADWTR are not pin-compatible due to differing operating temperature ranges (0°C–70°C vs. −40°C–85°C) and UVLO thresholds (15.5 V vs. 10.5 V for B variant), though they share identical SOIC-20 (DW) packaging and pinout. Electrical behavior, startup sequencing, and thermal validation differ - substitution requires full requalification of the PFC stage, including OVP timing, soft-start profile, and current loop stability.