Texas Instruments UCC38502DW

Overview

UCC38502DW from Texas Instruments is a dual-stage active power factor correction (PFC) and DC-DC controller IC for offline AC-DC power supplies. It integrates average-current-mode PFC control with peak-current-mode downstream PWM, supports 85–265 V_RMS universal input, delivers near-unity power factor (>0.99), and features programmable 80–120 kHz oscillator frequency, 16.5 V/10 V wide UVLO threshold, and 50% max duty cycle clamp on GT2.

For engineers reviewing the UCC38502DW datasheet, UCC38502DW pinout, UCC38502DW application, or UCC38502DW equivalent, this page provides verified technical context, validated pin functions, confirmed operating parameters, and real-world design implications for two-stage PFC+forward converter systems requiring coordinated soft-start, feedforward line regulation, and bulk-capacitor ripple reduction.

Technical Context

The UCC38502DW implements leading-edge modulation on GT1 for the boost PFC stage and trailing-edge synchronized modulation on GT2 for the isolated DC-DC stage-minimizing switch overlap to reduce bulk capacitor ripple current. Its analog multiplier accepts IAC current input and uses VFF (derived from IAC via external RC filter) to normalize line-voltage variation, enabling constant input power across 3:1 input range without high-voltage sensing components.

PFC regulation relies on average-current-mode control using CAOUT feedback from ISENSE1/MOUT, while the second stage uses external error signal injected at VERR with internal 4.5 V clamp to enforce ≤50% duty cycle. UVLO2 thresholds are configured for wide-range operation (6.75 V turn-on, 3.0 V hysteresis), allowing PWM activation down to 50% of nominal bulk voltage-critical for brownout resilience in industrial AC-DC systems.

Key Specifications

Pinout & Package

UCC38502DW is housed in a 20-pin SOIC (DW) package with 0.65 mm pitch, 12.8 mm × 7.5 mm body, and exposed thermal pad (not electrically connected). Pin assignments follow TI's standard top-view layout for DW packages.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-stage PFC+PWM controller applications.

Compared with UCC28502DW, the UCC38502DW offers lower cost and smaller board area but sacrifices extended temperature capability; compared with UCC38502N, it delivers superior thermal performance and automated assembly compatibility at the expense of through-hole mounting flexibility.

Availability

UCC38502DW is available at Aetrix Electronics and suitable for server power supplies, industrial AC-DC adapters, and medical equipment PSUs requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for UCC38502DW 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 ICs, with decades of expertise in power conversion and energy-efficient system design.

The UCC3850x product line was designed specifically for cost-sensitive, high-efficiency two-stage AC-DC power supplies targeting commercial and light-industrial applications where integrated PFC+PWM control reduces system complexity and improves reliability.

FAQ

What is the primary function of the UCC38502DW in an AC-DC power supply?

The UCC38502DW serves as a dual-function controller that manages both the active power factor correction (PFC) boost stage and the downstream isolated DC-DC converter (e.g., forward or flyback) in a single IC. It performs average-current-mode control for PFC and peak-current-mode control for the second stage, coordinating start-up, shutdown, and ripple minimization. The UCC38502DW integrates all necessary analog blocks-including multiplier, error amplifiers, oscillators, and gate drivers-to eliminate discrete controllers and reduce system-level design effort.

How does the UCC38502DW achieve near-unity power factor?

The UCC38502DW achieves near-unity power factor (>0.99) by implementing average-current-mode control: it shapes the AC input line current waveform to match the AC input voltage using a high-linearity analog multiplier fed by IAC current and VFF voltage. The VFF signal-generated by mirroring IAC through an external RC filter-normalizes for RMS line voltage variation, ensuring constant input power across 85–265 V_RMS. This eliminates the need for high-voltage resistive dividers and enables low-distortion current tracking without digital computation. The UCC38502DW's low-offset current amplifier and precision 7.5 V reference further enhance accuracy.

What is the purpose of the VERR pin on the UCC38502DW?

The VERR pin on the UCC38502DW accepts an externally generated error signal-typically from a secondary-side optocoupler amplifier-to regulate the isolated DC-DC stage output voltage. Internally, the UCC38502DW applies a 4.5 V clamp to VERR, which directly limits GT2 duty cycle to ≤50% to guarantee safe transformer reset in forward or flyback topologies. This architecture decouples regulation from primary-side sensing, enabling tight output tolerance and isolation compliance. Unlike integrated error amplifiers, VERR allows full flexibility in compensation design and supports both voltage- and current-mode configurations depending on how the external ramp is applied to ISENSE2.

Can the UCC38502DW operate with a 230 V_RMS input only, or is universal input mandatory?

The UCC38502DW is fully compatible with fixed 230 V_RMS inputs and does not require universal 85–265 V_RMS operation. Its feedforward architecture (VFF derived from IAC) automatically adapts to any RMS line voltage within its absolute maximum ratings. For 230 V-only designs, the external RC filter on VFF can be optimized for reduced 120 Hz ripple, and UVLO thresholds remain valid (16.5 V/10 V). The UCC38502DW's 0°C to 70°C rating and SOIC-DW package make it well-suited for European mains-powered equipment where thermal margin and compact layout are priorities. No configuration changes are needed versus universal-input implementations.

What protection features are built into the UCC38502DW?

The UCC38502DW integrates multiple hardware-based protections: PFC overvoltage protection (OVP/ENBL window comparator), zero-power detection (0.33 V VAOUT threshold), peak current limiting (PKLMT with 0 V reference), and dual-stage undervoltage lockout (UVLO and UVLO2). UVLO2 has 3.0 V hysteresis to prevent PWM chattering during brownouts, and the SS2 pin enables fast discharge on fault. All protections act independently and immediately-no firmware or external logic required. These features ensure robust operation in unstable grid environments and prevent catastrophic failure during startup, overload, or AC dropout. The UCC38502DW's design inherently limits stress on external MOSFETs and bulk capacitors.