Texas Instruments UCC38501N

Overview

UCC38501N from Texas Instruments is a dual-stage power factor correction (PFC) and DC-DC controller IC for AC-DC power supplies, integrating average-current-mode PFC control with peak-current-mode second-stage PWM control. It delivers near-unity power factor, programmable 100 kHz oscillator frequency, 7.5 V internal reference, and 10.5 V/10 V narrow UVLO threshold optimized for fixed-bias operation. Used in universal-input offline power converters delivering regulated 12 V/100 W output.

For engineers reviewing the UCC38501N datasheet, UCC38501N pinout, UCC38501N application, or UCC38501N equivalent, key selection criteria include its dual-stage synchronization capability, leading-edge PFC + trailing-edge PWM modulation scheme, feedforward line regulation, soft-start sequencing, and compatibility with boost PFC + forward DC-DC topologies.

Technical Context

The UCC38501N implements a two-stage control architecture: the PFC stage uses average current-mode control with IAC-based line voltage sensing and VFF feedforward to maintain constant input power across 85–265 V_RMS input range; the second stage employs peak current-mode control with external error signal injection via VERR and 50% maximum duty cycle clamping for transformer reset.

It features synchronized start-up where the DC-DC stage remains disabled until the PFC output reaches ≥90% of nominal (346.5 V for 385 V bulk), followed by controlled SS2 soft-start; shutdown occurs if PFC output falls below 74% of nominal, ensuring safe sequencing and stress reduction during brownout conditions.

Key Specifications

Pinout & Package

UCC38501N is housed in a 20-pin plastic DIP (N) package with 0.3-inch body width and through-hole mounting. Pin assignments are fully defined per TI SLUS419C Rev. November 2001.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28501N, the UCC38501N offers lower-cost commercial-temperature qualification and simplified thermal design; compared with UCC38501DW, it provides through-hole mechanical robustness and easier prototyping, though requiring manual soldering.

Availability

UCC38501N is available at Aetrix Electronics and suitable for industrial power supplies, medical AC-DC adapters, and server auxiliary power systems requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for UCC38501N 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 technologies, with decades of expertise in power conversion IC design.

The UCC3850x product line was engineered specifically for cost-sensitive, high-efficiency two-stage AC-DC power supplies targeting universal-input offline applications from 50 W to 300 W.

FAQ

What is the operating temperature range for the UCC38501N?

The UCC38501N is specified for operation from 0°C to 70°C ambient temperature. This commercial-grade rating distinguishes it from the industrial-grade UCC28501N (–40°C to 85°C). Thermal derating is not required within this range, and the device's junction temperature remains within safe limits under typical 12 V/100 W application conditions with standard heatsinking. The UCC38501N datasheet confirms TJ = –55°C to 125°C absolute maximum, but functional operation is guaranteed only across the 0°C–70°C ambient window.

How does the UCC38501N implement power factor correction?

The UCC38501N implements active PFC using average current-mode control. It senses instantaneous line current via the IAC pin, generates a feedforward voltage (VFF) proportional to RMS line voltage, and shapes the boost switch duty cycle using a high-linearity analog multiplier. This forces the input current waveform to closely follow the sinusoidal input voltage, achieving near-unity power factor (>0.99 at full load). The UCC38501N also incorporates accurate power limiting and overvoltage protection to ensure stable regulation across universal AC inputs.

What is the purpose of the VERR pin on the UCC38501N?

The VERR pin on the UCC38501N accepts an externally generated error signal-typically from a secondary-side TL431/shunt regulator fed via optocoupler-to regulate the DC-DC stage output voltage. Internally, VERR is clamped to 4.5 V to enforce ≤50% duty cycle on GT2, ensuring safe transformer reset in forward converter topologies. This architecture decouples primary-side control from secondary-side feedback, enabling precise isolation and eliminating the need for an internal error amplifier in the UCC38501N.

Can the UCC38501N be used in single-stage PFC designs?

No, the UCC38501N is designed exclusively for two-stage architectures combining a PFC preregulator and an isolated DC-DC converter. Its block diagram, pin functions (e.g., separate GT1/GT2 drivers, VERR input, SS2 soft-start), and internal UVLO2 sequencing logic assume coordinated operation between boost and forward/flyback stages. It lacks the integrated error amplifier, bias generation, and control loop structures needed for single-stage PFC flyback or buck-boost topologies. For those applications, TI recommends the UCC28051 or UCC28070.

What are the key differences between UCC38501N and UCC28501N?

The UCC38501N and UCC28501N share identical electrical specifications, pinout, and functional architecture-but differ in temperature rating and UVLO hysteresis. The UCC38501N is rated for 0°C to 70°C and has 0.5 V UVLO hysteresis, while the UCC28501N operates from –40°C to 85°C with 0.3 V hysteresis. Both use the same 10.5 V/10 V UVLO thresholds and are drop-in replacements in circuits where temperature and hysteresis margins permit. The UCC38501N is optimized for cost-sensitive commercial applications.