Texas Instruments UCC29950DR

Overview

UCC29950 from Texas Instruments is a CCM boost PFC and half-bridge LLC resonant combo controller in SOIC-16 package, delivering fixed 100-kHz PFC switching with dithering, 70–350 kHz LLC frequency range, true input power limiting independent of line voltage, and integrated X-cap discharge for <50 mW standby power in offline AC-to-DC server and industrial power supplies.

For engineers reviewing the UCC29950 datasheet, UCC29950 pinout, UCC29950 application, or UCC29950 equivalent, key selection considerations include its dual-stage control coordination, three-level LLC over-current protection, self-bias vs. auxiliary bias mode selection via MD_SEL/PS_ON, and internal PFC loop compensation eliminating external Type-II/III networks.

Technical Context

The UCC29950 implements a proprietary hybrid average/peak current control algorithm for the CCM boost PFC stage-using average current regulation for THD optimization while employing peak PFC_CS sensing to terminate each switching cycle. This eliminates sensitivity to inductor and bulk capacitor tolerances and enables full internal PFC loop compensation.

Its LLC control uses FB pin voltage to modulate switching frequency (70–350 kHz), dynamically adjusts dead time across load to extend ZVS range, and enforces hiccup-mode recovery after long faults (1.0 s) or short faults (100 ms). Protection includes AC line brownout detection (32 ms delay), PFC bus OVP/UVP, and differential AC1/AC2 sensing with 9.3-MΩ resistors.

Key Specifications

Pinout & Package

UCC29950 is housed in a standard SOIC-16 (D) package measuring 9.90 mm × 6.00 mm, optimized for surface-mount assembly and thermal dissipation in high-density power supplies.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar CCM PFC + LLC resonant controller applications.

Compared with UCC29951DR, the UCC29950 trades programmability for simplicity and cost; compared with NCP1654BD1R2G, it delivers tighter PFC-LLC coordination and lower BOM count but less stage-level flexibility.

Availability

UCC29950 is available at Aetrix Electronics and suitable for server power supplies, industrial DIN rail PSUs, and high-density adapters requiring stable component supply, long-term lifecycle support, and traceable sourcing for production programs.

Supply support for UCC29950 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 high-efficiency power conversion solutions.

The UCC29950 belongs to TI's AC/DC combo controller product line, engineered specifically for high-density, high-efficiency offline power supplies targeting 80 PLUS Bronze through Titanium certification levels.

FAQ

What is the primary function of the UCC29950?

The UCC29950 is a fully integrated combo controller that manages both a continuous conduction mode (CCM) boost power factor correction (PFC) stage and a half-bridge LLC resonant DC-to-DC stage in a single SOIC-16 device. It performs real-time coordination between the two stages-including shared protection, synchronized soft-start, and joint efficiency optimization-enabling compact, high-efficiency AC-to-DC power supplies without requiring external microcontrollers or discrete controllers. The UCC29950 handles all critical functions including PFC current regulation, LLC frequency modulation, gate drive outputs, and comprehensive fault management.

How does the UCC29950 achieve low standby power?

The UCC29950 achieves low standby power (<50 mW) through three integrated features: (1) active X-capacitor discharge circuitry that safely bleeds EMI filter energy within 1 second of AC removal; (2) depletion-mode MOSFET start-up via SUFG/SUFS pins, eliminating continuous power loss from traditional startup resistors; and (3) high-impedance AC line sensing (9.3-MΩ dividers) and VBULK sensing (30-MΩ upper resistor), minimizing quiescent current draw. These features collectively meet stringent 80 PLUS Gold and Titanium standby requirements without external components. The UCC29950 implements all three mechanisms natively, making low-power design achievable with minimal external circuitry.

What are the key differences between self-bias and auxiliary bias modes on the UCC29950?

In self-bias mode, the UCC29950 charges its VCC rail during startup using an external depletion-mode MOSFET controlled by SUFG/SUFS pins, then transitions to power from an auxiliary winding on the LLC transformer-eliminating static losses. In auxiliary bias mode, VCC is supplied externally (e.g., from a small auxiliary supply), and the MD_SEL/PS_ON pin serves as a digital enable signal: low voltage starts only the PFC stage, higher voltage enables both PFC and LLC. Self-bias reduces component count and improves light-load efficiency; auxiliary bias offers faster startup, better voltage regulation, and independent control of stage sequencing. The UCC29950 automatically configures internal logic based on MD_SEL/PS_ON state at power-up.

Does the UCC29950 require external compensation components for the PFC loop?

No, the UCC29950 does not require external compensation components for the PFC control loop. It integrates full Type-III compensation internally, leveraging its proprietary hybrid average/peak current control algorithm. This eliminates the need for external op-amps, resistors, and capacitors traditionally used to stabilize the PFC voltage and current loops. Engineers only need to set the PFC output voltage via the VBULK divider and configure current sensing gain via the PFC_CS resistor-significantly simplifying design, reducing BOM cost, and improving layout robustness. The UCC29950's internal compensation is factory-trimmed and temperature-compensated, ensuring stable performance across operating conditions.

What protection features does the UCC29950 provide for the LLC stage?

The UCC29950 provides multi-tiered protection for the LLC stage, including three-level over-current protection (OCP1/OCP2/OCP3) triggered by the LLC_CS pin, with distinct responses: OCP1 initiates hiccup mode for mild overloads, OCP2 triggers immediate shutdown for severe overloads, and OCP3 enforces 1-second lockout followed by automatic restart for sustained faults. Additional protections include FB pin overvoltage shutdown (>3.75 V), thermal shutdown at 125°C, and AC line brownout detection (32 ms delay) with 100 ms hold-up time. All protections are hardware-based with no firmware dependency, ensuring deterministic response. The UCC29950 also dynamically adjusts dead time to maintain ZVS across load, preventing hard-switching stress during transients.