Texas Instruments UCC28517N

Overview

UCC28517N from Texas Instruments is a dual-stage combination controller integrating average-current-mode PFC and peak-current-mode PWM control in a single 20-pin PDIP package. It delivers 2-A source / 3-A sink gate drive for both stages, supports 1:2 PFC:PWM frequency ratio (PWM at 2× PFC), and enables IEC 1000-3-2 compliant AC-DC power supplies up to 300 W in boost PFC + flyback configurations.

For engineers reviewing the UCC28517N datasheet, UCC28517N pinout, UCC28517N application, or UCC28517N equivalent, key selection criteria include its programmable PWM maximum duty cycle (70–80%), UVLO2 turn-off threshold of 3.55 V, zero-power detect functionality, and dual-gate-driver timing coordination for reduced boost capacitor ripple.

Technical Context

The UCC28517N implements leading-edge modulation for the PFC stage and trailing-edge modulation for the PWM stage-minimizing ripple current in the boost output capacitor through synchronized phase relationship. Its PFC section uses a highly linear three-input analog multiplier with input voltage feedforward and a transconductance voltage amplifier (g_M = 70–130 µS) for fast load transient response.

The PWM stage features peak-current-mode control with slope compensation via CT_BUFF, programmable soft-start (SS2 charge current −10.5 µA), and independent UVLO2 (6.3–7.3 V turn-on, 3.55 V turn-off). Oscillator frequency is set by RT resistor; for UCC28517N, PWM runs at twice the PFC frequency (e.g., 200 kHz PWM / 100 kHz PFC).

Key Specifications

Pinout & Package

UCC28517N is housed in a 20-pin plastic dual in-line package (PDIP-N), with separate analog ground (GND) and power ground (PWRGND) pins for noise isolation. Thermal dissipation is rated at 1 W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28517N, UCC28517DW offers identical functionality in surface-mount form but lower thermal capacity, while UCC28070 provides superior PFC performance at the cost of added design complexity and component count-making UCC28517N optimal for cost-sensitive, integrated 200–300 W AC-DC systems.

Availability

UCC28517N is available at Aetrix Electronics and suitable for industrial AC-DC power supplies, medical-grade SMPS, and telecom rectifiers requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for UCC28517N 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 and embedded processing technologies, with decades of expertise in power management ICs.

The UCC28517N belongs to TI's UCC2851x family of combination PFC/PWM controllers, designed specifically for cost-optimized, IEC 61000-3-2-compliant offline power supplies up to 300 W.

FAQ

What is the PFC:PWM frequency ratio for UCC28517N?

The UCC28517N implements a fixed 1:2 PFC:PWM frequency ratio-meaning the PWM stage switches at twice the frequency of the PFC stage (e.g., 200 kHz PWM with 100 kHz PFC). This ratio is hard-coded in silicon and cannot be changed. It is selected to reduce ripple current in the boost output capacitor while maintaining manageable switching losses in both stages. The oscillator frequency is set by the RT resistor connected to Pin 2, and the CT_BUFF pin (Pin 5) outputs the PWM ramp signal.

How does UCC28517N implement zero-power detection?

UCC28517N monitors the VAOUT pin (Pin 1) to detect zero-power conditions. When VAOUT falls below 0.33 V (with 40–140 mV hysteresis), the internal zero-power comparator disables GT1 gate drive, turning off the PFC stage. This occurs when output load drops near zero and VAOUT collapses due to lack of feedback current. No external circuitry is required-the function is fully integrated and calibrated. The UCC28517N achieves <0.3 W no-load input power using this mechanism.

What is the purpose of the D_MAX pin on UCC28517N?

The D_MAX pin (Pin 4) on UCC28517N sets the maximum duty cycle for the PWM stage (GT2), clamping it between 70% and 80% depending on applied voltage (0.09–0.90 V). This prevents transformer saturation in flyback or forward converters during overload or startup. It is typically driven by a precision resistor divider from VREF (Pin 20). Unlike generic duty-cycle limits, D_MAX directly interfaces with the PWM comparator's upper threshold, making it a deterministic, voltage-controlled safety feature-not a soft-start or dynamic adjustment.

Can UCC28517N operate with discontinuous conduction mode (DCM) PFC?

No-UCC28517N is explicitly designed for continuous conduction mode (CCM) PFC operation, as confirmed by its average-current-mode control architecture, multiplier-based reference generation, and lack of DCM-specific compensation or timing features. The datasheet specifies CCM as the target operating mode, and the internal current amplifier, VAOUT slew enhancement, and feedforward structure assume inductor current never falls to zero. Using UCC28517N in DCM risks instability, poor THD, and inaccurate power limiting.

What are the UVLO thresholds for UCC28517N?

UCC28517N has two independent undervoltage lockout circuits: VCC UVLO turns on at 10.2 V (±0.5 V) and off at 9.7 V (±0.6 V); PWM-stage UVLO2 turns on at 6.75 V (±0.45 V) and off at 3.55 V (±0.25 V). The 3.2 V hysteresis on UVLO2 enables extended hold-up time-allowing the PWM stage to remain active until the PFC output decays to 47% of nominal. These thresholds are factory-trimmed and not user-adjustable.