Texas Instruments UCC38500DWTR

Overview

UCC38500DWTR from Texas Instruments is a dual-stage power factor correction (PFC) and DC-DC controller IC integrating average-current-mode PFC control with peak-current-mode downstream PWM control. It delivers near-unity power factor, programmable 100 kHz oscillator, leading-edge PFC + trailing-edge synchronized second-stage modulation, and 7.5 V reference. Used in universal-input AC-DC supplies like 100-W offline converters with 385 V boost output.

For engineers reviewing the UCC38500DWTR datasheet, UCC38500DWTR pinout, UCC38500DWTR application, or UCC38500DWTR equivalent, key selection criteria include its 16.5 V/10 V UVLO threshold for bootstrap bias operation, dual-gate drivers (GT1/GT2) with 50% max duty cycle clamp on GT2, and integrated feedforward line regulation via VFF pin.

Technical Context

The UCC38500DWTR implements a two-stage control architecture: the PFC stage uses average current-mode control with a high-linearity multiplier (K = 0.5–1.5 V⁻¹), IAC input, and VFF feedforward to maintain constant input power across 85–265 V_RMS input. Its CAOUT current amplifier drives the PFC PWM latch with low offset (±6 mV) and 90 dB open-loop gain.

The second stage employs external error feedback via VERR, peak-current sensing on ISENSE2, and soft-start via SS2 charge current (−7.3 to −12.5 µA). It features programmable UVLO2 thresholds (6.3–7.3 V turn-on, 0.96–1.44 V hysteresis) and internal 4.5 V clamp on VERR to enforce ≤50% duty cycle for transformer reset.

Key Specifications

Pinout & Package

UCC38500DWTR is housed in a 20-pin SOIC (DW) package with exposed thermal pad, optimized for surface-mount assembly and reeled delivery (2000 units/reel).

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28500DW and UCC38502DW, the UCC38500DWTR offers the narrowest temperature rating but lowest cost for commercial-grade 0°C–70°C applications, with tighter UVLO2 hysteresis ensuring earlier shutdown during marginal PFC output conditions-critical for protecting downstream converters.

Availability

UCC38500DWTR is available at Aetrix Electronics and suitable for server power supplies, industrial AC-DC adapters, and medical equipment PSUs requiring stable component supply and long-term production continuity.

Supply support for UCC38500DWTR 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 IC design.

The UCC38500DWTR belongs to TI's UCC2850x/UCC3850x family of integrated PFC + DC-DC controllers, engineered specifically for high-efficiency, low-EMI AC-DC front-end architectures in commercial and industrial power supplies.

FAQ

What is the UVLO threshold configuration of the UCC38500DWTR?

The UCC38500DWTR features a wide UVLO threshold of 16.5 V turn-on and 10 V turn-off for the main VCC supply, enabling reliable bootstrap bias operation across universal AC inputs. Its second-stage UVLO2 has a 6.75 V turn-on threshold with 1.2 V hysteresis, ensuring coordinated start-up only after the PFC output reaches 90% of regulation. This configuration is fixed and not user-programmable on the UCC38500DWTR.

How does the UCC38500DWTR implement feedforward line regulation?

The UCC38500DWTR generates VFF by mirroring half the IAC current into an external RC filter, producing a voltage proportional to RMS line voltage. This VFF signal scales the analog multiplier's gain to maintain constant input power across 85–265 V_RMS, eliminating high-voltage resistive dividers. The UCC38500DWTR's VFF pin directly supports this simplified feedforward architecture without additional components.

Can the UCC38500DWTR support both voltage-mode and current-mode control for the second stage?

Yes, the UCC38500DWTR supports both configurations. For current-mode control, the external error signal is fed into VERR via optocoupler, while ISENSE2 senses peak switch current. For voltage-mode, the CT oscillator ramp can be injected into ISENSE2 through a voltage divider. The UCC38500DWTR's flexible ISENSE2 input and VERR clamp make it adaptable to either topology without hardware change.

What is the purpose of the SS2 pin on the UCC38500DWTR?

The SS2 pin on the UCC38500DWTR controls soft-start for the second-stage DC-DC converter. It sinks a constant −7.3 to −12.5 µA current to charge an external capacitor, generating a slowly rising voltage that acts as the error signal during start-up. This ensures controlled duty-cycle ramp-up, preventing inrush current. During fault or disable, SS2 discharges rapidly to shut down GT2-functionality fully integrated within the UCC38500DWTR.

Does the UCC38500DWTR require an external voltage reference?

No, the UCC38500DWTR integrates a precision 7.5 V reference (VREF) with ±12 mV accuracy over 0°C to 70°C, capable of sourcing up to 10 mA. This reference powers external circuitry and serves as the level-shift source for PKLMT current-limiting resistors. No external reference is needed-the UCC38500DWTR's internal VREF is fully functional and bypassed to GND with a 0.1-µF ceramic capacitor per datasheet guidance.