STMicroelectronics STCMB1TR

Overview

STCMB1TR from STMicroelectronics is a transition-mode PFC + LLC resonant half-bridge combo controller in SO20W package, integrating 800 V HV start-up, active X-cap discharge, and independent debug modes for both converters. It delivers enhanced constant-on-time PFC with THD optimizer, proprietary timeshift control for LLC, and dual-level OCP with hard-switching prevention - enabling ultra-low standby power and compliance with IEC 62368-1 and EuP Lot 6.

For engineers reviewing the STCMB1TR datasheet, STCMB1TR pinout, STCMB1TR application, or STCMB1TR equivalent, this IC supports high-efficiency ac-dc adapters, LED TV/PC SMPS, and street lighting systems requiring coordinated PFC+LLC control, synchronous burst mode, and safety-certified X-cap discharge without external resistors.

Technical Context

The STCMB1TR integrates three functional blocks: a TM PFC controller using input voltage feedforward and cycle-by-cycle OCP; an LLC half-bridge controller employing timeshift modulation (TSC) and self-adjusting deadtime up to 750 kHz; and an 800 V HV start-up generator with integrated X-cap discharge logic triggered by AC line detachment detection.

Its glue logic coordinates power sequencing (PFC-first startup), fault handling (latched FB failure, dual-level HB OCP), and synchronized burst mode where both PFC and LLC operate intermittently at light load - reducing average switching frequency and minimizing no-load consumption while maintaining regulation via optocoupler-coupled RFMIN feedback.

Key Specifications

Pinout & Package

STCMB1TR is housed in a surface-mount SO20W (wide-body SOIC-20) package with internal high-voltage isolation barriers. Pins 2 and 17 are unconnected spacers to ensure ≥8 mm creepage distance between HV and low-voltage sections per safety standards.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28070A and ICE2PCS01, STCMB1TR uniquely integrates PFC+LLC control, HV start-up, X-cap discharge, and synchronized burst mode in one SO20W package - reducing component count by ≥7 parts, simplifying safety certification, and enabling sub-30 mW standby without external circuitry.

Availability

STCMB1TR is available at Aetrix Electronics and suitable for LED TV power supplies, desktop PC SMPS, and LED street lighting drivers requiring stable component supply, long-term lifecycle support, and safety-compliant X-cap discharge functionality.

Supply support for STCMB1TR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, power ICs, and analog/mixed-signal devices for industrial, automotive, and consumer markets.

The STCMB1TR belongs to ST's AC-DC digital power controller product line, engineered specifically for high-efficiency, safety-certified resonant SMPS targeting EuP Lot 6, CoC v5 Tier 2, and IEC 62368-1 compliance.

FAQ

What is the purpose of the HV pin (Pin 1) beyond start-up?

The HV pin serves three critical roles: (1) 800 V-rated input for high-voltage start-up charging of VCC, (2) AC line voltage sensing for brown-in/out protection and input feedforward in PFC control, and (3) trigger for active X-cap discharge upon AC line removal detection. Its internal logic monitors HV pin voltage decay to initiate discharge before the X-cap voltage drops below 60 V, satisfying IEC 62368-1 discharge time requirements.

How does the timeshift control (TSC) improve LLC performance compared to standard frequency modulation?

Timeshift control modulates the phase relationship between half-bridge drive signals instead of shifting switching frequency, enabling faster dynamic response to load transients and superior input ripple rejection. Unlike frequency modulation, TSC maintains near-constant tank frequency, avoiding variable gain in the resonant network and preserving ZVS across wide line/load ranges - resulting in tighter output regulation and reduced output capacitor stress.

Can STCMB1TR operate without an optocoupler in the feedback loop?

No - STCMB1TR requires an optocoupler for primary-side regulation. The RFMIN pin accepts phototransistor collector current to close the LLC output voltage feedback loop via timeshift modulation. Removing the optocoupler disables regulation, causing uncontrolled output voltage rise and triggering OVP protection. Secondary-side shunt regulators (e.g., TL431) must be used with optocouplers; direct primary sensing is not supported.

What happens during simultaneous PFC and LLC fault conditions?

When both PFC and LLC detect latched faults (e.g., FB < 0.5 V + ISEN_HB > 1.5 V), STCMB1TR enters full-system latch-off: HV start-up generator cycles at reduced current to maintain minimal VCC bias, GD_PFC/LVG/HVG outputs are forced low, and restart requires full AC cycle removal. This prevents cascading failures and ensures safe thermal shutdown while retaining fault visibility via FB and ISEN_HB pin states.