STMicroelectronics STCMB1

Overview

STCMB1 from STMicroelectronics is a dual-function 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. It delivers enhanced constant on-time PFC with THD optimizer, proprietary timeshift control for LLC, and full protection suites including ac brown-in/out, two-level OCP, HSP, and latched feedback failure detection - deployed in energy-compliant LED TV and open-frame SMPS.

For engineers reviewing the STCMB1 datasheet, STCMB1 pinout, STCMB1 application, or STCMB1 equivalent, key selection considerations include its integrated HV start-up with input voltage sensing, synchronous burst mode coordination between PFC and LLC, self-adjusting deadtime up to 750 kHz, and IEC 62368-1–compliant X-cap discharge without external resistors.

Technical Context

The STCMB1 integrates three core subsystems: a TM PFC controller using enhanced constant-on-time (COT) with input voltage feedforward and THD optimization; an LLC half-bridge controller employing proprietary timeshift control (TSC) for improved ripple rejection and dynamic response; and an 800 V-rated high-voltage start-up generator with active X-cap discharge logic triggered by AC line detachment detection.

Its glue logic coordinates power sequencing (PFC starts first, HB enables at FB > 2.4 V), fault handling (latched FB < 0.5 V disables both stages), and synchronized light-load operation - where burst mode forces intermittent, phase-aligned switching of both PFC and LLC to minimize standby consumption while maintaining regulation.

Key Specifications

Pinout & Package

STCMB1 is housed in a SO20W (wide-body SOIC-20) package with internal high-voltage isolation spacers at pins 2 and 17. The layout separates HV (pin 1), signal (pins 3–11), gate drive (pins 14, 16, 19), and floating supply (pins 18, 20) domains to meet IEC 62368-1 creepage and clearance requirements.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28070 and ICE2PCS01, STCMB1 uniquely integrates HV start-up, X-cap discharge, and timeshift-controlled LLC in one SO20W package - enabling compact, ultra-low-standby, safety-certified designs below 250 W without external coordination logic.

Availability

STCMB1 is available at Aetrix Electronics and suitable for LED TV power supplies, open-frame SMPS, desktop PC PSUs, and LED street lighting drivers requiring stable component supply, long-term lifecycle support, and compliance with EuP Lot 6, DOE Level VI, and CoC v5 Tier 2.

Supply support for STCMB1 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 STCMB1 belongs to ST's AC-DC digital power controller product line, engineered specifically for high-efficiency, low-standby, safety-certified combo PFC+LLC solutions targeting next-generation energy regulations and compact form factors.

FAQ

What is the maximum recommended operating frequency for the LLC section?

The STCMB1 supports LLC half-bridge operation up to 750 kHz with self-adjusting deadtime. This maximum is validated across temperature (−40°C to +125°C) and input voltage (85–265 VAC), ensuring zero-voltage switching (ZVS) is maintained even at full load and elevated junction temperatures. Operation beyond 750 kHz risks loss of ZVS and increased switching losses.

How does the X-cap discharge function activate and what voltage threshold triggers it?

The X-cap discharge activates automatically when the HV pin detects AC line removal - confirmed by sustained absence of AC voltage waveform and decay of internal HV generator activity. It discharges X-capacitors to <60 V within ≤2 seconds, complying with IEC 62368-1 Annex G. No external trigger or control signal is required; activation is fully autonomous and internally timed.

Can STCMB1 operate with a non-isolated PFC stage?

No. STCMB1 requires isolated feedback for the PFC stage via optocoupler-connected RFMIN pin to close the output voltage regulation loop using timeshift modulation. Its PFC control architecture relies on sensed output voltage (FB pin) and opto-coupled error signal (RFMIN) - non-isolated configurations lack the necessary feedback path and violate functional safety design assumptions.

What is the minimum recommended value for the RC filter on the STBY pin?

The STBY pin requires an RC filter with R > 100 Ω and C > 100 pF, as specified in the datasheet. A typical design uses 10 kΩ and 1 nF (τ = 10 µs), which provides adequate noise immunity while preserving loop stability. Values below these minima risk false burst-mode triggering due to noise coupling or instability in the feedback path.