STMicroelectronics L4984D

Overview

L4984D from STMicroelectronics is a current-mode CCM Power Factor Correction (PFC) controller using line-modulated fixed-off-time (LM-FOT) control architecture. It delivers near-fixed-frequency operation in boost PFC pre-regulators, features 1% internal reference voltage (at Tj = 25 °C), 600 mA source / 800 mA sink totem-pole gate driver, and integrated 1/V² voltage feedforward for low THD (<5% typical over 20–100% load). It targets IEC61000-3-2-compliant SMPS above 1 kW, including server and high-end desktop power supplies.

For engineers reviewing the L4984D datasheet, L4984D pinout, L4984D application, or L4984D equivalent, this controller offers verified CCM PFC design support with brownout detection, latched feedback failure shutdown, inductor saturation protection, and digital leading-edge blanking - all in SSOP10 package with validated thermal performance up to 150 °C junction temperature.

Technical Context

The L4984D implements a proprietary LM-FOT modulator that generates variable off-time based on rectified mains voltage (via MULT pin) and a precise internal timer ramp (charged by 153 µA current at MULT = 1 V), enabling stable CCM operation across universal AC input (85–265 VAC). Its multiplier includes 1/V² correction via VFF pin with RFF/CFF network, delivering bi-directional line transient response during surges and sags.

It integrates dual-protection logic: OVP triggers at 2.5 V on PFC_OK pin (with 2.4 V restart threshold), while feedback loop failure is detected when INV falls below 1.66 V simultaneously with PFC_OK ≥ 2.5 V - resulting in latched shutdown requiring VCC cycle. The CS pin incorporates 1.7 V saturation threshold and 220 ns digital blanking for noise-immune current sensing.

Key Specifications

Pinout & Package

SSOP10 package: 3.9 mm × 4.9 mm body, 0.65 mm pitch, exposed pad optional; suitable for high-density server PSU layouts with thermal relief via GND pad connection.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28070 and FAN9612, the L4984D uniquely combines LM-FOT control, integrated 1/V² feedforward, latched FFD, and robust 600/800 mA gate drive - making it optimal for 1–2 kW server and medical PSUs demanding reliability, low THD, and autonomous protection.

Availability

L4984D is available at Aetrix Electronics and suitable for server power supplies, medical imaging systems, and industrial motor drives requiring stable component supply with full production lifecycle support.

Supply support for L4984D 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, specializing in power management, analog, and microcontroller solutions for industrial, automotive, and computing markets.

The L4984D belongs to ST's high-voltage analog PFC controller product line, designed specifically for CCM boost topologies in energy-efficient, standards-compliant AC-DC conversion systems above 1 kW.

FAQ

What is the purpose of the VFF pin on the L4984D?

The VFF pin implements the 1/V² voltage feedforward function by accepting a DC voltage proportional to the peak AC line voltage (via RFF/CFF network). It linearizes the current loop gain across input voltage variations, reducing THD and improving line transient response. It also serves as the brownout detector input, shutting down the IC when voltage drops below 0.8 V and restarting at 0.88 V.

How does the L4984D protect against feedback loop failure?

The L4984D detects feedback loop failure (FFD) when the INV pin voltage falls below 1.66 V while the PFC_OK pin voltage remains at or above 2.5 V - indicating an open feedback divider or failed optocoupler. This triggers a latched shutdown; recovery requires cycling VCC. Unlike simple OVP, FFD prevents uncontrolled output voltage rise under fault conditions.

Can the L4984D be used in discontinuous conduction mode (DCM)?

No - the L4984D is explicitly designed for continuous conduction mode (CCM) boost PFC operation. Its LM-FOT control architecture, multiplier design, and protection features (e.g., inductor saturation detection) assume CCM waveforms. Using it in DCM results in unstable regulation, excessive THD, and potential failure of the 1.7 V CS threshold protection mechanism.

What is the recommended timing capacitor value for 70 kHz operation?

For nominal 70 kHz switching frequency, a 470 pF capacitor between TIMER pin (7) and GND is specified in the datasheet. This yields a typical off-time of 3.09 µs at VMULT = 1 V, which - combined with variable on-time determined by current zero-crossing - achieves the target frequency across line and load. Deviations beyond 0.1–2.2 nF range cause timing inaccuracy or instability.