STMicroelectronics L4984DTR

Overview

L4984DTR from STMicroelectronics is a current-mode CCM Power Factor Correction (PFC) controller using line-modulated fixed-off-time (LM-FOT) control, designed for boost-type pre-regulators in 1 kW+ switch-mode power supplies. It features a proprietary multiplier for THD minimization, bi-directional 1/V² voltage feedforward, 1% internal reference (at Tj = 25 °C), and a ±600/±800 mA totem-pole gate driver in SSOP10 package-enabling IEC61000-3-2-compliant desktop PC and server power supplies.

For engineers reviewing the L4984DTR datasheet, L4984DTR pinout, L4984DTR application, or L4984DTR equivalent, key selection criteria include LM-FOT modulation stability, THD optimizer circuit performance, OVP/FFD latch behavior, and compatibility with high-current MOSFETs or IGBTs in continuous conduction mode PFC stages.

Technical Context

The L4984DTR implements a proprietary line-modulated fixed-off-time modulator that maintains near-fixed switching frequency across AC line half-cycles while operating in CCM, unlike traditional critical-conduction-mode controllers. Its multiplier accepts MULT (pin 3) and VFF (pin 5) inputs to generate a sinusoidal current reference, with built-in 1/V² correction enabling robust line transient response during mains surges and brownouts.

Internal protection includes latched shutdown on feedback loop failure (detected via INV < 1.66 V concurrent with PFC_OK > 2.5 V), inductor saturation detection at 1.7 V on CS (pin 4), and digital leading-edge blanking (145–400 ns). The gate driver delivers 600 mA source / 800 mA sink with active pull-down during UVLO and 12 V output clamping.

Key Specifications

Pinout & Package

SSOP10 package: 10-pin shrink small-outline package with 0.65 mm pitch, 4.4 mm × 3.0 mm body, and exposed thermal pad (per ST DocID024474 Rev 1, Figure 38).

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28070DR and FAN4803SMX, the L4984DTR uniquely integrates LM-FOT modulation, THD optimization, and latched FFD in a single SSOP10 package-reducing BOM count and improving reliability in 1 kW+ IEC61000-3-2-compliant systems without requiring phase management or external protection ICs.

Availability

L4984DTR is available at Aetrix Electronics and suitable for desktop PC power supplies, server SMPS, industrial motor drives, and medical imaging power systems requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for L4984DTR 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 analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The L4984DTR belongs to ST's high-efficiency AC-DC power conversion product line, engineered specifically for cost-sensitive, high-power-factor, CCM-based PFC pre-regulators in computing and industrial power supplies.

FAQ

What is the purpose of the TIMER pin (pin 7) in the L4984DTR?

The TIMER pin programs the off-time of the external MOSFET via an external capacitor (CTIMER). An internal 142–163 µA current charges CTIMER during MOSFET off-time; when its voltage matches the MULT pin voltage, the off-time ends and the gate driver turns on. This LM-FOT mechanism ensures stable CCM operation with near-constant frequency across the AC line cycle.

How does the L4984DTR implement brownout protection?

Brownout protection is implemented on the VFF pin (pin 5): when voltage drops below 0.8 V, the IC shuts down non-latched and enters low-consumption state; restart occurs automatically when VFF rises above 0.88 V. This function uses the same internal comparator that supports 1/V² feedforward, ensuring coordinated response to line undervoltage without external components.

Can the L4984DTR be used in discontinuous conduction mode (DCM)?

No-the L4984DTR is explicitly designed for continuous conduction mode (CCM) PFC operation only. Its LM-FOT modulator, multiplier architecture, and protection thresholds (e.g., 1.7 V CS saturation detection) assume CCM waveforms. Attempting DCM operation results in unstable current shaping, excessive THD, and potential false saturation triggers due to inherent current zero-crossing behavior.

What happens during feedback loop failure (FFD) and how is it cleared?

FFD occurs when INV voltage falls below 1.66 V *while* PFC_OK voltage exceeds 2.5 V-indicating open-loop regulator failure. The device enters latched shutdown: GD stops switching, COMP is clamped low, and VCC must be cycled to reset. This prevents uncontrolled output voltage rise and capacitor overvoltage, meeting safety requirements for Class II isolated supplies.