STMicroelectronics L4978D

Overview

L4978D from STMicroelectronics is a monolithic step-down switching regulator IC with an integrated 0.25Ω D-MOS power transistor, delivering up to 2A output current across an adjustable output voltage range of 3.3V–50V. It operates from 8V–55V input, features ±1% 3.3V internal reference, adjustable 90–300kHz switching frequency, and supports zero-load operation in inhibit mode for ultra-low quiescent current (100–300µA).

For engineers reviewing the L4978D datasheet, L4978D pinout, L4978D application, or L4978D equivalent, key selection considerations include its voltage feedforward architecture, pulse-by-pulse current limiting, thermal shutdown, soft-start timing control via external capacitor, and SO16W surface-mount package compatibility with high-efficiency DC-DC designs requiring wide VIN and programmable VOUT.

Technical Context

The L4978D implements a voltage-mode PWM controller with internal error amplifier, oscillator with line feedforward (via OSC pin), and bootstrap gate drive for the integrated high-side N-channel DMOS. Its feedback loop accepts direct connection to FB for fixed 3.3V output or uses an external resistive divider for higher regulated outputs.

Protection functions are hardware-based and fully integrated: hiccup-mode short-circuit response, thermal shutdown at ~150°C, feedback disconnection detection, and inhibit-driven sleep mode reducing I_Q to ≤300µA. The device's BCD process enables high efficiency (>90% at 3.3V/2A, V_IN=12V) and fast transient response without external compensation in many configurations.

Key Specifications

Pinout & Package

Package: SO16W (wide-body SOIC-16), surface-mount, 1.27mm pitch, 10.1–10.5mm × 7.4–7.6mm body size, with exposed thermal pad (not electrically connected). Pins 1, 7, 8, 9, 10, 15, 16 are NC (no internal connection).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Compared with LM2678-ADJ and TPS54202, the L4978D uniquely combines wide-input operation (8–55V), integrated 0.25Ω DMOS, voltage feedforward, and true zero-load inhibit-making it optimal for ruggedized, component-minimized buck converters where thermal resilience and input transient tolerance are critical.

Availability

L4978D is available at Aetrix Electronics and suitable for industrial power supplies, automotive body control modules, telecom remote radio units, and test & measurement equipment requiring stable component supply and long-term lifecycle support.

Supply support for L4978D 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, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The L4978D belongs to ST's legacy high-voltage DC-DC regulator product line, engineered for robustness in harsh environments-emphasizing wide input range, integrated power switches, and comprehensive protection for industrial and transportation applications.

FAQ

What is the maximum recommended output current for continuous operation?

The L4978D delivers 2A continuously under typical thermal conditions (T_A ≤ 60°C, SO16W on 2-layer PCB with thermal pad). Derating is required above 60°C ambient or with insufficient copper area-the internal current limit triggers at 2.5–3.5A, but sustained 2A output depends on heatsinking and airflow per the 110°C/W junction-to-ambient thermal resistance spec.

Can the L4978D be used with an input voltage below 8V?

No-operation below 8V violates the absolute maximum rating and causes malfunction. The internal bias circuitry and gate drive require ≥8V to maintain regulation, soft-start, and current limiting functionality. Startup may fail, and output voltage will drop out of regulation if V_IN falls below this threshold during operation.

How does the voltage feedforward function improve performance?

Voltage feedforward is implemented inherently through the OSC pin's dependence on V_IN, causing switching frequency to scale with input voltage. This compensates for duty-cycle variation, reducing output voltage deviation during line transients to <10mV-eliminating need for complex loop compensation in many applications and improving PSRR at low frequencies.

Is the SO16W package RoHS-compliant and lead-free?

Yes-the L4978D SO16W package is RoHS-compliant and lead-free per STMicroelectronics' 2005 product release documentation. It meets JEDEC J-STD-020 moisture sensitivity level MSL3 and supports standard Pb-free reflow profiles with peak temperature ≤260°C.