STMicroelectronics L4973V5.1

Overview

L4973V5.1 from STMicroelectronics is a monolithic step-down switching regulator delivering 3.5 A at a fixed 5.1 V ±1% output, operating from 8 V to 55 V input, featuring internal 0.15 Ω D-MOS transistor, voltage feed-forward regulation, and soft-start-used in industrial power supplies for DIN-rail-mounted PLC I/O modules requiring high-efficiency, wide-input DC-DC conversion.

For engineers reviewing the L4973V5.1 datasheet, L4973V5.1 pinout, L4973V5.1 application, or L4973V5.1 equivalent, key selection criteria include its 5.1 V reference accuracy (±1.5%), hiccup-mode short-circuit protection, synchronization capability, and SO-20 (12+4+4) thermal performance under 55 V input transients.

Technical Context

The L4973V5.1 integrates a BCD-process D-MOS power switch with 0.15 Ω typical R_DS(on), enabling high efficiency up to 90% at 3.5 A/5.1 V. Its voltage feed-forward architecture dynamically adjusts switching duty cycle in response to input voltage changes, improving line regulation to ±5 mV across 8–55 V.

Internal error amplifier provides 60 dB open-loop gain and 2.5 mS transconductance; oscillator supports adjustable frequency up to 300 kHz via external R/C network, with ±5% stability over supply voltage and temperature. Soft-start uses programmable capacitor-based ramp (30–60 µA charge current) to limit inrush.

Key Specifications

Pinout & Package

Package: SO-20 (12+4+4), surface-mount, ECOPACK-compliant, with 12 power/signal pins (including dual OUT, dual VCC, quad GND), 4 bootstrap/sync pins (BOOT, SYNC, INH, OSC), and 4 control/reference pins (VFB, COMP, V5.1, SS).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2596S-5.0 and MP2451DT-LF-Z, the L4973V5.1 uniquely combines 3.5 A capability, 55 V input tolerance, hiccup-mode safety, and an accessible 5.1 V reference-making it the only single-chip solution for ruggedized 5 V industrial power rails requiring field reliability and thermal margin.

Availability

L4973V5.1 is available at Aetrix Electronics and suitable for industrial automation power supplies, automotive body control modules, and telecom remote radio units requiring stable component supply with long-term lifecycle assurance.

Supply support for L4973V5.1 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, microcontrollers, and automotive ICs-with over 30 years of industrial-grade analog product heritage.

The L4973 series belongs to ST's high-voltage monolithic buck regulator family, designed specifically for rugged 24 V/48 V industrial and transportation systems demanding wide-input operation, fault resilience, and minimal external components.

FAQ

What is the minimum input voltage required for regulation at 5.1 V output?

The L4973V5.1 requires a minimum input voltage of 8 V to maintain regulation at 5.1 V output, due to internal dropout constraints and bootstrap capacitor charging requirements. Below 8 V, the device enters undervoltage lockout and ceases switching-verified per Table 4's "Input voltage range" specification (8–55 V) and Figure 20's dropout voltage curve showing ~0.4 V headroom at 3.5 A.

Can the L4973V5.1 be used with an adjustable output voltage higher than 5.1 V?

Yes-the L4973V5.1 supports adjustable outputs from 5.1 V to 50 V using an external resistive divider on the VFB pin, as confirmed in the "Features" section and Figure 4's application circuit. The internal 5.1 V reference remains active, but feedback scaling allows precise higher-voltage regulation without modifying internal circuitry.

How does the SYNC pin function in master vs. slave configuration?

The SYNC pin operates bidirectionally: when driven with a 3–5 V square wave (≥100 kHz), it forces the L4973V5.1 to synchronize as a slave; when left open or pulled high, it sources a 4–4.5 V output pulse (0.2–0.35 µs width) to synchronize external converters as a master-per Table 4's "Sync function" parameters and Figure 40's synchronization example.

Is thermal derating required when operating above 25 °C ambient?

Yes-thermal derating is mandatory. With R_thJA = 80 °C/W and maximum junction temperature of 150 °C, the allowable power dissipation drops from 4 W at 25 °C ambient to ~2.4 W at 70 °C ambient. This corresponds to ~2.2 A at 5.1 V output under worst-case 55 V input-per Table 2's "Power dissipation" and Figure 29's P_diss vs. V_IN curves.